1. Identify the substrate and the reaction type

We have 3-bromo-3-cyclopentylhexane undergoing dehydrobromination with alcoholic KOH, so the reaction is an elimination (E2).

The carbon bearing bromine is carbon-3 of hexane:

$\text{CH}_3-\text{CH}_2-\text{C}(\text{Br})(\text{cyclopentyl})-\text{CH}_2-\text{CH}_2-\text{CH}_3$

Call the carbon bearing Br the $\alpha$-carbon. Elimination can occur by removing a $\beta$-hydrogen from any carbon directly attached to this $\alpha$-carbon.

2. Find all $\beta$-carbons

The $\alpha$-carbon is attached to three carbons:

• carbon-2 of the hexane chain
• carbon-4 of the hexane chain
• the carbon of the cyclopentyl ring attached to it

So there are 3 possible $\beta$-positions.

Thus, three different constitutional alkene frameworks are possible:

(i) Elimination from carbon-2

This gives a double bond between C2 and C3:

$\text{hex-2-ene type alkene with cyclopentyl at C3}$

Structure:

$\text{CH}_3-\text{CH}=\text{C}(\text{cyclopentyl})-\text{CH}_2-\text{CH}_2-\text{CH}_3$

This alkene shows geometrical isomerism (E/Z) because each double-bond carbon has two different substituents:

• at C2: $\text{H}$ and $\text{CH}_3$
• at C3: cyclopentyl and propyl

So this gives:

• one $E$ isomer
• one $Z$ isomer

Total from this path = 2 alkenes.

(ii) Elimination from carbon-4

This gives a double bond between C3 and C4:

Structure:

$\text{CH}_3-\text{CH}_2-\text{C}(\text{cyclopentyl})=\text{CH}-\text{CH}_2-\text{CH}_3$

Again, geometrical isomerism is possible:

• at C3: cyclopentyl and ethyl
• at C4: H and ethyl

So this also gives:

• one $E$ isomer
• one $Z$ isomer

Total from this path = 2 alkenes.

(iii) Elimination from the cyclopentyl ring carbon attached to the $\alpha$-carbon

This forms an exocyclic double bond between the side-chain carbon and the ring carbon.

This gives a methylene/exocyclic-type alkene on the ring junction carbon.

Here, no geometrical isomerism is possible because on the ring carbon, the two paths around the unsubstituted cyclopentane ring are identical.

So this gives only 1 alkene.

3. Total number of alkenes

Therefore,

$2 + 2 + 1 = 5$

4. Comparison with stored answer

Derived answer = 5

Stored correct answer = 5

So they agree.