3.2 Ranking Acids and Bases | Organic Chemistry

00:35:47
https://www.youtube.com/watch?v=ucC9IhQX6JU

الملخص

TLDRIn this lesson, the concept of ranking acids and bases based on their structural features is explored. The discussion focuses on how to compare the relative acidities and basicities of acids and bases by applying specific rules. A key highlight is the mnemonic 'REO' used for ranking. This stands for Atom, Resonance, Induction, and Orbitals, though the rule concerning charge is also discussed as a subsidiary component. The video clarifies that a stronger acid has a weaker conjugate base and vice versa and illustrates examples where the stability of bases, the size of atoms, or resonance can impact their corresponding acid or base strengths. Key points include: 1. A more stable base is often a weaker base due to lower energy electrons, and charge can affect energy levels significantly. 2. The sequence of considering Atom, Resonance, Induction, and Orbitals helps rank the bases effectively. 3. The mnemonic is primarily for bases having similar charges. 4. Memorizing pKa values can resolve instances where structural analysis is not straightforward. 5. Inductive effects can stabilize a base, as demonstrated by electronegative atoms withdrawing electron density. 6. Changes in hybridization states (e.g., sp, sp2, sp3) impact the stability and thus basicity of atoms in compounds. The lesson emphasizes understanding these principles can aid in predicting relative reactivity in chemical reactions, imperative for organic chemistry.

الوجبات الجاهزة

  • 🔍 Understanding rules is key: Understanding and applying the mnemonic 'REO' helps in ranking bases and analyzing acidity.
  • 🔓 Charge matters: More negative charge correlates with a stronger base, while more positive with stronger acid.
  • 🔬 Size affects basicity: Smaller atoms form stronger bases.
  • 🌐 Resonance stabilizes bases: Resonance decreases electron energy, leading to weaker bases.
  • ⚛️ Atom matters: The atom's position in the periodic table influences base strength.
  • 🔧 Induction helps stabilize: Electronegative atoms nearby reduce a base's negativity, stabilizing it.
  • 🔄 Hybridization affects basicity: sp hybridized atoms have more stable, lower energy electrons than sp2 or sp3.
  • 📏 Memorized pKa values are crucial: They help when structural clues are ambiguous.
  • 📉 Strong acids have weak bases: Inversely, weak acids have strong conjugate bases.
  • 📖 Examples solidify understanding: Practical examples illustrate each rule's application.

الجدول الزمني

  • 00:00:00 - 00:05:00

    The lesson focuses on ranking acids and bases, highlighting various structural features that affect acidity and basicity. It emphasizes the inverse relationship between acid strength and the stability of its conjugate base and introduces the concept of electron energy relevance to base stability.

  • 00:05:00 - 00:10:00

    The mnemonic 'REO' is introduced for comparing bases, especially when they have the same charge. The rank of bases considers factors like atom type, resonance, induction, and hybridization, emphasizing charge importance in these comparisons.

  • 00:10:00 - 00:15:00

    Charge impacts the energy of electrons, influencing base strength. Bases with negative charges have higher energy electrons, making them more reactive, whereas positive charges result in lower energy, less reactive bases. Charge is crucial but specific to conjugate acid-base comparisons.

  • 00:15:00 - 00:20:00

    The atom rule's significance is discussed, focusing on size and electronegativity on the periodic table to determine base strength. It's explained that base strength can be influenced by the element's position on the periodic table regarding size and electronegativity.

  • 00:20:00 - 00:25:00

    Resonance stabilizes bases and is critical in ranking them. More resonance structures generally mean a weaker base. The lesson also cautions against relying solely on the number of resonance structures without considering the quality of those structures relative to different atoms.

  • 00:25:00 - 00:30:00

    Inductive effects of electronegative atoms help stabilize bases. Proximity and type of electronegative atom affect stabilization strength; closer or more electronegative atoms result in a more stabilized, weaker base. Multiple electronegative atoms enhance stabilization further.

  • 00:30:00 - 00:35:47

    The role of orbitals in base strength through hybridization differences is highlighted. Bases with lone pairs in sp hybridized orbitals are more stable compared to sp2 or sp3 hybridization. This rule, though less frequent, is integral to understanding base comparisons in specific scenarios.

اعرض المزيد

الخريطة الذهنية

Mind Map

الأسئلة الشائعة

  • What mnemonic is used to rank bases?

    The mnemonic 'REO' is used to rank bases: Atom, Resonance, Induction, and Orbitals.

  • How does the charge affect acidity and basicity?

    The charge affects acidity and basicity as a more negative charge generally means a stronger base, while a more positive charge is linked to a stronger acid.

  • What is the relationship between acids and their conjugate bases?

    The stronger an acid, the weaker its conjugate base and vice versa.

  • Why is resonance important in determining acid and base strength?

    Resonance stabilizes a base, making it weaker because it lowers the energy of the electrons.

  • How does atom size affect basicity?

    Smaller atoms make stronger bases due to shorter, stronger bonds to H+.

  • What does induction mean in the context of acids and bases?

    Induction refers to the effect of nearby electronegative atoms pulling electron density away, stabilizing a base.

  • How does hybridization affect base strength?

    Lone pairs on sp hybridized atoms are more stable (weaker base) than on sp3 hybridized ones.

  • Can electronegativity influence acid strength?

    Yes, less electronegative atoms have weaker bases, hence stronger conjugate acids.

  • What role do memorized pKa values play?

    Memorized pKa values help confirm acid rankings when structural rule assessments might lead to confusion.

  • What is the significance of atomic positioning in relation to electronegative atoms?

    The closer an electronegative atom is to the base, the more it stabilizes due to induction.

