Abstract
Analysis of the aromatic region of the 1H NMR spectra of some phenyl substituted pentacoordinated compounds of main group elements (Si, Pb, P, As, Sb, S, Te, I) revealed a characteristic low-field multiplet, assignable to ortho protons, separated from a more intense high-field multiplet, assignable to the meta and para protons. The data imply that an increase in the magnitude of the multiplet separation may be correlated with a decrease in electronegativity of the central atom and an increase in electronegativity of attached ligands. These effects are consistent with a delocalization of the aromatic π electron density into vacant d orbitals of the central atom as well as a strengthening of the central atom sigma bond. The enhanced mutiplet separation for equatorially oriented phenyl groups in a trigonal bipyramid or axially oriented ones in a rectangular pyramid is diagnostic in indicating the presence of the pentacoordinated state for main group element compounds in solution.
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