Assuming that compound a has only c, h, and one n atoms, determine the molecular formula, and then draw a possible structure if compound a has ir absorption at 1620-1680 cm-1 but not at 3010-3090 cm-1

The peak at 1620-1680 cm⁻¹ is characteristic absorption peak of C=C stretching while peak at 3010-3100 cm⁻¹ is characteristic absorption peak of C-H streching in which C is sp² hybridized.

It means that the structure contains carbon double bond carbon but there is no H attached to sp² hybridized carbon.

I have drawn one structure which follows the scenario. And molecular formula of Molecule is C₆H₉N.

Result:
           According to given information the best suggested compound has formula C₆H₉N with structure shown below,