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التمرير التلقائي:
  • 00:00:01
    ranking acids and bases that'll be the
  • 00:00:02
    topic in this lesson now
  • 00:00:04
    we just had an introduction to acids and
  • 00:00:05
    bases in the last lesson and now we're
  • 00:00:07
    really going to learn
  • 00:00:08
    uh all the different structural features
  • 00:00:10
    that allow us to actually compare the
  • 00:00:11
    relative acidities between two acids
  • 00:00:13
    or the relative basicities between a
  • 00:00:15
    couple of bases as well
  • 00:00:16
    now this is my brand new organic
  • 00:00:18
    chemistry playlist i'll be releasing
  • 00:00:20
    these lessons weekly throughout the
  • 00:00:21
    2020-21 school year
  • 00:00:22
    so if you don't want to miss one of
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    these subscribe to the channel click the
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    bell notifications you'll be notified
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    every time i post a new video
  • 00:00:34
    so ranking acid bases i just want to
  • 00:00:36
    start off with a little reminder from
  • 00:00:37
    our introduction in the last lesson that
  • 00:00:38
    the stronger an acid the weaker its
  • 00:00:41
    conjugate base and vice versa so if you
  • 00:00:43
    have a stronger conjugate base you're
  • 00:00:44
    going to have a weaker
  • 00:00:46
    acid associated with that and so next
  • 00:00:47
    part of that is going to be that a more
  • 00:00:49
    stable base is a weaker base so that's
  • 00:00:52
    the next part and then
  • 00:00:53
    more stable base is usually going to
  • 00:00:56
    mean lower energy electrons on the base
  • 00:00:58
    now recall that
  • 00:00:59
    lewis definition of base was an electron
  • 00:01:00
    pair donor and usually lower energy
  • 00:01:03
    electrons mean more
  • 00:01:04
    stable electrons less reactive electrons
  • 00:01:07
    we'll see one major exception to that
  • 00:01:08
    but most of the time
  • 00:01:09
    that's kind of how we're going to rank
  • 00:01:11
    bases we're going to look at how low the
  • 00:01:13
    energy of the electrons are
  • 00:01:14
    and their relative stabilities
  • 00:01:16
    associated with that so lower energy
  • 00:01:17
    electrons
  • 00:01:18
    more stable base more stable base weaker
  • 00:01:21
    base
  • 00:01:21
    all right so we're going to use a little
  • 00:01:24
    mnemonic here and in this case i'm going
  • 00:01:26
    to use
  • 00:01:26
    reo so but the truth is we only use reo
  • 00:01:29
    if we're comparing
  • 00:01:30
    bases first off these are mnemonic for
  • 00:01:32
    comparing bases
  • 00:01:34
    but we only use it if we're comparing a
  • 00:01:35
    bunch of bases that all have the same
  • 00:01:37
    charge now and most of the time we'll be
  • 00:01:40
    using bases that have a negative charge
  • 00:01:41
    but this could apply to comparing bases
  • 00:01:43
    that are all neutral in charge and
  • 00:01:44
    things of a sort as well so
  • 00:01:46
    so i want to want to put charge at the
  • 00:01:47
    top of the list although it's not a
  • 00:01:49
    part of the the proper mnemonic now
  • 00:01:50
    other textbooks
  • 00:01:52
    uh and professors will often use a
  • 00:01:54
    version of this mnemonic that includes
  • 00:01:55
    charge
  • 00:01:56
    and they would call it cardio and
  • 00:01:58
    induction here instead of calling it
  • 00:01:59
    induction they might call it
  • 00:02:00
    dipole induction so they can put the d
  • 00:02:02
    and the i on that because cardio is just
  • 00:02:04
    a really cool one so
  • 00:02:06
    and it starts with charge so charge is
  • 00:02:07
    really important we'll get into that in
  • 00:02:08
    a little bit and
  • 00:02:09
    and then the atom actually acting as the
  • 00:02:11
    base and where it's located on the
  • 00:02:12
    periodic table that'll be important in
  • 00:02:13
    determining relative basicity
  • 00:02:15
    uh and then resonance we you know we've
  • 00:02:17
    learned about resonance stabilization
  • 00:02:18
    and how
  • 00:02:19
    that could stabilize the base and make
  • 00:02:20
    it a weaker base as well and induction
  • 00:02:22
    is one we haven't specifically talked
  • 00:02:24
    about yet
  • 00:02:24
    maybe you saw it in gen chem maybe it
  • 00:02:26
    didn't depends on your class so
  • 00:02:28
    but induction means do you have any
  • 00:02:29
    electronegative atoms nearby
  • 00:02:31
    so that might help stabilize a base it
  • 00:02:33
    turns out having electronegative atoms
  • 00:02:34
    are going to pull electrons towards them
  • 00:02:36
    and lower the electron density on that
  • 00:02:38
    base making it a more stable base less
  • 00:02:40
    negative sort of thing
  • 00:02:41
    uh we'll get more into that a little bit
  • 00:02:42
    and then finally orbitals and this last
  • 00:02:44
    one really
  • 00:02:45
    should you know be called hybridization
  • 00:02:46
    because it's really a difference in
  • 00:02:47
    hybridization of the orbitals of where
  • 00:02:50
    you find a lone pair of electrons but
  • 00:02:51
    that wouldn't make a good
  • 00:02:53
    mnemonic you know are or something like
  • 00:02:55
    that you know so reo they go with
  • 00:02:57
    orbitals but it's really a matter of
  • 00:02:58
    hybridization
  • 00:02:59
    but this little mnemonic is the one
  • 00:03:01
    we're going to use and you typically
  • 00:03:02
    follow it
  • 00:03:03
    in order and most the time again 99 of
  • 00:03:06
    the time
  • 00:03:07
    you're just going to be comparing a
  • 00:03:08
    bunch of bases that all have the same
  • 00:03:10
    charge and so this little charge rule
  • 00:03:12
    becomes irrelevant and that's why it
  • 00:03:14
    really just reduces down to reo but for
  • 00:03:15
    that
  • 00:03:16
    one time out of a hundred i put the
  • 00:03:18
    charge at the top of the list here
  • 00:03:19
    so let's take a look we're gonna take an
  • 00:03:20
    in-depth look at every single one of
  • 00:03:22
    these rules
  • 00:03:23
    so that you can rank acids and bases in
  • 00:03:25
    their relative acidity or relative
  • 00:03:26
    basicity
  • 00:03:27
    just based on looking at their
  • 00:03:28
    structures with no pkas provided
  • 00:03:32
    all right so charge here so it turns out
  • 00:03:34
    when you get a
  • 00:03:35
    negative charge that raises the energy
  • 00:03:37
    of the electrons and you have more
  • 00:03:38
    electrons around that oxygen nucleus
  • 00:03:40
    they can't get as close to the nucleus
  • 00:03:41
    because they're repelling each other and
  • 00:03:42
    so they spread out
  • 00:03:43
    and the further they get out from that
  • 00:03:45
    nucleus the higher their energy and the
  • 00:03:47
    greater the reactivity
  • 00:03:48
    as a base and so having a negative
  • 00:03:51
    charge causes your electron cloud to be
  • 00:03:53
    bigger the electrons are on average
  • 00:03:54
    further from the nucleus
  • 00:03:55
    and it leads to a stronger base now a
  • 00:03:58
    positive charge is going to do the exact
  • 00:04:00
    opposite if i was actually talking about
  • 00:04:01
    this guy is acting like a base here
  • 00:04:03
    that lone pair because now we have a
  • 00:04:05
    positive formal charge in the auction
  • 00:04:06
    with
  • 00:04:07
    fewer electrons around the nucleus which
  • 00:04:08
    means the remaining electrons can
  • 00:04:10
    actually get even closer to the nucleus
  • 00:04:12
    which lowers their energy and makes them
  • 00:04:13
    less reactive and so in this case if we
  • 00:04:15
    were going to look at a trend in
  • 00:04:17
    basicity
  • 00:04:23
    so it would be going to the left and if
  • 00:04:25
    we want to talk about the stability of
  • 00:04:26
    the electrons
  • 00:04:27
    the electrons would actually be getting
  • 00:04:28
    more stable as they went to the right
  • 00:04:31
    so that would relate to basicity here so
  • 00:04:33
    it turns out for charge though you could
  • 00:04:35
    also look at this in terms of
  • 00:04:36
    acidity in this one case and and notice
  • 00:04:38
    we've got hydronium over here hydroxide
  • 00:04:41
    over here we know hydronium
