Question
Account for the following:
(i) Formaldehyde gives Cannizzaro’s reaction whereas acetaldehyde does not.
(ii) Carboxylic acids do not give characteristic reactions of carbonyl compounds.
Solution
i) Aldehydes which have an alpha hydrogen atom does not give cannizzaro's reaction. Acetaldehyde, CH3CHO has 3 hydrogens but in case of formaldehyde, HCHO there is no alpha hydrogen present , hence formaldehyde undergoes cannizzaro's reaction where as acetaldehyde does not.
ii) Caroboxylic acids do not give characteristic reaction of carbonyl compounds. This is because the lone pairs on oxygen atoms attached to hydrogen atom in the –COOH group are involved in resonance there by making carbon atom less available.
