Question

Do both elimination reactions, E1 and E2, follow Zaitsev’s rule?

Answer 1

`"E1"` eliminations follow Zaitsev's rule. With two exceptions, `"E2"` reactions also follow Zaitsev's Rule.

Explanation:

(1) Certain cyclohexane derivatives.

Some cyclohexane derivatives, such as menthyl chloride, form the Hofmann product instead:

(from en.wikipedia.org)

Formation of the Zaitsev product requires antiperiplanar elimination at the 2-position, but the isopropyl group – not the proton – is in the antiperiplanar location.

(from en.wikipedia.org)

But there is an antiperiplanar hydrogen at the 6-position, so elimination occurs there and produces only the Hofmann product.

(2) Bulky bases

(from www.masterorganicchemistry.com)

A bulky base attacks the least sterically hindered proton to form the Hofmann product.