Molecular Properties of 9,10-Phenanthrenequinone and Benzil

Phenanthrenequinone(PQ) and benzil are important α-diketones. This manuscript explains the first comparison of PQ and benzil molecular properties. We have used 1 H NMR, 13 C NMR, 1 H- 1 H COSY, HMBC, HMQC, UV-Vis absorption and emission, CV and TGA experiments to study PQ and benzil that provided the following novel results. (1) The 1 H NMR(CDCl3) of PQ show δ 8.19(H1), 8.02(H4), 7.72(H3), 7.47(H2) instead of an earlier reported δ 8.25(H4), 8.08(H1), 7.80(H2), 7.55(H3); (2) in the 13 C NMR(CDCl3), the C9/C10(C=O) signal of PQ appears upfield(δ 180.3) compared to C9/C10(C=O) signal of benzil(δ 194.5), which shows higher electrophilic character(more attrac- tive for nucleophiles) of C9/C10(C=O) of benzil; (3) the first λmax for the UV-Vis absorption and emission of PQ are blue-shifted compared to benzil despite increased conjugation attributed to the different symmetries(C2v for PQ and C2h for Benzil) of the two molecules; (4) the emission spectrum of benzil is broader compared to that of PQ due to slower relaxation of the excited state; (5) The CV study shows that PQ and benzil are good electron acceptors and PQ shows a better reduction process than benzil due to an extra ring that provides stability for the reduced species(mono or diradical anions); (6) TGA shows the higher thermal stability of PQ than benzil attributed to the presence of phe- nanthrene unit in PQ. Keywords 9,10-Phenanthrenequinone; Benzil; Molecular property; Electrochemistry Article ID 1005-9040(2009)-06-950-07