Question

(a) Although phenoxide ion has more number of resonating structures than Carboxylate ion, Carboxybc acid is a stronger acid than phenol. Give two reasons.
(b) How will you bring about the following conversions?
(1) Propanone to propane
(ii) Benzoyl chloride to benzaldehyde
(iii) Ethanal to but-2-enal

Answer 1

(a) On losing a proton carboxylic acids forms carboxylate ion and phenol forms phenoxide ion as follows :

Now, the negative change is delocalized in both molecules as follows :

The conjugte base of carboxylic acid has two resonance structures in which negative charge in delocalized over two oxygen atoms which stabilizes the carboxylate ion.
On the other hand, in phenoxide ion the charge is delocalized over entire molecule on the less electronegative atom, thus resonance of phenoxide is not important in comparison to resonance in carboxylate ion.
Thus, Phenol is less acidic then carboxylic acids. In other words, carboxylic acids stronger acid than phenol.
(b) (i) `CH_3-underset("Propanone")underset(O)underset(||)C-CH_3underset(Zn(Hg)+HCl)overset("Clemmens on reduction")toCH_3-underset("Propane")(CH_2)-CH_3`