Question

Identify the chain isomers from the following

• A. Pent-1-ene and Pent-2-ene
• B. 2-Methylbut-1-ene and 2-Methylbut-2-ene
• C. Pent-2-ene and 2-Methylbut-2-ene
• D. 2-Methylbut-1-ene and 3-Methylbut-1-ene

Hint:

Chain isomers differ in carbon skeleton, not double bond position. Draw structures to compare branching. Ensure same molecular formula. Distinguish from position or functional isomers.

Answer 1

The Correct Option is D

1. Chain isomers have the same molecular formula but different carbon skeletons. All options are C$_5$H$_{10}$.
2. (1) Pent-1-ene (CH$_2$=CH-CH$_2$-CH$_2$-CH$_3$) and Pent-2-ene (CH$_3$-CH=CH-CH$_2$-CH$_3$): Same chain, position isomers.
3. (2) 2-Methylbut-1-ene ((CH$_3$)$_2$C=CH$_2$) and 2-Methylbut-2-ene (CH$_3$-C(CH$_3$)=CH-CH$_3$): Same branched chain, position isomers.
4. (3) Pent-2-ene and 2-Methylbut-2-ene: Different skeletons (straight vs branched), but not chain isomers in strict sense.
5. (4) 2-Methylbut-1-ene and 3-Methylbut-1-ene (CH$_2$=C(CH$_3$)-CH$_2$-CH$_3$ vs CH$_2$=CH-CH(CH$_3$)$_2$): Different branching, chain isomers.
6. Thus, the answer is (4).