Question

The reaction of tertiary butyl chloride in water to yield tertiary butyl alcohol is not appreciably affected by dissolved $NaF$. In DMSO, however, $NaF$ bring about rapid formation of isobutene. It is because of

• A. In DMSO, reaction predominates over $S_{N}1$
• B. E2 reaction is preferred over $S_{N}1$ in DMSO
• C. E2 reaction is preferred over $S_{N}2$ in DMSO
• D. Fluoride ion is solvated by DMSO

Answer 1

The correct option is B

E2 reaction is preferred over $S_{N}1$ in DMSO

Tertiary butyl alcohol in water yield tertiary butyl alcohol by $S_{N}1$ reaction. When $NaF$ is added to this, the $F^{-}$ ions are solvated by the polar protic solvent $\left(H_{2}O\right)$. Thus, $F^{-}$ becomes a weak base to undergo elimination reaction.

But when $NaF$ is added to polar aprotic solvent (DMSO) with tertiary butyl choride, $F^{-}$ is strong enough to abstract the proton and gives a elimination product by E2 mechanism.
$F^{-}$ is not solvated by DMSO solvent.

Hence, (b) is correct.