Question

Why is cinnamaldehyde slightly yellowish in color? What color of light is most likely absorbed by the compound?

Answer 1

Ans. Basically the absorption of the cinnamaldehyde is due to the π → π* transition. The presence of conjugation in cinnamaldehyde shifts it to visible range, due to which it appear colored. Conjugated systems have closer ground states and excited states of the electrons than for nonconjugated systems. Therefore, lower energy light is needed to excite electrons in conjugated system. More the conjugation in the system, lower will be the energy difference and the lower the required energy of light needed to excite the electrons. So, molecules having more conjugated multiple bonds absorb lower energies of light than do molecules having fewer conjugated multiple bonds.

The color that is reflected is the complementary color of the color that is absorbed. It will absorb indigo color of visible light and reflect back yellow.