See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 – Identify the stereocenters and sources of stereoisomerism in the molecule. The structure shown is 1-hydroxycyclohexan-4-ylideneacetic acid. It has two independent sources of stereoisomerism: (i) A chiral centre at C1 of the cyclohexane ring (bearing H on a wedge bond and OH on a dash bond, plus two ring carbons as different substituents). (ii) A trisubstituted exocyclic double bond at C4 (the =CH–COOH group), which can exist as E or Z (cis/trans) geometric isomers. Step 2 – Determine what the 'two possible stereoisomers' refer to. The question describes one specific structure (one configuration at C1 AND one geometry at the double bond). The two stereoisomers in question differ in either the configuration at C1 OR the geometry of the double bond — in either case they are NOT mirror images of each other (they differ in only one of two stereocenters/stereoelements while the other remains fixed, or they are a chiral-centre/geometric pair). Two stereoisomers that are not mirror images of each other are by definition diastereomers — wait, let us re-examine for enantiomers. Step 3 – Check for enantiomer relationship. Actually, consider the molecule more carefully. The exocyclic double bond =CH(COOH) makes C4 a sp2 carbon; the ring is symmetric about the C1–C4 axis. C1 has: OH, H, and two –CH2– chains leading to C4. Because the two chains from C1 to C4 pass through identical –CH2CH2– units on each side, the two ring arms are enantiotopic/identical in the absence of other stereocenters. Now consider the exocyclic double bond: the two substituents on the =CH end are COOH and H, and on the ring-carbon end they are the two ring halves (identical) — so actually the double bond is NOT geometrically isomeric (both sides of the ring carbon of the double bond bear identical –CH2– groups). Therefore the only source of stereoisomerism is C1. Step 4 – With only one chiral centre (C1), the two stereoisomers (R and S at C1) are non-superimposable mirror images → enantiomers. Step 5 – Eliminate other options. (b) Diastereomers: stereoisomers that are NOT mirror images — not applicable here since there is only one stereocenter. (c) Conformers: same connectivity, different rotation about single bonds (not stereoisomers) — not applicable. (d) Rotamers: a type of conformer — not applicable. The two stereoisomers arise solely from the one chiral centre at C1, making them enantiomers. Therefore, the correct answer is A.