Hofmann Elimination

When an alkyl halide with a charged nitrogen group (alkylammonium ion) undergoes an elimination reaction, the less-substituted alkene is usually the major product. This is different from the usual trend, where the more substituted alkene is favored (Zaitsev’s rule).

This type of elimination is called the Hofmann elimination, and the less-substituted alkene is called the Hofmann product.

Why is the Hofmann Product Favored?

The reason for this preference is due to steric hindrance. The bulky nitrogen group (NR₃) creates steric interactions with neighboring alkyl groups during the elimination reaction. These interactions are less severe when the less-substituted alkene is formed, making it the favored product.

Example:

In this example, the Hofmann product (the less-substituted alkene) is the major product due to the steric interactions involving the NR₃ group.