Question

Explain, based on the corresponding ultraviolet spectra, why dibenzalacetone is found to be yellow, even though its starting reagents are colorless.

Please indicate why the reaction between acetone and 2-pentanone would not be a good method of preparing 4-methyl-3-hepten-2-one.

Write the reaction of the condensation of benzaldehyde with acetophenone.
Suggest a way to modify the laboratory procedure so that the reaction produces benzalacetone instead of dibenzalacetone.

Answer 1

Dibenzalacetone is a highly potent chemical that absorbs UV rays, making it the ideal ingredient for sunscreens. These conjugated dienes absorb light in the visible spectrum and in this case, it happens to be pale yellow. It is because of the conjugated dienes. i.e. Double bond C single bond C double bonds. C=C-C=C etc. These conjugated dienes absorb light in the visible spectrum and in this case, it happens to be pale yellow.