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Hydrogen bonds and structure of drug Xymedone in different phase and aggregate states were studied using IR and Raman spectroscopy, IR microscopy, quantum chemical calculations (B3LYP/6-31G*), X-ray powder diffractometry, and DSC and TGA methods. It was found that the synthesized specimen of Xymedone powder is a mixture of two gauche-conformers. First one is bound by intermolecular hydrogen bonds and second one is stabilized by an intramolecular hydrogen bond. Upon the dissolution of Xymedone the conformational equilibrium shifted in favor of conformers of the first or second type depending on the solvent nature.

The drug, dimephosphone, in aqueous media has two most probable conformers. The formation of hydrogen bonds with water and complexes with SnCl4 in acetonitrile involves the phosphoryl oxygen atom. Complexation favors some of the dimephosphone conformers.

The molecular mechanics method has been used to determine the equilibrium geometric parameters of 39 conformations of the 1,3,2,6-dioxaphosphazocine molecule, among which the preferred form is the boat-boat (BB) conformer with C and O atoms at the vertices. The role of the anomeric effect in stabilizing the axial orientation of the P-S bond has been evaluated quantitatively in various conformers on the 1,3,2,6-dioxaphosphazocine molecule.

1. 2-Chloro-1,3,2-dioxaphosphepane exists as at least two confomers or groups of conformers which are in thermodynamic equilibrium. 2. For 2-chloro-1,3,2-dioxaphosphepane, 11 conformers are possible. The most probable equilibrium forms were chosen from a comparison of the experiment and the calculation. 3. The predominant ring conformation in the case of d,1-2-chloro-4,7-dimethyl-1,3,2-dioxaphosphepane is similar to the ring conformation of 2-chloro-1,3,2-dioxaphosphepane and has 4e,7e orientation of the CH3 groups. The meso form of 2-chloro-4,7-dimethyl-1,3,2-dioxaphosphepane has predominantly a chair form with 4e,7e substitution.

1. The existence of a thermodynamic equilibrium between the trans and gauche conformers in ethyldichlorophosphonate, ethyldichlorothiophosphonate, and ethyldichloroselenophosphonate has been established. 2. The gauche conformer predominates in compounds I–III at 298°K. In the case of ethyldichlorophosphonate the trans isomer remains in the solid phase, in the thio analog the gauche isomer remains, and in the selenium analog the trans and gauche isomers remain. 3. The experimentally observed difference in the frequencies of the conformers is close to that calculated under the assumption that their force fields are constant. Nevertheless, the frequencies of the stretching vibrations of the multiple bonds are higher in the trans isomers than in the gauche. 4. One vibration with predominant participation of the P=X bond (ν P=O,ν P=S, andν P=Se) has been isolated in the spectrum of each conformer. The characteristic nature of the vibrations for the bonds just cited decreases along the series indicated.

1. According to a calculation by the methods of molecular mechanics, the realization of only one conformation with an axial P-Cl bond is possible for 2-chloro-1,3,2-dioxaphospholane and 2-chloro-1,3,2-dithiaphospholane in accordance with the experimental data. In 2-chloro-1,3, 2-dioxaphospholane this form is close to an envelope with an 0 atom departing from the plane of the other four atoms in the ring (a-Eo), and in the dithia analog a conformation which is close to an envelope with a C atom departing from the plane (a-Ec) is realized. 2. According to the data from the calculation, 2-chloro-1,3,2-oxathiaphospholane should exist in the form of ana-EC ⇄ e-Ec mixture of conformers (or with the participation of twist forms).

1. An equilibrium of conformers with gauche- and trans-orientation of the P = S and OCH3 groups in the gas and liquid phases follows from the vibrational spectra and dipole moments of methyldichloro-thiophosphate. A trans-conformer is realized in the crystalline state. 2. The IR and Raman spectra of methyldichlorothiophosphate were interpreted on the basis of a calculation of the frequencies and forms of the normal vibrations considering possible rotational isomers.

1. The IR and Raman spectra of the methyl selenophosphonates and methyl selenophosphinates: (CH3O)2P(Se)CH3, CH3OP(Se) (C2H5)2, and CH3OP(Se) (C6H5)2 were studied in various phase states and in solvents, and with a variation in the temperature. The vibration bands of the P=Se group were assigned. 2. A thermodynamic equilibrium of at least two steric forms of the molecule was detected in the first two compounds. The isomers arise as the result of one methoxy group rotating from the gauche position with respect to the P=Se bond to the trans position, with a gauche orientation of the other groupings. 3. The relative amount of the isomers in the mixture and the thermodynamic parameters of the equilibrium were determined. 4. The steric conditions created by the two aryl radicals in the third compound lead to a stabilization of one predominant conformer in all of the states of the compound, with a gauche orientation of the OCH3 with respect to the P=Se bond.

1. The 2-seleno-2-methyl- and 2-seleno-2-methyl-5,5-dimethyl-1,3,2-dioxaphosphorinanes in the liquid state (melt) and in solution exist as a mixture of two conformers with the structure of a distorted chair, which differ in the orientation of the P=Se bond. The energetically more favorable and quantitatively predominant, and also realized in the crystal, is the less polar form with an axial P=Se bond. 2. The vibrational spectra of the indicated compounds were interpreted on the basis of the experimental data and calculation.