See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the relationship between the two structures. The left structure shows 1-chloro-2-methylcyclopentane with both CH3 and Cl on wedge bonds (both pointing toward the viewer, i.e., cis configuration). The right structure shows 1-chloro-2-methylcyclopentane with CH3 on a wedge bond and Cl on a dashed bond (trans configuration). Therefore, the two compounds are stereoisomers (diastereomers) of each other — they have the same molecular formula but different spatial arrangements. Step 2 - Determine what properties are identical for diastereomers. Diastereomers share the same molecular formula (same atoms and connectivity), so their molecular composition is identical. However, diastereomers have different physical properties such as boiling point and melting point, so options (b) and (c) are incorrect. Because they are different stereoisomers (cis vs. trans), they also have different IUPAC names (one is cis- and the other is trans-), so option (d) is incorrect. Step 3 - Confirm option (a). Both structures are C6H11Cl (cyclopentane ring + CH3 + Cl). The molecular composition (molecular formula) is identical for any set of stereoisomers, including diastereomers. Step 4 - Why other options fail. (b) Boiling point: diastereomers have different boiling points due to different intermolecular interactions and dipole moments. (c) Melting point: diastereomers have different crystal packing and therefore different melting points. (d) IUPAC name: cis-1-chloro-2-methylcyclopentane vs. trans-1-chloro-2-methylcyclopentane — these are different names. Therefore, the correct answer is A.