Use of semiempirical methods for the prediction of equilibrium geometries and ionization potentials of 4h-pyran-4-one and sulphur analogues

Abstract

Equilibrium geometries and ionization energies of 4H-pyran-4-one ( I) 4H-pyran-4-thione ( II), 4H-thiapyran-4-one ( III) and 4H-thiapyran-4-thione ( IV) are calculated by CNDO/2 and MINDO/3 semiempirical methods. The geometries obtained are compared to the MW data available for I, II and IV. Reliability of geometry optimization and predictions based on semiempirical results are discussed. For I the vertical ionization energies estimated from ab initio, CNDO/2 and MINDO/3 orbital energies are compared to each other and to those obtained by HAM/3 calculations. The HAM/3 results are in the best agreement with the experimental data. For systematic HAM/3 studies on molecules for which no experimental geometries are available, the use of CNDO/3 or MINDO/3 optimized geometries is suggested.