  • 00:04:42
    is a strong acid we know hydroxide's a
  • 00:04:43
    strong base and we got water right in
  • 00:04:45
    the middle which is neutral
  • 00:04:46
    and so you can look at this
  • 00:04:53
    like so cool so charge in this one
  • 00:04:57
    example here this set of examples is
  • 00:04:59
    you got to be careful on when it's
  • 00:05:00
    relevant because it's not going to
  • 00:05:01
    always be relevant now
  • 00:05:03
    as long as you're comparing a conjugate
  • 00:05:04
    base to a conjugate acid conjugate
  • 00:05:06
    conjugate base
  • 00:05:07
    that's when charge will work every time
  • 00:05:09
    as long as you're just comparing a
  • 00:05:10
    conjugate acid a conjugate base
  • 00:05:12
    yes whichever one of these is more
  • 00:05:13
    negative is the better base
  • 00:05:15
    whichever one of these is more positive
  • 00:05:17
    or less negative is the better acid
  • 00:05:19
    that's when it works now if you try to
  • 00:05:21
    compare just two totally different
  • 00:05:23
    molecules that have a different charge
  • 00:05:25
    maybe it'll work and maybe it won't and
  • 00:05:27
    it's not a comparison that comes up a
  • 00:05:28
    lot as a result because it's hard to ask
  • 00:05:30
    you about it
  • 00:05:31
    now if it involves one of the acids that
  • 00:05:34
    you're supposed to memorize the pkas for
  • 00:05:35
    one of those typical functional groups
  • 00:05:36
    that we went through
  • 00:05:37
    in the last lesson well the model means
  • 00:05:39
    that's fair game and you wouldn't even
  • 00:05:40
    need to use rules and you shouldn't use
  • 00:05:42
    rules in that case and i'll show you a
  • 00:05:43
    couple examples where that happens
  • 00:05:45
    so but i just want to point out that
  • 00:05:48
    charge is important and it's probably
  • 00:05:50
    the most important thing however
  • 00:05:53
    most of the time you're not going to be
  • 00:05:54
    comparing acids or bases that have any
  • 00:05:57
    difference in charge and so most of the
  • 00:05:58
    time
  • 00:05:59
    this will just be a moot point but i did
  • 00:06:01
    want to cover my bases and i definitely
  • 00:06:02
    want to relate it to the energies of
  • 00:06:04
    electrons as well and again negative
  • 00:06:06
    charge higher energy electrons positive
  • 00:06:08
    charge
  • 00:06:08
    lower energy electrons okay so now let's
  • 00:06:11
    get into that mnemonic proper so
  • 00:06:13
    once you verify that what you're
  • 00:06:14
    comparing has the same charge you next
  • 00:06:16
    kind of follow these
  • 00:06:17
    this mnemonic in order so the first rule
  • 00:06:19
    you'll consider is adam
  • 00:06:21
    and if you don't find a difference there
  • 00:06:22
    then you'd move on to resonance and if
  • 00:06:23
    you still don't find
  • 00:06:24
    the distinguishing difference there
  • 00:06:25
    you'd move on to induction and if you
  • 00:06:27
    still don't
  • 00:06:28
    find the you know a distinguishing
  • 00:06:29
    difference there you'd move on to
  • 00:06:30
    orbitals
  • 00:06:31
    so these are ranked kind of in like
  • 00:06:33
    order of priority so the atom rule is
  • 00:06:35
    the most important again after charge
  • 00:06:36
    so but then resonance then induction
  • 00:06:38
    then orbitals and again this is not a
  • 00:06:40
    perfect set of rules and there is no
  • 00:06:41
    perfect set of rules so but this will
  • 00:06:43
    work usually you know at least 90
  • 00:06:45
    percent of the time this will lead you
  • 00:06:47
    to the right conclusions as far as
  • 00:06:49
    relative acidity and basicity
  • 00:06:50
    and when these won't lead to the right
  • 00:06:52
    path that's why we memorized some pkas
  • 00:06:54
    earlier because that
  • 00:06:56
    would kind of take care of those
  • 00:06:57
    exceptions so before i ever use these
  • 00:06:59
    rules if i'm ranking acids i look at
  • 00:07:00
    pkas first
  • 00:07:01
    the ones i've memorized so but if i
  • 00:07:03
    don't know the appropriate pkas
  • 00:07:04
    then i go to my rules and rank my
  • 00:07:07
    relative acidity and basically so
  • 00:07:09
    this atom rule the way this works if we
  • 00:07:11
    look at relative basicity on the
  • 00:07:12
    periodic table and
  • 00:07:13
    i know you can't see the whole periodic
  • 00:07:14
    table but it just needed you to be able
  • 00:07:15
    to see the non-metals
  • 00:07:17
    that'll show up in our organic compounds
  • 00:07:19
    and it turns out basicity increases as
  • 00:07:21
    you get
  • 00:07:22
    smaller and as you get less
  • 00:07:25
    electronegative
  • 00:07:26
    so and there's two parts to this so the
  • 00:07:28
    vertical part of that trend
  • 00:07:29
    is all about size and it turns out a
  • 00:07:31
    smaller base makes a shorter bond
  • 00:07:34
    to an h plus ion and a shorter bond is a
  • 00:07:36
    stronger bond and so as a result the
  • 00:07:38
    smaller
  • 00:07:39
    base is the stronger base so and then
  • 00:07:41
    finally as you go from right to left
  • 00:07:43
    within a period now
  • 00:07:44
    if you're comparing elements within a
  • 00:07:45
    period it's not about size anymore
  • 00:07:47
    because they're all really close in size
  • 00:07:49
    and it turns out to be more about
  • 00:07:50
    electronegativity instead
  • 00:07:53
    and it turns out the less
  • 00:07:54
    electronegative base is the less
  • 00:07:56
    stable base and the stronger base so as
  • 00:07:58
    long as you're comparing in the same
  • 00:08:00
    group
  • 00:08:00
    your comparison is about
  • 00:08:01
    electronegativity as long as you're
  • 00:08:03
    comparing
  • 00:08:03
    and i said that backwards as long as
  • 00:08:05
    you're comparing in the same period it's
  • 00:08:07
    about electronegativity but if you're
  • 00:08:08
    comparing within the same group
  • 00:08:09
    it's about size so that's kind of the
  • 00:08:12
    deal here so you gotta remember which is
  • 00:08:13
    which
  • 00:08:14
    but they're both important but notice
  • 00:08:15
    size must be more important
  • 00:08:17
    because again if you're comparing them
  • 00:08:19
    in the same period
  • 00:08:20
    the more electronegative it is it's a
  • 00:08:22
    weaker base the less electronegative the
  • 00:08:23
    stronger base
  • 00:08:24
    but in the same group the more
  • 00:08:26
    electronegative is actually the stronger
  • 00:08:29
    base
  • 00:08:29
    that's how we know that size must be
  • 00:08:31
    more important consideration
  • 00:08:32
    so but again if you're comparing them in
  • 00:08:34
    the same group it's about size if it's
  • 00:08:35
    in the same
  • 00:08:36
    period it's about electronegativity all
  • 00:08:39
    right
  • 00:08:40
    incidentally so with electronegativity
  • 00:08:42
    you can totally correlate the energy of
  • 00:08:44
    the electrons
  • 00:08:44
    when you have like a negative charge
  • 00:08:46
    let's say they're just lone pairs on a
  • 00:08:47
    more electronegative atom
  • 00:08:49
    on the more electronegative atom it
  • 00:08:50
    pulls them closer to the nucleus which
  • 00:08:51
    lowers their energy and makes them more
  • 00:08:53
    stable in a weaker base
  • 00:08:55
    now in size this is the one place where
  • 00:08:58
    the energy of the electrons does not
  • 00:08:59
    correlate with
  • 00:09:01
    basicity so it turns out the larger atom
  • 00:09:03
    has higher energy electrons
  • 00:09:04
    but it's still the weaker base so
  • 00:09:06
    because it turns out the energy of the
  • 00:09:08
    electrons
  • 00:09:08
    is not the whole story but most of the
  • 00:09:11
    time it's an adequate story but this is
  • 00:09:12
    the one example where it's not
  • 00:09:14
    when you're comparing atoms here in the
  • 00:09:16
    same uh
  • 00:09:17
    group size is more important and instead
  • 00:09:19
    of just worrying about the energy of the
  • 00:09:21
    electrons it's also about the process of
  • 00:09:22
    acting as a base
  • 00:09:23
    of making a new bond to h plus and again
  • 00:09:26
    those big atoms they just make really
  • 00:09:27
    weak bonds to h
  • 00:09:28
    plus and so they're not good bases it
  • 00:09:30
    turns out and so as a result the energy
