See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1: Identify the reaction sequence. Starting material: CH3-C≡C-H (propyne / methylacetylene) Step 2: Treatment with NaNH2 deprotonates the terminal alkyne to form the acetylide anion: CH3-C≡C^(-) Na^(+) Step 3: Treatment with CH3I (alkylation of acetylide) gives: CH3-C≡C-CH3, i.e., 2-butyne (an internal alkyne). This is compound (A). Step 4: Hydrogenation of 2-butyne (CH3-C≡C-CH3) over Pd-CaCO3 (Lindlar's catalyst) gives syn addition of H2, producing cis-2-butene (Z-2-butene). This is compound (C). Step 5: Identify compound (B). The question asks about the relation between (B) and (C). In the context of this problem, (B) is the product of reduction of 2-butyne under different conditions — specifically with Na/liquid NH3 (Birch-type, dissolving metal reduction), which gives trans-2-butene (E-2-butene) via anti addition. Although (B) is not explicitly shown in the cropped image, the standard paired question involves (B) = trans-2-butene from Na/NH3 reduction. Step 6: Relationship between (B) (trans-2-butene) and (C) (cis-2-butene). - Both have the molecular formula C4H8 and the same connectivity (but-2-ene), so they are stereoisomers. - They differ in the spatial arrangement of groups around the C=C double bond: one is cis (Z) and the other is trans (E). - Because of the restricted rotation about the double bond, they cannot interconvert without bond breaking, making them geometrical isomers (a type of stereoisomerism with restricted rotation). - They are also diastereomers: stereoisomers that are not mirror images of each other. Geometrical isomers (cis/trans about a double bond) are a subset of diastereomers. - Therefore, (B) and (C) are simultaneously geometrical isomers (option c) AND diastereomers (option b), since geometrical isomers are a specific type of diastereomers. Step 7: Why not (a) Enantiomers? Enantiomers are non-superimposable mirror images. cis- and trans-2-butene are not mirror images of each other. Why not (d) Meso? Meso compounds contain stereocenters but are achiral due to internal symmetry. Neither cis- nor trans-2-butene is a meso compound in the classical sense of that term (they lack stereocenters). Both (b) Diastereomer and (c) Geometrical isomer correctly describe the relationship, as geometrical isomers are a subclass of diastereomers. Therefore, the correct answer is B,C.