Question

Identify the major product in the following reaction.

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

Answer 2

This is an elimination reaction (E2 mechanism) where the hydroxide ion acts as a strong base. The steps of the reaction are as follows:
Step 1: Identify the base and leaving group
In the presence of $\text{OH}^-$ and EtOH, the bromine atom ($\text{Br}$) acts as the leaving group. The hydroxide ion abstracts a proton ($\text{H}^+$) from the adjacent carbon atom, resulting in the formation of a double bond.
Step 2: Formation of the double bond
Since the reaction proceeds via the E2 mechanism, the elimination occurs in a single step. The base removes a $\beta$-hydrogen atom (attached to the carbon next to the carbon with $\text{Br}$), and the $\text{Br}^-$ leaves, resulting in the formation of a double bond between the $\alpha$- and $\beta$-carbons.
Step 3: Determine the major product
The double bond forms between the $\alpha$-carbon (the one originally bonded to the bromine atom) and the $\beta$-carbon. Due to Zaitsev's rule, the most substituted alkene is the major product. Hence, the major product is cyclopentene with a methyl ($\text{CH}_3$) substituent.
Final Answer: (3) Cyclopentene with a $\text{CH}_3$ substituent.