See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 – Formation of compound (A): Phenylacetylene (Ph–C≡C–H) is treated with NaNH2 (a strong base) to deprotonate the terminal alkyne, generating the acetylide anion Ph–C≡C⁻. This nucleophile then undergoes SN2 alkylation with cyclohexyl tosylate (TsO–cyclohexyl) to give Ph–C≡C–Cy, i.e., phenyl cyclohexyl acetylene (internal alkyne). Compound A = Ph–C≡C–Cy. Step 2 – Formation of compound (B): The internal alkyne Ph–C≡C–Cy is subjected to dissolving metal reduction conditions (Na/NH3 liquid). This is a Birch-type reduction of an alkyne, which gives the trans (E)-alkene via anti addition of two hydrogen atoms. Product B = trans-PhCH=CHCy (E-1-phenyl-2-cyclohexylethylene), a trans-disubstituted alkene with Ph and Cy on opposite sides. Step 3 – Formation of compound (C): The trans-alkene B is treated with MCPBA (meta-chloroperoxybenzoic acid), a standard peracid epoxidation reagent. Peracid epoxidation of alkenes proceeds with syn addition of the oxygen across the double bond, retaining the relative stereochemistry of the alkene. Since B is trans (Ph and Cy on opposite faces of the double bond), the resulting epoxide will have Ph and Cy on opposite faces (trans relationship in the epoxide ring). This corresponds to the trans-epoxide shown in option (b), where the phenyl and cyclohexyl groups are on opposite sides of the epoxide plane with the depicted H atoms on the same side. Why option (a) fails: Option (a) shows a cis-epoxide (Ph and Cy on the same face with oxygen on the bottom), which would arise from epoxidation of a cis-alkene. The dissolving metal reduction gives trans-alkene, not cis. Why option (c) fails: PhCO-Cy would require oxidative cleavage or a different reaction pathway, not simple epoxidation. Why option (d) fails: Ph-CH2-CO-Cy is a ketone product from rearrangement/hydration, not direct epoxidation. Therefore, the correct answer is B.