Predict the major product 'Z' in the following sequence of...

The given reactant is 2-phenylpropene, $C_6H_5-C(CH_3)=CH_2$.

Reaction with $HBr$ in the presence of benzoyl peroxide proceeds via a free radical mechanism, resulting in anti-Markovnikov addition. The bromine radical adds to the less substituted carbon to form a stable benzylic radical intermediate, which then abstracts a hydrogen atom from $HBr$.

$C_6H_5-C(CH_3)=CH_2 \xrightarrow{\text{HBr, peroxide}} C_6H_5-CH(CH_3)-CH_2Br$

The product 1-bromo-2-phenylpropane undergoes a nucleophilic substitution reaction with $KCN$ in ethanol. The cyanide ion displaces the bromide ion.

$C_6H_5-CH(CH_3)-CH_2Br \xrightarrow{\text{KCN, EtOH, } \Delta} C_6H_5-CH(CH_3)-CH_2CN$

Acidic hydrolysis of the nitrile group ($-CN$) converts it into a carboxylic acid group ($-COOH$).

$C_6H_5-CH(CH_3)-CH_2CN \xrightarrow{H_3O^+, \Delta} C_6H_5-CH(CH_3)-CH_2COOH$

The final product 'Z' is $C_6H_5-CH(CH_3)-CH_2COOH$. Numbering the principal carbon chain starting from the carboxyl carbon gives 3-phenylbutanoic acid.

Answer: 3-Phenylbutanoic acid