  • 00:09:32
    the electrons not a good reflection in
  • 00:09:34
    that one
  • 00:09:35
    comparison again comparing different
  • 00:09:37
    atoms
  • 00:09:38
    in the same group but outside of that
  • 00:09:40
    the energy the electrons and
  • 00:09:42
    and will correspond greatly with
  • 00:09:44
    basicity lower energy electrons
  • 00:09:46
    weaker base one exception there
  • 00:09:50
    all right so again bases get stronger as
  • 00:09:52
    we go up the periodic table
  • 00:09:53
    and as we move to the left so if we
  • 00:09:56
    compare some make some comparisons here
  • 00:09:57
    so
  • 00:09:58
    in this case we're going to first
  • 00:10:00
    compare these two and i just want you to
  • 00:10:01
    circle on your
  • 00:10:02
    study guide there which one is the
  • 00:10:04
    stronger base and in this case i can see
  • 00:10:06
    auction is smaller than sulfur they're
  • 00:10:08
    in the same group so it's all about size
  • 00:10:10
    and the smaller base is the stronger
  • 00:10:12
    base
  • 00:10:13
    so we're good to go there and in the
  • 00:10:15
    next pair again circle in the stronger
  • 00:10:16
    base now it's between oxygen and
  • 00:10:18
    nitrogen
  • 00:10:19
    so and now these are in the same period
  • 00:10:21
    so now it's about electronegativity
  • 00:10:23
    oxygen's more electronegative that makes
  • 00:10:24
    him the weaker base nitrogen is less
  • 00:10:26
    electronegative that makes him
  • 00:10:27
    the stronger base in this pair
  • 00:10:32
    cool now at the same breath i also want
  • 00:10:33
    to compare and rank some acids here
  • 00:10:35
    and the problem is is from reo here is
  • 00:10:38
    doesn't this
  • 00:10:39
    doesn't help you rank acids directly the
  • 00:10:42
    rules ario here are going to be for
  • 00:10:43
    ranking
  • 00:10:44
    bases but this is where the idea that
  • 00:10:46
    the stronger acid
  • 00:10:47
    has the weaker conjugate base and vice
  • 00:10:49
    versa comes in handy
  • 00:10:50
    because if you're asked to compare acids
  • 00:10:52
    and that's what i'm asking you over here
  • 00:10:53
    now in these pairs
  • 00:10:55
    what you're actually going to do is look
  • 00:10:56
    back and draw out their conjugate bases
  • 00:10:58
    if you haven't already notice
  • 00:11:00
    this is the conjugate base of this one
  • 00:11:02
    and this is the conjugate base of this
  • 00:11:04
    one
  • 00:11:04
    and so if you're comparing bases that's
  • 00:11:06
    what the rules for you don't want to
  • 00:11:07
    draw any conjugates out or anything like
  • 00:11:08
    that
  • 00:11:09
    but if you're comparing acids first
  • 00:11:12
    thing you'd ever do
  • 00:11:13
    is draw out the conjugate bases and you
  • 00:11:14
    look at them and be like okay who's
  • 00:11:15
    stronger over here
  • 00:11:17
    well he's stronger so if this one is the
  • 00:11:19
    stronger base well then he comes from
  • 00:11:20
    the weaker conjugate acid
  • 00:11:22
    and if this is the weaker base the
  • 00:11:24
    weaker more stable base
  • 00:11:25
    then he comes from the stronger
  • 00:11:28
    conjugate acid
  • 00:11:29
    and so we're not actually ranking the
  • 00:11:30
    acids directly we're only ranking them
  • 00:11:33
    in the context of having
  • 00:11:34
    already ranked their conjugate bases so
  • 00:11:37
    when you're asked to rank bases
  • 00:11:38
    good to go that's what the rules are for
  • 00:11:40
    but when you're asked to rank acids
  • 00:11:41
    you're going to do it indirectly every
  • 00:11:42
    time
  • 00:11:43
    so well almost every time so but you're
  • 00:11:45
    going to do it indirectly most of the
  • 00:11:46
    time
  • 00:11:47
    by looking at the conjugate bases
  • 00:11:48
    instead same thing here so here we
  • 00:11:50
    circle the stronger base
  • 00:11:52
    and if this is the stronger base it has
  • 00:11:53
    the weaker conjugate acid
  • 00:11:56
    so if this was the weaker base he has
  • 00:11:57
    the stronger
  • 00:11:59
    conjugate acid and so a lot of times
  • 00:12:01
    when we're ranking acids we just say
  • 00:12:02
    okay which one of these has the weaker
  • 00:12:04
    more stable conjugate base
  • 00:12:06
    in this case it was sulfur and in these
  • 00:12:08
    two if i said which one again has the
  • 00:12:09
    weaker
  • 00:12:10
    more stable conjugate base in this case
  • 00:12:11
    it was oxygen now up here it was the
  • 00:12:13
    weaker conjugate base because sulfur is
  • 00:12:15
    bigger than oxygen
  • 00:12:16
    and down here so the weaker more stable
  • 00:12:19
    conjugate base was oxygen because oxygen
  • 00:12:21
    is more electronegative
  • 00:12:22
    than nitrogen cool that is your
  • 00:12:26
    atom rule all right so after atom is the
  • 00:12:29
    resonance rule and again these rules for
  • 00:12:32
    ranking bases and resonance simply
  • 00:12:34
    stabilizes bases that's the way it works
  • 00:12:36
    so if you have something with resonance
  • 00:12:37
    and something without
  • 00:12:38
    well the thing with resin is generally
  • 00:12:39
    going to be more stable assuming you've
  • 00:12:42
    already done your atom rule so again
  • 00:12:43
    we would never start out with the
  • 00:12:44
    resonance rule we first verify that the
  • 00:12:46
    bases we're comparing all have the same
  • 00:12:47
    charge
  • 00:12:48
    then we verify that they're all the same
  • 00:12:50
    atom acting as the base and then we'd
  • 00:12:52
    move on to resonance so
  • 00:12:53
    if we look at the example here we're
  • 00:12:54
    going to compare these three bases and
  • 00:12:56
    i've drawn out all the resonance
  • 00:12:58
    structures here and so
  • 00:12:59
    in this case the first question would be
  • 00:13:00
    do they have the same charge well
  • 00:13:01
    negative charge negative charge negative
  • 00:13:03
    charge
  • 00:13:03
    done cool then we move on to the atom
  • 00:13:05
    rule and say which atom actually acts as
  • 00:13:07
    the base well it's oxygen here
  • 00:13:09
    it's oxygen here and it's oxygen here
  • 00:13:12
    and so we have a tie and so then we'd
  • 00:13:15
    have to move on and go to the resonance
  • 00:13:17
    rule so that's kind of how this works
  • 00:13:19
    so you wouldn't start with the resonance
  • 00:13:20
    rule unless you've already done the
  • 00:13:21
    charge in the atom rule first
  • 00:13:23
    all right so doing the resonance rule
  • 00:13:24
    now we see that here the negative charge
  • 00:13:26
    is
  • 00:13:27
    no resonance it's on a single oxygen
  • 00:13:29
    completely here
  • 00:13:30
    the negative charge due to resonance is
  • 00:13:32
    shared between two oxygen atoms that
  • 00:13:33
    makes it more
  • 00:13:34
    stable and a more stable base is a
  • 00:13:36
    weaker base this is a weaker base than
  • 00:13:38
    the first one that has no resonance
  • 00:13:40
    and then finally this last one the
  • 00:13:41
    negative charge is actually shared on
  • 00:13:43
    three oxygen atoms and is even more
  • 00:13:46
    stable and even more stable means even
  • 00:13:49
    weaker base
  • 00:13:50
    and so if we were to rank these as bases
  • 00:13:52
    with one being the strongest and
  • 00:13:54
    three being the weakest well our most
  • 00:13:55
    stable base is our
  • 00:13:57
    weakest base and let's do this in blue
  • 00:14:01
    so and then our strongest base that had
  • 00:14:02
    no resonance number one and then
  • 00:14:04
    obviously
  • 00:14:04
    this one that had two resonant
  • 00:14:06
    structures sharing on two auctions was
  • 00:14:07
    number two
  • 00:14:09
    now something you should know about
  • 00:14:10
    comparing resonance it's not just about
  • 00:14:12
    the total number of resonance structures
  • 00:14:14
    it's also about the quality of resonance
  • 00:14:16
    structures because if you notice like
  • 00:14:17
    here
  • 00:14:18
    i'm sharing the negative charge on two
  • 00:14:20
    oxygens and here it's on three options
  • 00:14:22
    well that's an easy comparison
  • 00:14:23
    but what if the negative charge was
  • 00:14:24
    shared like instead of on two auctions
  • 00:14:26
    what if it was shared on one auction and
  • 00:14:28
