Question

(a) Write the resonance structure of `RCOOH`.
(b) Why is `(C-O)` bond shorter in `RCOOH` than in `ROH`
( c) Compare the `(C=O)` bond length in `RCOOH` and `RCHO`.
(d) Compare the reactivities of `(C=O)` in `RCOOH` and `RCHO` towards nucleophilic addition `(N.A.)` reactions.

Answer 1

(a)
(b) In the resonance charge-separated structure `(II)`, there is some double-bond character in the `(C-O)` bond of the acid, which shortens its bond length. So the length of `(C-O)` in acid is shorter than that in `ROH`.
( c) In the resonance structure `(II)`, there is some single-bond character in `(C=O)` bond of the acid, which makes it longer than that in `RCHO`. So the bond length of `(C=O)` in acid is longer than in `RCHO` or ketones.
(d) In `RCOOH`, there is less positive charge in the `(C=O)C` atom which makes this `C` atom less eletrophilic and less reactive towards nucleophiles. So `RCOOH` is less reactive than aldehydes and ketones towards nucleophilic addition `(N.A.)` reactions.