Which of the following is metamer of the given compound (X) ?

Solution

Chemistry ma’am · 3 steps

Keep the amide group fixed and swap the two rings across it: that swap is metamerism.

1. What a metamer is. Metamers have the same molecular formula and the same functional group. They differ only in which groups sit on either side of a polyvalent group such as -CO-NH⁻, -O⁻ or -CO-O⁻.
2. Read compound X. X is a cyclohexyl group on the carbonyl side and a phenyl group on the nitrogen side: C₆H₁₁-CO-NH-C₆H₅. Its formula is C₁₃H₁₇NO, and the functional group is a secondary amide.

   Compound	Formula	Functional group	Relation to X
   X: C₆H₁₁-CO-NH-C₆H₅	C₁₃H₁₇NO	amide	given
   (a) OHC-C₆H₄-NH-C₆H₁₁	C₁₃H₁₇NO	aldehyde + amine	functional isomer
   (b) C₆H₅-CO-NH-C₆H₅	C₁₃H₁₁NO	amide	not an isomer
   (c) C₆H₅-CO-NH-C₆H₁₁	C₁₃H₁₇NO	amide	metamer
   (d) C₆H₁₁-CO-NH-C₆H₁₁	C₁₃H₂₃NO	amide	not an isomer

3. So. In (c) the phenyl ring has moved to the carbonyl side and the cyclohexyl ring to the nitrogen side. The formula and the amide group stay the same, so (c) is the metamer of X.

The idea to keep. First check the molecular formula, then check the functional group. Same formula and same group with the pieces redistributed around it is metamerism; a different group is functional isomerism.

Answer from the NTA final answer key. Solution by PrepWiser.