In a nucleophilic substitution reaction: R-Br + Cl- xrightarrowDMF R-Cl + Br- , which one of the following undergoes complete inversion of configuration ?

Question

In a nucleophilic substitution reaction: R-Br + Cl- xrightarrowDMF R-Cl + Br- , which one of the following undergoes complete inversion of configuration ? (A) C6H5CHC6H5Br (B) C6H5CH2Br (C) C6H5CH CH3Br (D) C6H5CCH3C6H5Br

Tardigrade Admin · Accepted Answer

In the compound of option B, bromine is attached to a primary carbon atom.
The substitution occurs via

S N_{2}

mechanism which involves the inversion of configuration.
In the remaining compounds the bromine is attached to a secondary or tertiary carbon atom. In case of secondary carbon atom (options A and C), the
substitution occurs via a combination of

S N_{1}

and

S N_{2}

mechanisms. Hence, complete inversion of configuration is not possible.

In case of tertiary carbon atom, (option D) the substitution occurs via

S N_{1}

mechanism which cannot result in complete inversion of configuration.

Q. In a nucleophilic substitution reaction :
$R - B r + C l^{-} D MF R - Cl + B r^{-},$
which one of the following undergoes complete inversion of configuration ?

$C_{6} H_{5} C H C_{6} H_{5} B r$

$C_{6} H_{5} C H_{2} B r$

$C_{6} H_{5} C H C H_{3} B r$

$C_{6} H_{5} CC H_{3} C_{6} H_{5} B r$

Q. In a nucleophilic substitution reaction : R−Br+Cl−DMF​R−Cl+Br−, which one of the following undergoes complete inversion of configuration ?

C6​H5​CHC6​H5​Br

C6​H5​CH2​Br

C6​H5​CHCH3​Br

C6​H5​CCH3​C6​H5​Br

Q. In a nucleophilic substitution reaction :
$R - B r + C l^{-} D MF R - Cl + B r^{-},$
which one of the following undergoes complete inversion of configuration ?

$C_{6} H_{5} C H C_{6} H_{5} B r$

$C_{6} H_{5} C H_{2} B r$

$C_{6} H_{5} C H C H_{3} B r$

$C_{6} H_{5} CC H_{3} C_{6} H_{5} B r$