An unknown compound \(\mathrm{C}_{7} \mathrm{H}_{5} \mathrm{~N}\) on catalytic hydrogenation gave \(\mathrm{C}_{7} \mathrm{H}_{15} \mathrm{~N}\). Hydrolysis of the unknown converted it into an acid which on fusion with \(\mathrm{NaOH}\) yielded \(\mathrm{C}_{6} \mathrm{H}_{6}\). On catalytic hydrogenation this hydrocarbon gave \(\mathrm{C}_{6} \mathrm{H}_{12}\). Suggest a suitable structure for the unknown.

To calculate the degree of unsaturation, we use the following formula: Degree of Unsaturation = (2C + 2 - H - N) / 2 Where C is the number of carbon atoms, H is the number of hydrogen atoms, and N is the number of nitrogen atoms. For the unknown compound C₇H₅N: Degree of Unsaturation = (2 x 7 + 2 - 5 -1) / 2 = 5 For the product of the unknown compound after catalytic hydrogenation (C₇H₁₅N): Degree of Unsaturation = (2 x 7 + 2 - 15 - 1) / 2 = 0 For the hydrocarbon formed after hydrolysis and fusion with NaOH (C₆H₆): Degree of Unsaturation = (2 x 6 + 2 - 6 - 0) / 2 = 4 For the product of the hydrocarbon after catalytic hydrogenation (C₆H₁₂): Degree of Unsaturation = (2 x 6 + 2 - 12 -0) / 2 = 1

Since catalytic hydrogenation reduces unsaturation by converting double bonds and triple bonds to single bonds, we know that: - The unknown compound has 5 degrees of unsaturation before hydrogenation. - The hydrocarbon C₆H₆ formed after hydrolysis and fusion with NaOH has 4 degrees of unsaturation. The unknown compound reacts with hydrogen to form C₇H₁₅N, which has no unsaturation. This means that the unknown compound may have a combination of 5 double bonds, triple bonds, or aromatic rings. The compound's nitrogen must be saturated to account for 5 degrees of unsaturation. Since the hydrocarbon C₆H₆ formed after hydrolysis and fusion with NaOH has 4 degrees of unsaturation and further gets saturated to C₆H₁₂ after hydrogenation, it suggests that the C₆H₆ hydrocarbon has an aromatic ring as the main structural unit.

Considering the information from steps 1 and 2, it's probable that the unknown compound C₇H₅N has an aromatic ring (benzene) with a saturated nitrogen-containing functional group. We can assume that the unknown compound is an aniline derivative with one methyl group attached. Putting all pieces together, a suitable structure for the unknown compound can be proposed as p-methyl substituted aniline, also known as p-toluidine. The formula for p-toluidine is C₇H₅N, and its structure consists of an aromatic ring with an amino group (-NH₂) and a methyl group (-CH₃) attached in the para position. The reactions of the unknown compound, as described in the exercise, are consistent with the proposed structure of p-toluidine.