2-methylprop-1-ene is an isomer of?

Step 1: Analyze the question We need the compound that is an isomer of 2-methylprop-1-ene. Isomers have the same molecular formula but different structures.

Step 2: Find the molecular formula of 2-methylprop-1-ene

• Parent chain: prop-1-ene (3 carbons, C=C at position 1)
• A methyl group is on carbon 2
• Structure: CH₂=C(CH₃)–CH₃
• Total carbons = 4, so the formula is C₄H₈ (alkene, CₙH₂ₙ)

Step 3: Find the formula of each option

• A. 3-methylbut-1-ene: 4 + 1 = 5 carbons → C₅H₁₀
• B. 2-methylbut-1-ene: 4 + 1 = 5 carbons → C₅H₁₀
• C. but-2-ene: 4 carbons → C₄H₈
• D. pent-2-ene: 5 carbons → C₅H₁₀

Step 3 result: Only but-2-ene has the formula C₄H₈.

Step 4: Confirm they are structural isomers

• 2-methylprop-1-ene: CH₂=C(CH₃)₂ (branched chain)
• but-2-ene: CH₃–CH=CH–CH₃ (straight chain)

Same formula, different arrangement of atoms, so they are structural (chain) isomers.

Answer: C. but-2-ene

Tip: For "isomer of" questions, count the carbons first. Add the parent chain carbons and the branch carbons, then compare the formulas. Any option with a different carbon count can be eliminated immediately. Note that 2-methylprop-1-ene has three C₄H₈ isomers: but-1-ene, but-2-ene, and itself (plus cyclic ones like cyclobutane).