See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The starting material is (cyclohex-1-en-1-yl)acetylene, i.e., 1-(ethynyl)cyclohex-1-ene, which has a terminal alkyne (-C≡CH) attached to a cyclohexene ring at the double-bond carbon. Step 2 - Reaction with NaNH2/NH3 then CH3Br (A): NaNH2 is a strong base that deprotonates the terminal alkyne to form a sodium acetylide (carbanion at the terminal carbon). This acetylide then undergoes SN2 alkylation with CH3Br to give the internal alkyne: (cyclohex-1-en-1-yl)-C≡C-CH3. This is compound (A). Step 3 - Hydrogenation with H2/Lindlar catalyst (B): Lindlar catalyst performs syn-selective partial hydrogenation of the internal alkyne to give a cis (Z) alkene. The triple bond (cyclohex-1-en-1-yl)-C≡C-CH3 is reduced to the cis alkene: (cyclohex-1-en-1-yl)-CH=CH-CH3 with Z (cis) configuration, meaning both H atoms are on the same side of the double bond. Step 4 - Identify product (B): The product is (Z)-(cyclohex-1-en-1-yl)-1-propenyl, i.e., cis-1-(1-propenyl)cyclohex-1-ene. In option (c), the structure shows the cyclohexenyl group attached to C(H)=C(H) with CH3 on the same side as H (cis), consistent with Lindlar hydrogenation giving the Z-alkene. Why other options fail: - Option (a) shows an internal alkyne with no reduction, which would be compound (A), not (B). - Option (b) shows a trans (E) alkene, which would result from dissolving metal reduction (Na/NH3), not Lindlar catalyst. - Option (d) shows a vinyl group (no methyl), which would arise from a different starting material or reaction pathway. Therefore, the correct answer is C.