Question

(a) Explain the mechanism of a nucleophilic attack on the carbonyl group of an aldehyde or a ketone.
(b) An organic commpound (A) (molecular formula `C_(8)H_(16)O_(2)`) was hydrlysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidatin of (C) with chromic acid also produced (B). On dehydratin (C) gives but-1-ene. Write the equations for the reactions involved.

Answer 1

(a) Mechanism of nucleophilic addition reactions :
attack from the top face
A nucleaphile attacks the electrophilic carbon atom of the polar carbonyl group from a direction perpendicular to the plane of `sp^(2)` hybridised orbitals of carbonyl carbon. The hybridisation of carbon changes from `Sp^(2) to sp^(3)` in this process and a tetrahedral alkoxide intermediate is produced.
This intermediate captures a proton from the reaction medium to give the electrically neutral product. The net result is additon of `Nu^(-)and H^(+)`across the carbon oxygen double bond.