Explain why the main product of the electrophilic addition of hydrogen bromide to propene is 2-bromopropane and not 1-bromopropane. Include reaction mechanisms and stability of intermediate carbocations in your answer.
Answers
Answer:
Explanation:
[Throughout the question, references will be made to a diagram which shows the mechanism of the reaction] In organic addition reactions like the one described in the question, an unstable intermediate carbocation forms after the electrophilic attack from the partially positive hydrogen on the hydrogen bromide. The alkyl groups in that carbocation are able to it a bit (so that it stays in that state until the bromide can make its nucleophilic attack) due to their positive induction effects: the alkyl groups push electron density towards the positive charge and away from themselves to lessen the density of that positive charge. When forming 1-bromopropane, the primary carbocation is by only one such positive induction effect. However, when forming 2-bromopropane, the secondary carbocation is by two positive induction effects, making it a more stable carbocation. Thus, the secondary carbocations are more likely to last longer for the bromide to complete its nucleophilic attack, leading to 2-bromopropane being the main product of the reaction.