Question

27 multiple choice 2 points which of the following additions to alkenes occur(s) specifically in an anti fashion? addition of br₂ addition of h₂ hydroboration - oxidation addition of h₂o in dilute acid

Explanation:

Step1: Addition mechanism of \(Br_2\)

Alkenes react with \(Br_2\) via a bromonium ion intermediate. The bromide ion attacks from the opposite side of the bromonium ion, leading to anti - addition.

Step2: Addition mechanism of \(H_2\)

Hydrogenation (\(H_2\) addition) occurs via a syn - addition mechanism as hydrogen atoms add to the same face of the alkene (on a metal catalyst surface).

Step3: Hydroboration - oxidation mechanism

Hydroboration - oxidation has a syn - addition of \(BH_3\) (and subsequent oxidation gives an overall syn - addition of \(H\) and \(OH\) across the double bond).

Step4: Addition of \(H_2O\) in dilute acid mechanism

The addition of \(H_2O\) in dilute acid (acid - catalyzed hydration) has a carbocation intermediate. There is no strict anti - addition preference; it can have some rearrangements and non - specific addition patterns compared to the well - defined anti - addition of \(Br_2\).

Answer:

addition of \(Br_2\)