Structural features of labile N-phosphorylammonium zwitterions and cations according to data from MNDO calculations and15N NMR spectroscopy

1.	A quantum-chemical study of the structure of the active phosphorylating derivatives of N-phosphorylammonium cations and zwitterions and of the model structures of N-phosphorylazides was undertaken in the MNDO approximation with the sp and spd basis sets.
2.	It is shown that the inclusion of the 3d Orbitals at the phosphorus atom is essential for the production of correct values for the length of the bond between the phosphorus atom and the quaternary nitrogen atom.
3.	According to the agreement between the results from the MNDO calculations and15N NMR spectroscopy, the length of the phosphorylammonium bond decreases appreciably in the transition from the zwitterion to the cation.

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya No. 6, pp. 1292–1297, June, 1989.