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Conformational analysis of tris(2-pyridyl)phosphine and tris(2-pyridyl)phosphine chalcogenides was carried out by the method of dipole moments and density functional theory calculations. The conformations of the examined compounds fit into the overall conformational picture for the P III and P IV compounds: namely, these phosphines have non-eclipsed gauche- and trans -forms with propeller arrangement of the pyridyl radicals about the P = Y bond (Y = lone pair, O, S, Se).

The structure of silatranes N[CH 2 (RMeC 6 H 2 )O] 3 SiR 1 with planar fragments in six-membered semi-rings was established by the methods of dipole moments and density functional theory calculations. They are endo-structures with transannular interaction N → Si in which the oxygen atoms located adjacent to the silicon participate besides the nitrogen and silicon atoms.

Structure of 1,4-heterophosphinanes in solution was studied by the methods of dipole moments, Kerr effect, molecular mechanics, and density functional theory calculations. It was determined that chair conformation with an equatorial orientation of the exocyclic phenyl substituent is preferred for 1,4-heterophosphinanes independent of the second heteroatom in six-membered phosphorus heterocycle (oxygen, sulfur or silicon), and the coordination state of the phosphorus atom (σ3P or σ4P).

The structure of a great number of methylenephosphine oxides 1-11 and cyanophosphines and their oxides 12-18 was studied by semiempirical PM3 and ab initio RHF/6-31G** calculations. Obtained results are in good agreement with experimental data (dipole moments, Kerr effect, IR spectroscopy). In 12-18 the contribution of interactions of CN group or Ph ring with lone pair of electrons (LPE) of the P atom, d-orbitals of the P atom, or P=O group is absent.