| Popis: |
Infrared spectra of coumarins (O, S, Se) and chromones (O, S, Se) in several solvents and of their complexes with Lewis-acids are examined. The carbonyl band of thio-1 and seleno-1 coumarins is complex, abnormally low and not pure. A methyl group in position 3 gives important lowering of the CO. Infrared spectra of thio-1 and seleno-1 coumarins are very similar and constitute a rapid identification of isologous seleno-1 coumarins. The thio-1 and seleno-1 chromones possess very different spectra, except the carbonyl region. There is doubt for the CS vibration because the formation of dithiocoumarins and thio-2 seleno-1 coumarins leads to 2 strong bands near 1000-1150 cm−1. The CC is approached by comparison of coumarins (O, S, Se) with thio-2 derivates. Interpretation of many results is possible by the hypothesis that a polar form occurs partly in thio-1 and seleno-1 coumarins, in dithiocoumarins and thio-2 seleno-1 coumarins, in thio-1 and seleno-1 chromones. |
