Question

Balanced equation and complete mechanism:

1:1 methanol:water + 0.5M NaOH + 2-bromo-2-methylpropane

1:1 ethanol:water + 0.5M NaOH + 2-bromo-2-methylpropane

1:1 propanol:water + 0.5M NaOH + 2-bromo-2-methylpropane

1:1 acetone:water + 0.5M NaOH + 2-bromo-2-methylpropane

Answer 1

2-bromo-2-methylpropane is a tertiary alkyl halide. On treating with 0.5 M NaOH it undergo SN1 reaction to form a tertiary buty alcohol.

The rate of SN1 reaction depends on the polarity of solvent, and as polarity of solvent increases the rate of SN1 reaction also increases.

The polarity of given solvent combinations are in the decreasing order of

1:1 methanol:water>1:1 ethanol:water>1:1 propanol:water>1:1 acetone:water

Therefore the rate of reaction between 2-bromo-2-methylpropane and NaOH also varies in same order as above.

Mechanism of SN1 involves two steps:

A) Ionization of alkylhalide to form carbocation.

(CH3)3C-Br -------> (CH3)3C^+ + Br-

Its is slow step and rate determining step and the rate of the bond breaking is directly proportional to the solvent polarity.

B) Attack of nucleophile on carbocation to form product.

(CH3)3^+ +NaOH ----> (CH3)3C-OH + NaBr

It is fast step.