For the molecule below, is the hydrogen with the oxygen more acidic or is it the one with sulfur?

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Since both parts have the same number of resonance structures, I'm guessing it just boils down to whether or not an atom's electronegativity or size takes precedence in determining whether the proton is more acidic.

So, is size or electronegativity more important in acidity?

Thanks in advance!


1 Answer 1


The size is more significant and the thiocarboxylic acid would be more acidic.

Whilst electro negativity facilitates the stabilisation of a negative charge, the larger size of the sulfur both:

  • Makes the S-H bond weaker than the O-H bond.
  • Helps to stabilise the negative charge on the sulfur.

Hence sulfur derivatives are usually more acidic than their oxygen counterparts. H2S more acidic than H2O and thiols more acidic than alcohols, etc.

  • 2
    $\begingroup$ I think you mean the dithiocarboxylic acid $\endgroup$
    – Waylander
    Commented Sep 28, 2023 at 17:19
  • $\begingroup$ Yes sorry thanks for the correction $\endgroup$
    – Kirandk
    Commented Sep 28, 2023 at 17:22
  • $\begingroup$ Ic that makes sense. thanks :) $\endgroup$
    – Max0815
    Commented Sep 28, 2023 at 17:29

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