Question

How many distinct alkenes obtained from the 3-Bromo-3-methylhexane upon treatment with alc. KOH?

• A. 2
• B. 3
• C. 4
• D. 5

Hint:

When predicting the products of elimination reactions, always consider all possible $\beta$-hydrogens that can be removed, leading to different alkene isomers. Also, carefully examine the structure of each resulting alkene to determine if it can exhibit geometric isomerism (cis/trans isomers), which will count as distinct products.

Answer 1

The Correct Option is C

Step 1: Identify the $\beta$-hydrogens and possible alkenes.
Dehydrohalogenation can occur at C2 and C4.
Elimination at C2 gives 3-methylhex-2-ene: $CH_3-CH=C(CH_3)-CH_2-CH_2-CH_3$ (can exist as cis and trans isomers).
Elimination at C4 gives 3-methylhex-3-ene: $CH_3-CH_2-C(CH_3)=CH-CH_2-CH_3$ (can exist as cis and trans isomers).
Step 2: Count the distinct alkenes including stereoisomers.
1. cis-3-methylhex-2-ene
2. trans-3-methylhex-2-ene
3. cis-3-methylhex-3-ene
4. trans-3-methylhex-3-ene
There are 4 distinct alkenes. Thus, the number of distinct alkenes is $ \boxed{4} $.