Question

Predict the order of reactivity of these alkyl halides: 2-bromobutane, 2-bromo-2-methylpropane, 1-bromobutane, bromocyclohexane, α-bromotoluene, bromobenzene, 1-bromoadamantane; in NaI/acetone, specify what type of mechanism they will undergo and Explain in detail how you arrived at your conclusion.

Answer 1

It follows SN₂ reaction mechanism and the ability of the leaving group decides the rate of the reaction. The faster the leaving group leaves the faster will be the reaction go. As the nucleophile attacks from the opposite side of the Leaving group the bulkier groups are easy to leave the molecule.

The SN₂ mechanism is a 1 step reaction. i.e the bond formation between the Nucleophile and the molecule and the bond breaking between the leaving group and the molecule happens at the same time.

Hence due to steric and electrostatic repulsion, the reactivity order for this mechanism follows

Primary carbon> Secondary >Tertiary.

As there is a huge steric hindrance and repulsion in molecules where the functional group is attached to a tertiary carbon it's really difficult to attack from behind and form products.