(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.

(a) Explain the mechanism of a nucleophilic attack on the carbonyl gro

1.	(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» Solution :(a) Mechanism of nucleophilic addition reactions : attack from the top face ` (##SB_CHM_XII_DB_2010_E01_034_S01.png" width="80%"> 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 as shown in Fig. (b) Q.30 (or) (b) Outside Delhi, Set-I., 2009. .