Chapter 10, Problem 10.64P

Interpretation Introduction

Interpretation:

The complete mechanism that leads to the three alkenes produced by $\text{N-ethylhexan-3-amine}$ under Hofmann elimination conditions is to be drawn, and the major product is to be predicted.

Concept introduction:

Hofmann elimination is an E2 elimination of an amine group along with a $\text{β}$ hydrogen to produce an alkene. Unlike most elimination reactions that preferentially form the most substituted alkenes, Hofmann elimination preferentially forms the least substituted alkene.

When two different types of $\text{β}$ hydrogens are present, the one from the less substituted carbon is removed preferentially. The leaving group in Hofmann elimination is a bulky tertiary amine group ${\text{NR}}_{\text{3}}$. An E2 reaction is a single-step concerted reaction. It requires that the two groups that are eliminated must be anti to each other. The most stable conformer has the $\text{β}$ hydrogen in anti position on the less substituted carbon. This gives a least substituted alkene as the major product.