    three carbons well carbon's not as
  • 00:14:30
    electronegative as oxygen
  • 00:14:31
    it's not as good of a place to put a
  • 00:14:33
    negative charge
  • 00:14:34
    so you gotta ask yourself is it two
  • 00:14:36
    resonant structures sharing it on two
  • 00:14:38
    oxygens better
  • 00:14:38
    or is four resonant structures but it's
  • 00:14:40
    only one oxygen and three carbons better
  • 00:14:43
    well i don't expect you to know that
  • 00:14:44
    well it turns out sharing it on two
  • 00:14:45
    auctions
  • 00:14:46
    is better so but again that's one of
  • 00:14:49
    those
  • 00:14:49
    examples where you're just kind of until
  • 00:14:51
    you've seen it worked out for you but
  • 00:14:52
    you just don't know however that's
  • 00:14:54
    exactly the situation we have when it
  • 00:14:56
    compare
  • 00:14:56
    carboxylic acid to a phenol but if
  • 00:14:59
    you've memorized your pkas you'd know
  • 00:15:01
    that a carboxylic acid has a pka of 4-5
  • 00:15:04
    a phenol has a pka of 10 so the
  • 00:15:06
    carboxylic acid is stronger
  • 00:15:08
    and you wouldn't have to rely on the
  • 00:15:09
    rules for an example that's a little bit
  • 00:15:11
    challenging
  • 00:15:12
    because you've memorized some pkas so
  • 00:15:14
    just want to point
  • 00:15:15
    out where that might come in handy okay
  • 00:15:18
    so here's
  • 00:15:19
    we've ranked some bases now what if i
  • 00:15:20
    asked you to rank these
  • 00:15:22
    acids and so for these acids notice
  • 00:15:24
    these are just the conjugate
  • 00:15:26
    acids here and if you were asked to rank
  • 00:15:28
    these acids
  • 00:15:29
    first thing you'd want to do is draw the
  • 00:15:31
    conjugate bases if you didn't have them
  • 00:15:33
    already on the board like i do
  • 00:15:34
    so we've got them on the board now and
  • 00:15:36
    in this case you just know that the
  • 00:15:38
    acids have the exact
  • 00:15:39
    opposite ranking so the strongest acid
  • 00:15:42
    has the weakest conjugate base
  • 00:15:44
    well the weakest conjugate base was this
  • 00:15:45
    one it was the one that was most stable
  • 00:15:47
    due to resonance the weakest base so
  • 00:15:49
    then this must be the strongest
  • 00:15:51
    acid we'll make him number one
  • 00:15:55
    and it's just the exact opposite ranking
  • 00:15:58
    our strongest and least stable base
  • 00:16:02
    comes from the weakest conjugate acid
  • 00:16:04
    cool
  • 00:16:06
    so once again you can rank bases
  • 00:16:08
    directly that's what the
  • 00:16:09
    reo mnemonic and the rules are for but
  • 00:16:12
    acids we rank
  • 00:16:13
    indirectly by looking at the conjugate
  • 00:16:15
    bases and just knowing again the
  • 00:16:16
    stronger the acid the weaker the
  • 00:16:18
    conjugate base
  • 00:16:18
    and vice versa all right the next rule
  • 00:16:21
    in our reo mnemonic is
  • 00:16:23
    induction so an induction deals with
  • 00:16:26
    polarity
  • 00:16:27
    now for now i'm going to look at things
  • 00:16:29
    that are simply electronegative
  • 00:16:30
    we like to call them electron
  • 00:16:32
    withdrawing when they're electronegative
  • 00:16:34
    because they're pulling electrons away
  • 00:16:35
    and if you recall
  • 00:16:36
    we talked about charge at the very
  • 00:16:38
    beginning we said that something with a
  • 00:16:39
    more negative charge is a stronger base
  • 00:16:41
    whereas with a less negative charge i.e
  • 00:16:43
    more positive charge would be a
  • 00:16:45
    weaker base and so what an
  • 00:16:46
    electronegative atom does is it pulls
  • 00:16:47
    electron density away from a base
  • 00:16:50
    making the base less negative and
  • 00:16:52
    therefore more stable
  • 00:16:54
    lower energy electrons and a weaker base
  • 00:16:57
    cool we'll find out later on in the
  • 00:16:58
    course not in this chapter that
  • 00:17:00
    in addition to electron withdrawing
  • 00:17:01
    groups there are also things called
  • 00:17:03
    electron
  • 00:17:03
    donating groups and they're not going to
  • 00:17:05
    really have much relevance here
  • 00:17:07
    but they will have some relevance down
  • 00:17:09
    usually in the beginning a second
  • 00:17:11
    semester when you study alcohols and
  • 00:17:12
    phenols
  • 00:17:15
    all right so let's go through our list
  • 00:17:17
    and again we wouldn't ever start with
  • 00:17:19
    induction as a rule we just work our way
  • 00:17:21
    down
  • 00:17:21
    so first thing i want to look at in
  • 00:17:23
    comparing the first pair here i want you
  • 00:17:24
    to circle the stronger pair
  • 00:17:26
    or the stronger base in the pair is
  • 00:17:28
    charge well they're both negative one
  • 00:17:29
    then go to atom well oxygen is the base
  • 00:17:33
    in either case the atom with the
  • 00:17:35
    negative charge so no difference there
  • 00:17:37
    so then we move on to resonance well
  • 00:17:38
    these are both the conjugate bases of
  • 00:17:40
    carboxylic acids
  • 00:17:41
    they're both going to have two resonant
  • 00:17:42
    structures and share the negative charge
  • 00:17:45
    between two oxygens we still have no
  • 00:17:47
    distinguishing difference
  • 00:17:49
    and so now we move on to induction and
  • 00:17:52
    so
  • 00:17:52
    we've already identified that oxygen is
  • 00:17:54
    the base that's the atom rule don't get
  • 00:17:56
    that confused a lot of students confuse
  • 00:17:57
    the atom rule in the induction rule
  • 00:17:59
    my question now is now that we know
  • 00:18:00
    oxygen is the base in both cases
  • 00:18:03
    are there any electronegative atoms
  • 00:18:05
    nearby that can act as a helpful
  • 00:18:07
    neighbor to help stabilize the base
  • 00:18:10
    and over here we've got chlorine and
  • 00:18:11
    over here there's nobody electronegative
  • 00:18:13
    around those auctions at all so again
  • 00:18:15
    those options are sharing the negative
  • 00:18:17
    charge by resonance
  • 00:18:18
    they are the base and if you are the
  • 00:18:20
    base that's what the atom rule's about
  • 00:18:22
    and the atom rules about size and then
  • 00:18:24
    electronegativity
  • 00:18:26
    but induction here means you're not the
  • 00:18:28
    base you're just a helpful neighbor
  • 00:18:30
    and you're in the area to help that base
  • 00:18:33
    out
  • 00:18:33
    and it has nothing to do with size it
  • 00:18:35
    has everything to do with just pure
  • 00:18:37
    electronegativity
  • 00:18:38
    pure polarity if you will and so in this
  • 00:18:41
    case
  • 00:18:41
    the chlorine here is going to pull
  • 00:18:43
    electron density
  • 00:18:44
    so away from this carbon technically
  • 00:18:48
    which is then going to pull it away from
  • 00:18:49
    this carbon which then pulls away from
  • 00:18:50
    this carbon
  • 00:18:51
    which is then going to pull some away
  • 00:18:52
    from those oxygens eventually making
  • 00:18:54
    those
  • 00:18:54
    oxygens less negatively charged which
  • 00:18:57
    makes them more stable lower energy and
  • 00:18:59
    a weaker base so the one stabilized by
  • 00:19:02
    induction
  • 00:19:03
    is the weaker base okay so that's the
  • 00:19:06
    first part
  • 00:19:07
    so and again induction is all about
  • 00:19:09
    electronegativity so far as we're
  • 00:19:11
    concerned with in this lesson
  • 00:19:13
    all right in the next example here so
  • 00:19:16
    we're going to go through the rules
  • 00:19:17
    again charge no difference atom
  • 00:19:19
    oxygen in both cases no difference
  • 00:19:21
    resonance stabilized by resonance
  • 00:19:23
    between two auctions in both cases no
  • 00:19:25
    difference so we make it to induction
  • 00:19:27
    and we ask do either of these have a
  • 00:19:29
    helpful neighbor nearby
  • 00:19:30
    well yeah they both do and they have the
  • 00:19:33
    same neighbor
  • 00:19:34
    chlorine which is equal in
  • 00:19:36
    electronegativity so however
  • 00:19:38
    if you notice by the way the we pull
  • 00:19:40
    electrons
  • 00:19:41
    from the adjacent atom through the bonds
  • 00:19:43
    based on electronegativity
  • 00:19:44
    so if we were like a hundred carbons
  • 00:19:47
