[Mandeep Deka]

In the HVZ reaction, after the alpha-brominated acyl-bromide is formed it gets hydrolyzed to alpha-brominated carboxylic acid which is the final product. But why doesn't the bromine at the alpha- carbon get substituted by an -OH group? It can undergo nucleophilic substitution for sure!!

[Trave11er]

It probably does both, but substituion at carboxylic carbon is predominant, because 1.) It carries a bigger "+" charge and therefore more readily attracts the nucleophile (electrostatically) 2.) pi-antibonding orbital of carboxylic group C=O bond lies lower in energy than sigma-antibonding C-Br bond, so again substitution at alpha carbon shouldn't be the predominant reaction.