Which compound in each of the following pairs will react faster in SN2 reaction with –OH?
(i) CH3Br or CH3I (ii) (CH3)3CCl or CH3Cl
(i) Since I- ion is a better leaving group than Br- ion, therefore, CH3I reacts faster CH3Br in SN2 reaction with OH- ion.
Note: Better the leaving group, faster is the SN2 reaction.
(ii) On steric grounds, 1◦ alkyl halides are more reactive than tert-alkyl halides in SN2 reactions. Therefore, CH3Cl will react at a faster rate than (CH3)3CCl in a SN2 reaction with OH- ion.(bulkier the g8roup, slower is the SN2 reaction.)