    long and then there was just a chlorine
  • 00:19:48
    way over here
  • 00:19:49
    do you think the other side of the
  • 00:19:50
    molecule would even know there's a
  • 00:19:51
    chlorine down there no
  • 00:19:52
    and so proximity is really important as
  • 00:19:54
    well typically the closer it is
  • 00:19:56
    the bigger the impact it's going to have
  • 00:19:58
    in terms of stabilization so
  • 00:20:00
    in this case the chlorine is closer to
  • 00:20:02
    these oxygens it's only one
  • 00:20:04
    two and then three bonds away whereas
  • 00:20:06
    this one is one two
  • 00:20:07
    three four bonds away from the oxygens
  • 00:20:10
    and so the closer it is the more
  • 00:20:11
    stabilizing of an impact
  • 00:20:13
    the greater its stabilization due to
  • 00:20:15
    induction
  • 00:20:16
    and so that makes this the more stable
  • 00:20:18
    base and the more is the weaker
  • 00:20:20
    base so the one that's less stabilized
  • 00:20:22
    is the stronger base
  • 00:20:25
    all right so now we've learned having an
  • 00:20:27
    electronegative atom
  • 00:20:28
    in the area is helpful and the closer it
  • 00:20:31
    is the more helpful it is
  • 00:20:32
    and so now what if we have two different
  • 00:20:35
    helpful neighbors
  • 00:20:37
    uh carrying out inductive stabilization
  • 00:20:39
    here so once again
  • 00:20:40
    charge no difference atom auction
  • 00:20:43
    auction no difference resonance shared
  • 00:20:46
    between two oxygen two resonant
  • 00:20:47
    structures on both no difference
  • 00:20:49
    so then we make it to induction and now
  • 00:20:51
    there is a difference now they're in the
  • 00:20:52
    same location they're the same distance
  • 00:20:54
    away from the oxygens from the bases
  • 00:20:56
    but one's chlorine and one's fluorine
  • 00:20:58
    and this is the most one of the most
  • 00:20:59
    common mistakes students make
  • 00:21:00
    is they say okay but chad you just told
  • 00:21:03
    me that fluorine was a better base than
  • 00:21:04
    chlorine
  • 00:21:05
    no no no i told you when fluorine is
  • 00:21:08
    the base is the atom acting as the base
  • 00:21:11
    that it's a better base
  • 00:21:12
    but again here fluorine and chlorine
  • 00:21:14
    they're not the base in either one of
  • 00:21:15
    these
  • 00:21:16
    the oxygens have the negative charge
  • 00:21:18
    they're the base
  • 00:21:19
    fluorine and chlorine are not acting as
  • 00:21:21
    the base at all but they can help
  • 00:21:22
    stabilize the oxygens who are acting as
  • 00:21:24
    the base
  • 00:21:25
    and again your ability to help stabilize
  • 00:21:27
    those auctions has
  • 00:21:28
    nothing to do with how big you are only
  • 00:21:32
    with how electronegative you are and
  • 00:21:33
    fluorine is more electronegative than
  • 00:21:35
    chlorine
  • 00:21:36
    and as fluorine is more electronegative
  • 00:21:37
    than chlorine this will be a more
  • 00:21:39
    stabilized base that negative charge
  • 00:21:41
    will be diminished more on these
  • 00:21:42
    auctions than on the auctions on the
  • 00:21:44
    molecule next door
  • 00:21:45
    and so as a result the more stable base
  • 00:21:46
    on the right here is the weaker base
  • 00:21:49
    more stabilized by induction so the one
  • 00:21:51
    on the left
  • 00:21:52
    is the stronger base cool can't
  • 00:21:55
    emphasize this enough though
  • 00:21:57
    so the difference between the atom rule
  • 00:21:58
    and induction the atom rule
  • 00:22:00
    is you're examining the atom that's
  • 00:22:02
    acting as the base
  • 00:22:03
    which in our case was oxygens in both
  • 00:22:05
    cases no difference
  • 00:22:07
    induction though is you're looking for a
  • 00:22:09
    helpful neighbor who's near to the base
  • 00:22:12
    and it's all about electronegativity so
  • 00:22:14
    the atom rule is about size first and
  • 00:22:16
    then electronegativity are you the base
  • 00:22:18
    then we're going to talk about your size
  • 00:22:20
    and then your electronegativity but if
  • 00:22:21
    we're talking about induction and you're
  • 00:22:23
    not the base you're just nearby you're
  • 00:22:24
    in the neighborhood
  • 00:22:25
    it's purely about your electronegativity
  • 00:22:27
    your size is irrelevant
  • 00:22:31
    all right finally last example here and
  • 00:22:33
    in this case same comparisons same
  • 00:22:35
    charge same atom same resonance
  • 00:22:36
    comes down to induction again and two
  • 00:22:39
    fluorines
  • 00:22:40
    is better than one so to speak so two
  • 00:22:42
    fluorines two electronegative atoms will
  • 00:22:44
    have even more of a stabilizing
  • 00:22:45
    impact than one flooring so this will be
  • 00:22:48
    the even more stable base and therefore
  • 00:22:49
    the weaker base
  • 00:22:50
    therefore this one is the stronger base
  • 00:22:54
    cool so now i've given you an example of
  • 00:22:55
    every kind of comparison you might see
  • 00:22:57
    and again we only compared two at a time
  • 00:22:59
    you might get three or four of these and
  • 00:23:00
    be asked to rank them in order well
  • 00:23:02
    everything that's important just came up
  • 00:23:04
    do you have
  • 00:23:04
    an electron you know withdrawing group
  • 00:23:06
    and one doesn't do you have
  • 00:23:08
    both the same electronic group but one's
  • 00:23:09
    closer and one's further or do you have
  • 00:23:11
    two different ones and one's more
  • 00:23:12
    electronegative one's less less or
  • 00:23:13
    negative
  • 00:23:13
    or do you have more electron withdrawing
  • 00:23:15
    groups versus another
  • 00:23:17
    those are the typical comparisons you're
  • 00:23:18
    likely to see okay
  • 00:23:20
    so i didn't want to clutter up the board
  • 00:23:21
    initially so but in addition to
  • 00:23:22
    comparing these lovely bases
  • 00:23:24
    now we're going to go compare their
  • 00:23:26
    conjugate acids
  • 00:23:27
    and again the key is again the rules are
  • 00:23:29
    for bases and we just jumped right into
  • 00:23:31
    comparing the bases
  • 00:23:32
    but if you had been asked to compare any
  • 00:23:34
    of these pairs of conjugate acids
  • 00:23:35
    first instead well the first thing to
  • 00:23:37
    realize is like oh they're asking me to
  • 00:23:38
    compare acids i don't compare acids
  • 00:23:40
    i would draw out their conjugate bases
  • 00:23:42
    and then compare those
  • 00:23:43
    and fortunately we can already take
  • 00:23:44
    advantage of the fact that we've done
  • 00:23:46
    that
  • 00:23:47
    and so we're already ready to compare
  • 00:23:48
    these because we've already compared the
  • 00:23:49
    conjugate bases
  • 00:23:50
    and so in this case in the first example
  • 00:23:53
    in these two conjugate acids i would
  • 00:23:54
    again draw out their conjugate bases
  • 00:23:56
    i'd realize that this one is the more
  • 00:23:58
    stable conjugate base the more stable
  • 00:24:00
    conjugate base is the weaker conjugate
  • 00:24:01
    base
  • 00:24:02
    and the more stable weaker conjugate
  • 00:24:03
    base comes from the
  • 00:24:05
    stronger conjugate acid so now we're
  • 00:24:08
    circling the stronger conjugate acid
  • 00:24:09
    same thing in the next example
  • 00:24:11
    we already figured out again in
  • 00:24:12
    comparing these two acids we already
  • 00:24:14
    figured out the relative
  • 00:24:15
    basicities of the conjugate bases so
  • 00:24:18
    this had the chlorine closer
  • 00:24:19
    which had a more stabilizing influence
  • 00:24:21
    by induction and the more stable base is
  • 00:24:23
    the weaker base and the weaker base
  • 00:24:25
    comes from the
  • 00:24:26
    stronger conjugate acid cool next
  • 00:24:30
    comparison again we're comparing these
  • 00:24:31
    two acids first thing you do is draw
  • 00:24:33
    these two conjugate bases and here
  • 00:24:35
    fluorine was more electronegative than
  • 00:24:36
    chlorine
  • 00:24:37
    and so fluorine is going to pull more
  • 00:24:38
    electrons away from the oxygens
  • 00:24:40
    making them less negative and more
  • 00:24:42
    stable and more stable means weaker base
  • 00:24:43
    and the weaker base again comes from the
  • 00:24:46
