See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Positional isomers are compounds that have the same molecular formula and the same functional groups but differ in the position of substituents on the carbon skeleton. Step 1: Analyze option (a). 2-methylphenol (ortho-cresol) and 4-methylphenol (para-cresol) both have the molecular formula C7H8O, both contain an -OH group and a -CH3 group on a benzene ring, differing only in the relative positions of these substituents (positions 1,2 vs 1,4). These ARE positional isomers. Step 2: Analyze option (b). 3-methylphenol (meta-cresol) and 4-methylphenol (para-cresol) both have the molecular formula C7H8O, both contain an -OH group and a -CH3 group on a benzene ring, differing only in substituent positions (1,3 vs 1,4). These ARE positional isomers. Step 3: Analyze option (c). Benzyl alcohol (C6H5-CH2OH) has molecular formula C7H8O. Anisole/methoxybenzene (C6H5-OCH3) also has molecular formula C7H8O. However, these two compounds differ not merely in the position of a substituent but in the nature/connectivity of the functional group: benzyl alcohol has a -CH2OH group (primary alcohol) attached to the ring, whereas anisole has an -OCH3 group (ether) directly on the ring. The oxygen is bonded differently in each structure, making them functional group isomers (metamers/functional isomers), NOT positional isomers. Step 4: Since option (c) represents a pair that are NOT positional isomers (they are functional group isomers), and options (a) and (b) are genuine positional isomers, option (d) 'All of these' is incorrect. Therefore, the correct answer is C.