question_answer

In a nucleophilic substitution reaction: \[R-Br+C{{l}^{-}}\xrightarrow[{}]{DMF}R-Cl+B{{r}^{-}},\]which one of the following undergoes complete inversion of configuration?   [JEE Main Online Paper ( Held On 09 Apirl  2014  )

A) \[{{C}_{6}}{{H}_{5}}CH{{C}_{6}}{{H}_{5}}Br\]      

B) \[{{C}_{6}}{{H}_{5}}C{{H}_{2}}Br\]

C) \[{{C}_{6}}{{H}_{5}}CHC{{H}_{3}}Br\]

D) \[{{C}_{6}}{{H}_{5}}CC{{H}_{3}}{{C}_{6}}{{H}_{5}}Br\]

Correct Answer: C

Solution :

                \[{{C}_{6}}{{H}_{5}}CHC{{H}_{3}}Br\] being an optically active secondary alkyl bromide undergoes \[{{S}_{N}}2\] nucleophilic substitution reaction. Hence it undergoes complete inversion of configuration.