Photoelectron spectroscopy of biologically active molecules. 20.Para-quinones, semiquinones, and aromatic ketones

Abstract

We have recorded and analyzed the HeI PE spectra of the following molecules: 9,10-dihydroanthracene (1); 9,10(H)-anthracenone (2); 9,10-anthracenedione (3); 1,2,3,4-tetrahydro-9,10-anthracenedione (4); 1,4,1a,4a-tetrahydro 9,10-anthracenedione (5); 10-methylene-9,10(H)-anthracenone (6); and 10-(phenylmethylene)-9,10(H)-anthracenone (7). The PE spectra are assigned by comparison with those of the composite parts (i.e., by employing an orbital interaction model such as the composite molecule method). This approach, which works surprisingly well in the present instance, indicates that the carbonyl lone pair and the carbonyl π electrons interact negligibly with the outer π electrons of the aromatic unit(s). If no change in conformation of the component aromatic parts occurs, the spectrum of the composite molecule exhibits the additivity property. This result agrees with previous studies of benzophenones [3]. However, it is argued that the ordering of the strongly overlapped, low energy ionization bands of benzaldehyde and acetophenone should be changed to I1(π), I2(π) ≈︁ I3(no) and I1(π), I2(no), I3(π), respectively.