Question

In an organic chemistry lab, the two starting reagents used were white and pure substances. Why does the product of the reaction yield a yellow substance?

Answer 1

two starting reagents are white in color means these two pure substances do not absorb any wavelength of visible range. But the product shows yellow color means it absorb the wavelength in purple/violet color . The substance emitts the complementary color of absorbed color.

Therefore, there is an electronic transition in product due to crystal field splitting or ligand metal charge transfer or metal ligand charge transfer or spin-spin transition. As a result the product absorb energy and color of the product is observed.