See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Catalytic hydrogenation (H2/Pt) adds H2 across a C=C double bond to give the corresponding alkane. To find all alkenes that yield 2-methylbutane (isopentane, CH3CH(CH3)CH2CH3) upon hydrogenation, we must identify every possible position where a double bond can exist in the 2-methylbutane carbon skeleton. 2-Methylbutane has the skeleton: C1-C2(CH3)-C3-C4, i.e., (CH3)2CHCH2CH3. Step 1: Identify all possible double bond positions in this skeleton. The carbon skeleton of 2-methylbutane is: C1: CH3 C2: CH (branching point, also attached to C1-methyl) C3: CH2 C4: CH3 and a methyl branch on C2. Possible double bonds (considering all unique alkene constitutional isomers and geometric isomers): 1) 2-Methyl-1-butene: CH2=C(CH3)CH2CH3 — double bond between C1 and C2. 2) 2-Methyl-2-butene: CH3C(CH3)=CHCH3 — double bond between C2 and C3. This alkene has cis/trans... actually 2-methyl-2-butene is (CH3)2C=CHCH3, which has no geometric isomers (one side has two methyls). 3) 3-Methyl-1-butene: CH2=CHCH(CH3)2 — double bond between C1 and C2 of the straight chain (i.e., between what becomes C3 and C4 in a renumbered sense). Wait, let me re-examine. The carbon skeleton of 2-methylbutane: (CH3)2CH-CH2-CH3 Label: Ca-Cb-Cc-Cd with a methyl on Cb. Actually: C1(CH3), C2(with methyl branch), C3, C4. All positions for double bonds: - Between C1 and C2: gives 2-methyl-1-butene: CH2=C(CH3)-CH2-CH3 - Between C2 and C3: gives 2-methyl-2-butene: (CH3)2C=CH-CH3 - Between C3 and C4: gives 2-methyl-3-... wait, that would be (CH3)2CH-CH=CH2, which is 3-methyl-1-butene. - Between C2 and the branch methyl (C2 and Cmethyl): gives 2-methylenbutane... that is CH2=C(CH2CH3)(CH3)... no. Actually placing a double bond between C2 and the methyl branch carbon gives: CH3-C(=CH2)-CH2-CH3, which is 2-methyl-1-butene... no, that is the same as option 1 just written differently. Actually this IS 2-methyl-1-butene (the exo-methylene). Yes, same compound. So the three distinct alkenes are: 1. 2-Methyl-1-butene: CH2=C(CH3)CH2CH3 2. 2-Methyl-2-butene: (CH3)2C=CHCH3 3. 3-Methyl-1-butene: (CH3)2CHCH=CH2 All three have the correct carbon skeleton and upon H2/Pt hydrogenation give 2-methylbutane. Step 2: Check for geometric isomers — 2-methyl-2-butene has no cis/trans isomerism (C2 bears two methyls), and 2-methyl-1-butene and 3-methyl-1-butene are terminal alkenes with no geometric isomers. So total = 3 alkenes. Why other options fail: - (a) 1 and (b) 2 undercount the number of possible double bond positions. - (d) 4 would require a geometric isomer pair among these, which does not exist here. Therefore, the correct answer is C.