J. Chem. Ed., submitted.

© W.J. Leigh

A Better Sunscreen – Conformational Effects on Spectral Properties.

Lawrence A. Huck and William J. Leigh*

Contribution from the Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West, Hamilton, ON Canada L8S 4M1.

A modification to the mixed-aldol synthesis of dibenzalacetone (1, prepared from acetone and benzaldehyde) is described wherein acetone is replaced with a series of cyclic ketones (ring size 5-7). The structural variations in the resulting conjugated ketones produce regular variations in the UV-vis absorption spectra. The choice of the best sunscreen agent based on these variations is straightforward, and by considering simple molecular orbital diagrams in the context of the molecular geometries, students can go the next step and understand why the variation occurs.

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