Question

Write the product when trans-1-bromo-2-methylcyclohexane gets through dehydrohalogenation with sodium metoxide in ethanol.

Answer 1

In trans-1-bromo-2-methylcyclohexane, Br at equatorial position is more stable conformation. Thus E2 elimination can not occur from this more stable conformation. Ring flip gives less stable conformation in which bromine becomes axial & also antiperiplaner to H at C6. So, E2 elimination generates double bond only between C1 & C6.

So, sodium methoxide in ethanol solvent act as base and abstact H from C6 axial position. It gives 3-methylcyclohexene as 100% product. While 1-methylcyclohexene is not formed.