Electronic and spatial structures of some derivatives of 5-phosphoranylidenbarbituric and 5-phosphoranylidenthiobarbituric acids

Abstract

The spatial and electronic structures of some derivatives of 5-phosphoranylidenbarbituric and 5-phosphoranylidenthiobarbituric acids are investigated within the framework of the semiempirical MNDO approximation. The effect of the substituents at the phosphorus and nitrogen atoms on the geometry and distribution of electron density in the studied molecules is considered. Their pseudoaromatic π-system, which is formed by diffuse lone electron pairs of the$\begin{array}{*{20}c} \backslash \\ / \\ \end{array} C^ - -$ ion and two N atoms, involves alternating donor and acceptor centers. The pseudoaromatic fragment in these molecules is nearly planar, and the deviations from planarity are dependent on the size of the substituents at the phosphorus and nitrogen atoms.