Ab initio molecular orbital calculations were performed on a series of phosphazene trimer molecules to elucidate the electronic structure of these systems. The role of the d orbitals was analyzed from comparison of the molecular orbital contour calculations performed both with and without d orbitals in a split valence basis set description. The results indicate that, although the major geometric aspects of these systems can be described without invoking the use of d orbitals, these orbitals are essential to properly describe the electronic structure. The d orbital involvement in out-of-plane T bonding contains elements of both the classical Craig, Paddock, and Mitchell [l-31 and Dewar et al.[4] bonding schemes; the d orbital effects on in-plane bonding modes are also substantial. The charge distribution in these systems is best described as a zwitterionic form, because a significant amount of charge accumulates on the ring nitrogens.

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SUMMARY Sera from various groups were tested for syphilis by cardiolipin, fluorescent treponemal antibody-absorbed (FTA-ABS), and treponemal haemagglutination (TPHA)

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