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Q. What is the major product alkene formed in the following elimination?

Question

NTA AbhyasNTA Abhyas 2020Haloalkanes and Haloarenes

Solution:

Oxidation of a tertiary amine with a peroxide (mCPBA) forms an N-oxide that undergoes an intramolecular deprotonation with syn-stereoselectivity upon heating. This reaction is known as a Cope elimination. This deprotonation will occur on a less hindered beta-carbon, giving rise to a less substituted alkene product (this regioselectivity, known as the Hofmann's rule, is the opposite predicted by Zaitsev's rule).

Hofmann's β-elimination by abstraction of β H-atom from C which is least substituted.

Solution