|
Structures of 4H-pyran-4-one(I), 4H-pyran-4-thione(II), 4H-thiapyran-4-one (III), 4H-thiapyran-4-thione(IV) have been determined by MNDO and MINDO/3 methods. Geometries and physicochemical properties, especially the aromaticity, were found to agree well with the results of microwave experiments. The order of aromaticity was found to be (IV) > (III) > (II) > (I), which demonstrated inhibitory effect of strongly electronegative oxygen atom on the electron delocaligation, and the order of dipole moment, (II) > (IV) > (I) > (III), indicated the dominant contribution of the bond length of carbonyl group (C=O or C=S)
|