Question

The isobutyl cation spontaneously rearranges to the tert-butyl cation by a hydride shift. Is the rearrangement exergonic or endergonic? Draw what you think the transition state for the hydride shift might look like according to the Hammond postulate.

Short answer

The structure of hydrocarbon formed from alkyl bromide is,

Step-by-step solution

Hammond's postulate

According to the Hammond postulate, for exothermic reactions, the transition state structure resembles reactants than products, and the reaction reaches early.For endothermic reactions, the situation is different.

The transition state for the hydride shift

When there is a rearrangement of isobutyl cation to tert-butyl cation by a hydride shift, the rearrangement is exergonic because it is spontaneous.

According to the Hammond postulate, isobutyl cation's transition state resembles isobutyl cation.

The transition state for the hydride shift