Question

The rate of solvolysis of tert-butyl bromide will be maximum in which of the following solvents.
a) $E{t_2}O$
b) $CC{l_4}$
c) $EtOH$
d) ${H_2}O$

Answer 1

Hint: We must know that reaction when the solvent molecule interacts with a substrate molecule is termed as solvolysis. For a solvolysis reaction to occur it is necessary that it has a nucleophilic character and it should support the formation of a polar molecule. The nucleophile will attack the electrophilic center and enhance the reaction.

Complete answer:
We need to know that solvolysis is the reaction where the solvent molecule atoms cause substitution reaction. The solvent should be electron rich and act as a nucleophile. The tert-butyl bromide is a three degree hydrocarbon since 3 methyl groups are attached to the carbon having bromine. The reaction will proceed through unimolecular substitution reaction since the three methyl group will cause steric hindrance and will not enable it to proceed via bimolecular substitution reaction. The carbocation formed via unimolecular reaction is three degree and is stable so it proceeds via unimolecular mechanism only.
Now in the reaction the bromine atom has to be removed and the solvent atom is placed at its position. It is a two step mechanism, the first step is removal of bromine atoms with formation of a tertiary carbocation while the second step is attack by the solvent molecule. A tertiary carbocation is stable due to the hyperconjugation effect.
Hence the best solvent attack is done by water molecule since the oxygen atom present has lone pair of electrons which makes it nucleophilic in nature and hydroxide ion gets attached and alcohol formation occurs. The ${H_2}O$ breaks as ${H^ + }$ and $O{H^ - }$ ions and the $O{H^ - }$ attacks the carbocation and gets attached to the site.
Hence the option (d ) is correct.
The option (a) and (b) are non-polar solvents and thus cannot be used in the reaction. The reaction leads to formation of cation and anion hence a nonpolar molecule will not participate in the reaction. So the options are incorrect (a) and (b) are incorrect.

Hence the option (d ) is correct.

Note:
We need to know that a polar solvent stabilizes the course of unimolecular substitution reaction. The carbocation formed in the reaction will be stabilized by the polar atoms of the solvent present. A nonpolar solvent will not be able to stabilize the carbocation formed during the course of reaction. Hence, it is advised to use polar solvents only.