See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

A meso compound is an achiral molecule that contains two or more stereocenters but has an internal plane of symmetry, making it superimposable on its mirror image. Option (a): 2,3-dibromobutane. The Fischer projection shows H and Br on the same side at both stereocenters (both Br on the right). This is the meso form of 2,3-dibromobutane. The molecule has an internal plane of symmetry between C2 and C3 because the top half (CH3, H, Br) is the mirror image of the bottom half (CH3, H, Br). This IS a meso compound. Option (b): 3,4-hexanediol. The Fischer projection shows H and OH on the same side at both stereocenters (both OH on the right). The molecule has CH2CH3 groups at both ends. Due to the identical substituents at each stereocenter and the same configuration, there is an internal plane of symmetry between C3 and C4. This IS a meso compound. Option (c): cis-1,2-cyclopropanediol. The cyclopropane ring with both OH groups on the same face (both pointing down/front in wedge notation) and both H groups pointing up represents the cis isomer. The cis-1,2-cyclopropanediol has an internal plane of symmetry (a mirror plane bisecting the C1-C2 bond perpendicular to it, passing through C3). The two stereocenters have opposite configurations (one R, one S), making it a meso compound. This IS a meso compound. Since all three structures (a), (b), and (c) are meso compounds — each containing two stereocenters with an internal plane of symmetry rendering the molecule achiral — option (d) All of these is correct. Therefore, the correct answer is D.