    stronger conjugate acid and finally in
  • 00:24:50
    the last example we found out that
  • 00:24:51
    two fluorines was more stabilizing than
  • 00:24:53
    one fluorine so this was the more stable
  • 00:24:54
    base
  • 00:24:55
    the more stable base comes once again
  • 00:24:58
    from the
  • 00:24:58
    stronger conjugate acid
  • 00:25:02
    cool so obviously very fortunate that we
  • 00:25:05
    already had the conjugate bases on the
  • 00:25:07
    board and we already had them ranked
  • 00:25:09
    but if we hadn't that would have been
  • 00:25:10
    the first thing we'd have to do
  • 00:25:12
    so the last rule in our mnemonic is
  • 00:25:14
    orbital so the o here and
  • 00:25:16
    once again you wouldn't just jump into
  • 00:25:18
    using this rule you'd first have to
  • 00:25:19
    verify that
  • 00:25:20
    there's no distinction made between the
  • 00:25:21
    rest of the rules and the comparison
  • 00:25:22
    that you're making
  • 00:25:24
    so and again it's orbitals here if the o
  • 00:25:25
    for orbitals but again it really refers
  • 00:25:27
    to a difference in the hybridization
  • 00:25:29
    of your basic atom so if we take a look
  • 00:25:32
    here at comparing these three
  • 00:25:34
    lovely bases here first thing we do is
  • 00:25:36
    say do they all have the same charge yep
  • 00:25:38
    negative one negative one negative one
  • 00:25:40
    okay no difference there then we move on
  • 00:25:41
    to talk about the basic atom and it's
  • 00:25:43
    carbon compared to carbon compared to
  • 00:25:45
    carbon
  • 00:25:46
    okay atom rule doesn't help us either so
  • 00:25:48
    we'd move on to resonance
  • 00:25:49
    and it turns out none of these are
  • 00:25:51
    stabilized by resonance so if you look
  • 00:25:53
    you might go chad wait a minute load
  • 00:25:54
    about like this guy
  • 00:25:55
    well again when your lone pair of
  • 00:25:56
    electrons is exactly one bond away from
  • 00:25:58
    the pi electrons ie like allilic or
  • 00:26:01
    benzylic
  • 00:26:01
    that's when you can expect resonance but
  • 00:26:03
    here it's not one bond away it's right
  • 00:26:04
    where the pi electrons are so no
  • 00:26:07
    resonance in any of these
  • 00:26:08
    so move on to induction are there any
  • 00:26:10
    electronegative atoms in the area to
  • 00:26:11
    help stabilize this
  • 00:26:12
    nope not in any of the cases so finally
  • 00:26:15
    we move on to orbitals and we say is
  • 00:26:18
    there a difference in the hybridization
  • 00:26:19
    of the basic atom in all these cases and
  • 00:26:22
    there is indeed a difference so this
  • 00:26:23
    carbon right here is only two electron
  • 00:26:25
    domains
  • 00:26:25
    it's bonded to one atom and has one lone
  • 00:26:27
    pair so
  • 00:26:28
    it's going to be sp hybridized so this
  • 00:26:31
    carbon right here
  • 00:26:33
    is bonded to two atoms a carbon and a
  • 00:26:34
    hydrogen maybe i'll draw that hydrogen
  • 00:26:36
    in to make this a little more obvious
  • 00:26:38
    so it bonded to two atoms one lone pair
  • 00:26:40
    three electron domains
  • 00:26:42
    sp2 hybridized and then finally this one
  • 00:26:45
    right here is bonded to three atoms a
  • 00:26:46
    carbon two hydrogens and it has a lone
  • 00:26:48
    pair four domains is going to be sp3
  • 00:26:51
    hybridized
  • 00:26:53
    so there is a difference in
  • 00:26:54
    hybridization and it turns out that's a
  • 00:26:56
    significant thing now
  • 00:26:57
    if you kind of look at the difference
  • 00:26:58
    between an sp and sp2 and sp3
  • 00:27:00
    so your sp is 50 s 50
  • 00:27:04
    p we'd say 50 s character and
  • 00:27:07
    probably looks like something like this
  • 00:27:09
    your sp2 is now only 33 percent s one
  • 00:27:12
    third s
  • 00:27:13
    two thirds p and resembling more like a
  • 00:27:16
    p orbital now only 33
  • 00:27:18
    s character it's a little longer and the
  • 00:27:21
    electrons are going to be a little
  • 00:27:22
    further from the nucleus at the node
  • 00:27:23
    there than they would be if they were
  • 00:27:25
    not sp hybrid orbital
  • 00:27:26
    so having a lone pair and an sp as
  • 00:27:28
    compared to having a lone pair in an sp2
  • 00:27:30
    they're going to be on average closer to
  • 00:27:32
    the nucleus in an sp hybrid than an sp2
  • 00:27:35
    and then finally in an sp3 hybrid
  • 00:27:37
    orbital
  • 00:27:39
    it's even elongated even further and so
  • 00:27:42
    the electrons on average are going to be
  • 00:27:43
    even further from the nucleus and be
  • 00:27:45
    even
  • 00:27:45
    higher energy and less stable in an sp3
  • 00:27:48
    and so the idea then is that your lone
  • 00:27:50
    pair is going to be most stable
  • 00:27:52
    on an sp hybridized carbon as compared
  • 00:27:54
    to an sp2 or an sp3
  • 00:27:55
    and if here it's most stable that makes
  • 00:27:58
    him the weakest
  • 00:27:59
    base which we'll put number three in
  • 00:28:02
    this case
  • 00:28:03
    and then here on the sp3 hybridized atom
  • 00:28:05
    that lone pair is going to be the least
  • 00:28:07
    stable which in our case is going to
  • 00:28:08
    mean the strongest space and then this
  • 00:28:10
    guy's in the middle
  • 00:28:11
    and so that's our trend for basicity
  • 00:28:13
    that's the orbital rule really a
  • 00:28:14
    difference in hybridization and so if
  • 00:28:16
    you were
  • 00:28:17
    asked to compare the conjugate acids
  • 00:28:19
    instead well again you'd realize that
  • 00:28:21
    i'm not comparing acids
  • 00:28:22
    and first thing you do is draw out all
  • 00:28:23
    the conjugate bases go through the rules
  • 00:28:25
    and come up with this relative basicity
  • 00:28:28
    which would then allow you to come up
  • 00:28:29
    with exactly the opposite trend
  • 00:28:32
    in acidity for the conjugate acids so
  • 00:28:35
    the most stable and weakest conjugate
  • 00:28:37
    base
  • 00:28:37
    has the strongest conjugate acid so on
  • 00:28:41
    and so forth this rule doesn't come up
  • 00:28:44
    very often
  • 00:28:45
    but it is something you're probably
  • 00:28:46
    going to see at least once or twice
  • 00:28:48
    between your homeworks and your tests
  • 00:28:50
    so now we've made it completely through
  • 00:28:51
    the mnemonic and we've kind of gone step
  • 00:28:53
    by step and
  • 00:28:54
    you know we kind of knew what
  • 00:28:55
    comparisons were coming because we were
  • 00:28:56
    going in order so now i want to work
  • 00:28:58
    three examples and with these three
  • 00:29:01
    examples we're going to do
  • 00:29:01
    specifically comparing acidity so and
  • 00:29:04
    we're going to keep in mind the pkas
  • 00:29:06
    we're supposed to know as well as all
  • 00:29:07
    these lovely rules
  • 00:29:09
    all right so we've got three different
  • 00:29:10
    comparisons here and the first one's
  • 00:29:12
    going to be
  • 00:29:13
    this lovely species versus this one and
  • 00:29:15
    first thing you should do is keep in
  • 00:29:16
    mind what pkas do you know well
  • 00:29:18
    this is a carboxylic acid and his pka
  • 00:29:21
    is in the four to five range usually
  • 00:29:23
    it's pretty typical
  • 00:29:24
    whereas this is an alcohol and its pka
  • 00:29:27
    is usually in the range of like 16.
  • 00:29:29
    now the truth is this one's got a
  • 00:29:31
    chlorine that's going to inductively
  • 00:29:32
    stabilize the conjugate base
  • 00:29:34
    which is going to ultimately make the
  • 00:29:35
    conjugate base weaker and this acid a
  • 00:29:37
    stronger acid
  • 00:29:38
    but 16 versus four to five it's not
  • 00:29:40
    going to make it down that low
  • 00:29:42
    not a chance and so in this case
  • 00:29:44
    technically you could just be like yeah
  • 00:29:46
    there's my stronger acid i circled it
  • 00:29:48
    life is good so
  • 00:29:50
    but if you didn't you know recall your
  • 00:29:52
    pkas or didn't categorize these
  • 00:29:53
    correctly again
  • 00:29:54
    you could always just draw their
  • 00:29:55
    conjugate bases and be like
  • 00:29:59
    and use your reo mnemonic here so in
  • 00:30:02
    this case
  • 00:30:05
    you go through and say do they have the
  • 00:30:06
