Question

Predict all the alkenes that would be formed by dehydrohalogenation of the following halides with sodium ethoxide in ethanol and identify the major alkene:
i. 1-Bromo-1-methylcyclohexane
ii. 2-Chloro-2-methylbutane
iii. 3-Bromo-2,2,3-trimethylpentane

Answer 1

i. In 1-Bromo-1-methylcyclohexane, the β-hydrogen atoms on either side of the Br atoms are equivalent, therefore, only one type of product i.e., 1 methylcyclohexene is formed.

ii. 2-Chloro-2-methylbutane has two different sets of equivalent β-hydrogen atoms and hence, in principle can give two alkanes (I and II). But according to Saytzeff’s rule, more highly substituted alkene (II), being more stable, is the major product.

iii. 3-Bromo-2,2,3-trimethylpentane has two different sets of β-hydrogen atoms and hence, in principle, can give two alkenes (I and II). But according to Saytzeff's rule, more highly substituted alkene (II), being more stable, is the major product.