Q11.73E - Organic Chemistry (Mcmurry)

Question

Propose a structure for an alkyl halide that gives only (E)-3-methyl-2-phenyl-2-pentene on ${\mathbf{E}}_{\mathbf{2}}$ elimination. Make sure you indicate the stereochemistry.

Step-by-Step Solution

Answer

Formation of the desired product

Step 1: Zaitsev’s rule

According to Zaitsev’s rule, base-induced elimination reactions generally give a more stable alkene product—that is, the alkene with more alkyl substituents on the double-bond carbons.

Step 2: Structure of alkyl halide

${\mathrm{E}}_2$-elimination is trans elimination, in which hydrogen and halogen should be in an antiperiplanar position.

The reaction is represented as:

Formation of the desired product