See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Concept: Resolution of a racemic carboxylic acid using an enantiomerically pure chiral amine works by forming diastereomeric salts that can be separated. For this to be possible, the acid must be chiral (exist as non-superimposable enantiomers) and must be racemic (a mixture of both enantiomers). Step 1 - Identify the source of chirality in each option: Options (a) and (b) are polycyclic or benzene ring systems with substituents. For these to be chiral without a stereocenter, they would need to be axially chiral (atropisomers) or have some other element of chirality. However, (a) is a naphthalene with substituents that appear symmetrically placed, giving a plane of symmetry and making it achiral (meso or symmetric). (b) is a benzene ring with two NO2 and two CO2H groups placed symmetrically, also possessing a plane of symmetry - achiral. Step 2 - Analyze option (c): Option (c) is a biphenyl compound with the following substitution: each phenyl ring bears one NO2 group and one CO2H group at the ortho positions (2,2'-dinitro-6,6'-dicarboxybiphenyl). In this biphenyl, the ortho substituents (NO2 and CO2H) on both rings are large enough to restrict rotation around the central C-C bond (atropisomerism). Crucially, the two rings each have DIFFERENT substituents at their two ortho positions (one CO2H, one NO2), and the substitution pattern is such that the molecule lacks a plane of symmetry perpendicular to the biphenyl axis. This gives rise to axial chirality - the molecule exists as two non-superimposable mirror-image atropisomers (Ra and Sa). Since it is a carboxylic acid and is chiral, it can be resolved by forming diastereomeric salts with an enantiomerically pure chiral amine. Step 3 - Analyze option (d): Option (d) is a 9,10-dihydroanthracene derivative with CO2H and NO2 on the same or different rings. The structure shown appears to have a plane of symmetry or lacks a proper stereogenic element to produce stable enantiomers under normal conditions, making it either achiral or not resolvable by this method. Step 4 - Why other options fail: (a) The naphthalene dicarboxylic acid with symmetric nitro substitution has an internal plane of symmetry - achiral, cannot be resolved. (b) The benzene dicarboxylic/dinitro compound has symmetric substitution with a plane of symmetry - achiral, cannot be resolved. (d) The dihydroanthracene derivative does not have stable axial chirality or a classical stereocenter that would allow resolution into stable enantiomers. Step 5 - Conclusion: Only option (c), the 2,2'-dinitro-6,6'-diphenic acid (biphenyl-2,6,2',6'-tetrasubstituted with NO2 and CO2H), possesses axial chirality due to restricted rotation around the biaryl bond and non-equivalent ortho substituents. It exists as stable Ra and Sa enantiomers that can be resolved by treatment with an enantiomerically pure chiral amine to form separable diastereomeric ammonium salts. Therefore, the correct answer is C.