Identifying structural isomers via molecular formulas

Steps:

• Determine the molecular formula for each compound in the pairs.
• Compare formulas within each pair to check if they match.
• Confirm matching pairs have different connectivity for isomerism.
• Select the pair with identical formulas but distinct structures.

Why C is correct:

• Both 3-methylbutan-2-one (CH₃COCH(CH₃)CH₃) and pentanal (CH₃CH₂CH₂CH₂CHO) have the formula C₅H₁₀O, with ketone and aldehyde functional groups confirming structural isomerism.

Why the others are wrong:

• A: 2,2-Dimethylpropanoic acid is C₅H₁₀O₂; propyl methanoate is C₄H₈O₂—formulas differ.
• B: 2-Methylpropan-1-ol is C₄H₁₀O; hexan-3-ol is C₆H₁₄O—formulas differ.
• D: 3,3-Dimethylbutan-1-ol is C₆H₁₄O; pentan-3-ol is C₅H₁₂O—formulas differ.

Final answer: C