    same charge yep negative one negative
  • 00:30:08
    one for comparing your bases
  • 00:30:09
    then you'd say okay adam rule auction's
  • 00:30:12
    the base and
  • 00:30:12
    auction's the base it's a tie adam rule
  • 00:30:15
    didn't help me so move on to the
  • 00:30:16
    resonance rule
  • 00:30:17
    and we'd see that the one on the left
  • 00:30:18
    has resonance and the one on the right
  • 00:30:20
    does not have resonance
  • 00:30:22
    and so the one with resonance is more
  • 00:30:24
    stable and a more stable base is a
  • 00:30:25
    weaker base and a weaker base
  • 00:30:26
    comes from the stronger conjugate acid
  • 00:30:29
    the rules would have led us to the same
  • 00:30:30
    place
  • 00:30:32
    cool moving on to the next one here and
  • 00:30:33
    this is one i brought up earlier so
  • 00:30:35
    we've got a carboxylic acid here and
  • 00:30:37
    again
  • 00:30:37
    pka of a typical carboxylic acid is in
  • 00:30:39
    the four to five range and
  • 00:30:41
    this is a phenol and pka of a typical
  • 00:30:42
    phenol is in the 10 range
  • 00:30:44
    and so we can say yep we've got our
  • 00:30:47
    stronger acid right here because we
  • 00:30:49
    memorized some pkas
  • 00:30:50
    now this is the tricky one had you not
  • 00:30:53
    memorized those pkas
  • 00:30:55
    you'd had a tough time with this one
  • 00:30:56
    until you came across it somewhere along
  • 00:30:58
    the way
  • 00:30:59
    and we've seen a carboxylic acid it's
  • 00:31:01
    got two resonant structures shares the
  • 00:31:04
    negative charge
  • 00:31:07
    on two oxygen atoms here but the phenol
  • 00:31:10
    we haven't actually drawn out
  • 00:31:11
    specifically but the conjugate base
  • 00:31:16
    actually shares the negative charge
  • 00:31:18
    between the auction and then it turns
  • 00:31:20
    out
  • 00:31:20
    three of the carbon atoms in the ring
  • 00:31:28
    i'm going to draw these out but i'm not
  • 00:31:30
    going to actually show you how to get
  • 00:31:31
    there
  • 00:31:32
    i'll leave that on you for now
  • 00:31:38
    and finally one more
  • 00:31:49
    you know what i'm going to be a little
  • 00:31:50
    nicer than i said i was going to be so
  • 00:31:52
    and here lone pair comes down low pair
  • 00:31:57
    comes out onto that atom
  • 00:31:59
    here lone pair goes into form a pi bond
  • 00:32:00
    pi bond becomes a lone pair getting you
  • 00:32:02
    here
  • 00:32:03
    here lone pair becomes a pi bond pi bond
  • 00:32:05
    becomes a lone pair
  • 00:32:06
    getting you here all right so the
  • 00:32:09
    question got to ask yourself a lot of
  • 00:32:10
    students get this one wrong because here
  • 00:32:11
    they're all more resonant structures
  • 00:32:13
    more resonance more stable base more
  • 00:32:14
    stable based weaker base weaker base
  • 00:32:15
    comes from the stronger acid but we saw
  • 00:32:17
    that wasn't the case at all
  • 00:32:18
    but we're not comparing apples to apples
  • 00:32:20
    here so you can't just compare the
  • 00:32:21
    absolute number of resonance structures
  • 00:32:23
    unless the negative charge is just being
  • 00:32:24
    shared on the same atom every time well
  • 00:32:26
    that would
  • 00:32:26
    that would work so but here sharing the
  • 00:32:28
    negative charge on two options
  • 00:32:30
    as compared to sharing the negative
  • 00:32:31
    charge on one action and
  • 00:32:33
    three carbons and there's no intuitive
  • 00:32:35
    way to just be like well i have a hunch
  • 00:32:37
    so it really does come down to either
  • 00:32:38
    having seen this example before
  • 00:32:40
    or just knowing those pkas super helpful
  • 00:32:44
    in this case it turns out sharing it on
  • 00:32:45
    two auctions was more stable that was
  • 00:32:46
    the weaker base
  • 00:32:47
    which came from our stronger acid all
  • 00:32:50
    right finally this last one
  • 00:32:52
    this last one is a super tricky example
  • 00:32:54
    but you might remember pka's here and
  • 00:32:55
    pka of a terminal alkyne here
  • 00:32:57
    was right around 26. so
  • 00:33:01
    and we didn't cover this guy's pka
  • 00:33:03
    explicitly but we did cover a very
  • 00:33:04
    similar molecule
  • 00:33:06
    and that similar molecule was ammonia
  • 00:33:08
    and we said ammonius pka
  • 00:33:10
    was right around 38. and so whether you
  • 00:33:13
    deprotonate neutral nitrogen ammonia or
  • 00:33:15
    a neutral nitrogen on
  • 00:33:17
    an amine it's going to be around a pka
  • 00:33:19
    of 38
  • 00:33:20
    and i can see that my lower pka is
  • 00:33:22
    definitely this guy
  • 00:33:23
    and he's going to be our stronger acid
  • 00:33:27
    cool and i brought this one up on
  • 00:33:28
    purpose because this is a tricky example
  • 00:33:30
    if you try to follow the mnemonic here
  • 00:33:32
    you're going to get hosed
  • 00:33:33
    and let's see why so if we draw those
  • 00:33:36
    conjugate bases
  • 00:33:46
    so said at the beginning of this lesson
  • 00:33:48
    that there's no perfect set of rules
  • 00:33:50
    because there are always exceptions like
  • 00:33:51
    this
  • 00:33:52
    one so if we look here and we start with
  • 00:33:54
    charge like negative one negative one
  • 00:33:55
    life is good so we move on to atom we're
  • 00:33:57
    like carbon versus
  • 00:33:59
    nitrogen well carbon and nitrogen are in
  • 00:34:01
    the same
  • 00:34:02
    period which means it's going to be
  • 00:34:04
    about electronegativity
  • 00:34:05
    and as nitrogen is more electronegative
  • 00:34:07
    we'd think oh more electronegative
  • 00:34:09
    more stable more stable base weaker base
  • 00:34:11
    weaker base comes from the stronger acid
  • 00:34:13
    and we totally got the opposite
  • 00:34:15
    determination from our pka values that
  • 00:34:17
    we knew
  • 00:34:18
    so what's going on here so well it turns
  • 00:34:20
    out this is usually the order of
  • 00:34:22
    priority as far as it
  • 00:34:24
    you know what distinguishes two bases
  • 00:34:26
    and comparing them
  • 00:34:27
    and order importance so however so
  • 00:34:31
    there's two differences here it is a
  • 00:34:32
    difference in atom but it's also a
  • 00:34:33
    difference in hybridization of the
  • 00:34:35
    orbitals
  • 00:34:36
    so it's not just comparing carbon to
  • 00:34:37
    nitrogen and that's the only difference
  • 00:34:39
    it's an sp hybridized carbon versus an
  • 00:34:41
    sp3 hybridized nitrogen
  • 00:34:44
    and it just so turns out that the sp
  • 00:34:47
    so is more stable the sp carbon is more
  • 00:34:50
    stable than the sp3 nitrogen
  • 00:34:53
    now there's no intuitive way to have
  • 00:34:54
    known that but because we knew the pkas
  • 00:34:57
    we didn't get hosed by this exception
  • 00:34:59
    from our rules
  • 00:35:00
    so like i said there's usually two or
  • 00:35:02
    three comparisons you can make
  • 00:35:03
    where the rules are going to lead you
  • 00:35:05
    astray but if you know all your pkas
  • 00:35:07
    those can't get you cool this is asked
  • 00:35:10
    in bases and ranking them
  • 00:35:12
    and again understanding relative acidity
  • 00:35:14
    and basically basicity is really going
  • 00:35:16
    to be key
  • 00:35:16
    to understanding relative reactivity
  • 00:35:19
    when we start talking about chemical
  • 00:35:20
    reactions later i can't stress
  • 00:35:22
    how important this is for getting a good
  • 00:35:24
    working understanding of how
  • 00:35:26
    the world works from an organic
  • 00:35:28
    chemistry perspective but how chemical
  • 00:35:29
    reactions work
  • 00:35:32
    if you have found this lesson helpful
  • 00:35:34
    consider giving me a like and a share
  • 00:35:35
    that's again the best thing you can do
  • 00:35:36
    to support the channel
  • 00:35:38
    and if you're looking for practice
  • 00:35:39
    problems on asks bases or the study
  • 00:35:41
    guides that go with this
  • 00:35:42
    check out my premium course on
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الوسوم
  • acids and bases
  • organic chemistry
  • REO mnemonic
  • acid-base ranking
  • conjugate base
  • pKa values
  • resonance
  • induction
  • hybridization
  • chemical stability