Which of the following compounds will give racemic mixture on nucleophilic substitution by `OH^(-)` ion?
(I) `CH_(3)-underset(C_(2)H_(5))underset(|)(C)H-Br`
(II) `CH_(3)-underset(C_(2)H_(5))underset(|)overset(Br)overset(|)(C)-CH_(3)`
(III) `CH_(3)-underset(C_(2)H_(5))underset(|)(C)H-CH_(2)Br`

Options

A. (i)
B. (i), (ii) and (iii)
C. (ii) and (iii)
D. (i) and (iii)

Answer

A

Explanation

A mixture containing two enantiomers in equalimolar amount have zero optical rotation, as the rotation due to one isomer is cancelled by the rotation due to other isomer. Such a mixture is known as racemic mixture. All those compounds which follow `S_N^2` mechanism during nucleophilic substitution reaction form racemic mixture Order of reactivity of alkyl halides towards `S_N^1` and reactions as follows:
Tertiary halide, secondary halide, primary halide, `CH_3X`
For `S_N^1` reaction
Thus, `CH_3-underset(C_2H_5)underset(|)overset(*)(CH)-Br` contains a chiral carbon and gives a racemic product.