CNDO/S-CI-flPDQ Studies of the Solvation Effect on the UV Spectra of Pyridine N-Oxide and its Complexes with Proton

U sing the w-PDQ model, in which the solvent is sim ulated by several point dipoles and quad ­ r u p le s , we have estim ated the shift o f the UV bands o f pyridine N-oxide (PyO), its cationic acid (PyO H +), and hom oconjugated cation (PyO H PyO +) caused by the solvent (acetonitrile). We have calculated the UV spectra o f both unsol­ vated and solvated species by the C N D O /S-C I and C N D O /S-C I-nPD Q method, respectively. We have found that all the bands o f all the species un­ der study are blue-shifted on solvation. The m ost significant is the shift of the long-wave n—*n* bands o f pyridine N-oxide.