MO study of molecular and electronic structure of 2H and 4H-pyrans

CNDO/2, STO-3G and 4-31G MO calculations have been carried for the molecules I-IV. Their molecular and electronic structure is discussed with respect to relative stabilities of the respective compounds and valence isomerism I III. Significance of application of the split-valence base in the ab initio MO calculations carried out is demonstrated.