Question

The IUPAC name of following compound is

• A. 2-Chloro-3-methylpent-3-ene
• B. 4-Chloro-3-methylpent-2-ene
• C. 1-Chloro-1,2-dimethylbut-2-ene
• D. 4-Chloro-3,4-dimethylbut-2-ene

Hint:

Always remember the priority order: Principal Functional Group $>$ Double/Triple Bonds $>$ Halogens/Alkyl groups. Even though numbering from the right gives the chlorine substituent a lower number (2 instead of 4), the double bond dictates the numbering sequence because it holds a higher priority!

Answer 1

The Correct Option is B

Step 1: Read the structure.
The molecule is $\text{CH}_3\text{-CH=C(CH}_3)\text{-CH(Cl)-CH}_3$, a five-carbon chain carrying a double bond, a methyl branch and a chlorine.
Step 2: Pick the parent chain.
The longest chain that includes the C=C runs through all five carbons, so the parent is pentene.
Step 3: Choose the numbering direction.
The double bond must get the lowest locant. Numbering left to right places the double bond at C2; right to left would place it at C3, so we number left to right.
Step 4: Locate the substituents.
With left-to-right numbering, the methyl sits on C3 and the chlorine on C4.
Step 5: Confirm the double-bond locant.
The double bond spans C2-C3, so it is named pent-2-ene.
Step 6: Order substituents alphabetically.
Chloro comes before methyl, giving 4-chloro-3-methyl.
Step 7: Write the full name.
Combining gives 4-Chloro-3-methylpent-2-ene, which is option (2).
\[ \boxed{\text{4-Chloro-3-methylpent-2-ene}} \]