I have an acid and base organic chem quiz tomorrow and I need help determining how acidic protons are. I understand the concept of atoms, resonance, induction, and orbital when considering the acidity of protons. However, when I'm given these molecules, it overwhelms me so I don't understand how to break them down. I believe that the first step is that I have to find the conjugate base for each one and then just compare? Below is photo of my worksheet. I have already filled in the correct answers. Thanks in advance for your help.

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    $\begingroup$ Authors managed to ignore amide H atom... $\endgroup$
    – Mithoron
    Sep 14, 2016 at 10:26
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    $\begingroup$ @Mithoron I think it's quite common (and deliberate) to ignore the amide hydrogen. I would guess that the overall topic is CH-acidity here. $\endgroup$ Sep 14, 2016 at 11:15
  • $\begingroup$ Maybe you could try answering by the inductive effect on the carbon containing the acidic hydrogen. The electron cloud of the carbon c is more depleted than d which is more depleted than b which is more depleted than a. However, I am not sure. $\endgroup$ Sep 14, 2016 at 12:33
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    $\begingroup$ @Jan if I were the author, and I actually have asked these questions quite often, I would not do it any other way. The hetero atom is too obvious to count. If I were having a test about CH acidity, I would deduce points for giving that answer. You don't know the intend of the question, so you should not judge if it is better or who worse. $\endgroup$ Sep 14, 2016 at 16:46
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    $\begingroup$ There's instructional value in including this heteroatom imo. Not saying it's better or worse but it's also useful to know an approximate pKa for amide NH and amine NH compared to the various CH protons there (the 1,3-dicarbonyl and the carbonyl). In any case the question does strongly imply that only the labelled hydrogens are to be labelled, so there is no fault in the question. $\endgroup$ Sep 14, 2016 at 17:50

1 Answer 1


the c hydrogen is more acidic because it is stacked between two electron withdrawing carbonly groups, and after the loss of hydrogen the carbanion is more stabilized, where as the same thing is not observed in case of d hydrogen the carbanion is in conjugation but only with one of carbonly group followed by b and c hydrogen.

now in case of second example, e is more acidic because it is allylic as well as next to the carbonyl group which means the anion after loss of hydrogen is more stabilized as come to f and g.


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