Question

Predict the products of E1 elimination of the following compounds. Label the major products.

Answer 1

The E1 is called unimolecular elimination reaction because the rate-limiting transition state involves a single molecular rather than a collision between two molecules. In the first step (it is a slow step), the substrate ionizes into carbocation. In the second step, base abstracts proton from adjacent to the carbocation to form two different alkenes. Here, more substituted alkene is a major product and less substituted alkene is a minor product.

(a) The substrate can be ionized into carbocation and bromide ion.

Base abstracts proton from adjacent to the carbocation to form more substituted alkene. It is a major product.

Base abstracts proton from adjacent to the carbocation to form less substituted alkene. It is a minor product.

(b) The substrate can be ionized into carbocation and bromide ion.

Here, the secondary carbocation can be rearranged to form more stable tertiary carbocation.

Base abstracts proton from adjacent to the carbocation to form less substituted alkene. It is a minor product.

Base abstracts proton from adjacent to the carbocation to form more substituted alkene. It is a major product.

(c) The substrate can be ionized into carbocation and bromide ion.

Here, the secondary carbocation can be rearranged to form more stable tertiary carbocation.

Base abstracts proton from adjacent to the carbocation to form less substituted alkene. It is a minor product.

Base abstracts proton from adjacent to the carbocation to form more substituted alkene. It is a major product.