Electronic structure of 4H‐pyrido[1,2‐a]pyrimidin‐4‐ones

The characteristic features of ir and uv spectra of 43 4H‐pyrido[1,2‐a]pyrimidin‐4‐one derivatives with electron donor or acceptor groups in position 3, and positions 6, 7, 8, or 9, respectively, have been systematically studied. On the basis of the spectra some conclusions have been drawn for the molecular structure. The negative solvent effect of the lowest‐energy π → π* transition is investigated by the PPP method.