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Experimental and theoretical conformational analysis of N-methyl-N-[2-(diphenylphosphoryl)ethyl]diphenylphosphorylacetamide, N-butyl-N-[2-(diphenylphosphoryl)ethyl]diphenylphosphorylacetamide, and N-octyl-N-[2-(diphenylphosphoryl)ethyl]diphenylphosphorylacetamide was carried out by the methods of dipole moments, IR spectroscopy, and Density Functional Theory (DFT) B3PW91/6-311++G(df,p) calculations. In solution, these N,N-dialkyl substituted bisphosphorylated acetamides exist as a conformational equilibrium of several forms divided into two groups—with Z- or E-configuration of the carbonyl group and alkyl substituent, and syn or anti arrangement of the phosphoryl-containing fragments relative to the amide plane. The substituents at the phosphorus atoms have eclipsed cis- or staggered gauche-orientation relative to the P=O groups, and cis orientation of the substituents is due to the presence of intramolecular H-contacts P=O...H−Cphenyl or p,π conjugation between the phosphoryl group and the phenyl ring. Preferred conformers of acetamides molecules are additionally stabilized by various intramolecular hydrogen contacts with the participation of oxygen atoms of the P=O or C=O groups and hydrogen atoms of the methylene and ethylene bridges, alkyl substituents, and phenyl rings. However, steric factors, such as a flat amide fragment, the bulky phenyl groups, and the configuration of alkyl bridges, make a significant contribution to the realization of preferred conformers.

In the present work a thermochemistry of solution and solvation of mono- and di-substituted chloro- and nitrobenzenes in binary mixtures was studied. The infinite dilution solution enthalpies of 1,2-dichlorobenzene,1,4-dichlorobenzene, 1,2- dinitrobenzene, 1,4-dinitrobenzene, 1-chloro-2-nitrobenzene and 1-chloro-4-nitrobenzene in binary mixtures of benzene-cyclohexane, benzene-acetonitrile, carbon tetrachloride-acetonitrile at different molar ratios (0, 0.25, 0.50, 0.75, 1.00) solvents were measured at 298.15 K. Based on experimental data the solvation enthalpies in binary mixture were calculated. It was shown that the solvation enthalpies slightly depend on neither the location of chloro- and nitro - substituents in aromatic ring nor a composition of binary mixture.

The mechanism of reactions of silatranes and germatranes, and their bicyclic and monocyclic analogues with one molecule of methanol or ethanol, was studied at the Density Functional Theory (DFT) B3PW91/6-311++G(df,p) level of theory. Reactions of 1-substituted sil(germ)atranes, 2,2-disubstituted sil(germ)ocanes, and 1,1,1-trisubstituted hyposil(germ)atranes with alcohol (methanol, ethanol) proceed in one step through four-center transition states followed by the opening of a silicon or germanium skeleton and the formation of products. According to quantum chemical calculations, the activation energies and Gibbs energies of activation of reactions with methanol and ethanol are close, their values decrease in the series of atranes&ndash, ocanes&ndash, hypoatranes for interactions with both methanol and ethanol. The reactions of germanium-containing derivatives are characterized by lower activation energies in comparison with the reactions of corresponding silicon-containing compounds. The annular configurations of the product molecules with electronegative substituents are stabilized by the transannular N&rarr, X (X = Si, Ge) bond and different intramolecular hydrogen contacts with the participation of heteroatoms of substituents at the silicon or germanium.

Conformational analysis of derivatives of bis(2-phenylethyl)selenophosphinic acid 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 PIV compounds: these derivatives exist as conformational equilibrium of non-eclipsed gauche and trans forms with propeller arrangement of the substituents relative to the P=Se bond. We stipulate that the eclipsed cis orientation of substituent may be caused by the formation of H-contact.

The mechanism of the hydrolysis reactions of 2,2-dihydroxysilocane, 2,2-dihydroxygermocane, 1-hydroxysilatrane, and 1-hydroxygermatrane was studied by the density functional theory method. Accordin...

The mechanism of the reaction of 3,3-dimethyl-2-trimethylsiloxy-1-trimethylsilyl-1-phosphabut-1-ene with bis(phenylendioxy)chlorophosphorane was studied by the density functional theory method. Acc...

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 polarities of 2-chloro-N-(2-((diphenylphosphoryl)methyl)phenyl)acetamide and 2-chloro-N-(2-((diphenylthiophosphoryl)methyl)phenyl)acetamide were determined, and conformational analysis of these...

The structure of some six- and eight-membered phosphorus and silicon heterocycles was established by the method of dipole moments and density functional theory calculations. There are two necessary conditions for the feasibility of the transannular interaction in these heterocycles: (1) the favorable disposition of the donor and acceptor centers in a molecule and (2) the presence of the substituents with the considerable polarizing effect at the heteroatom.

Experimental and theoretical conformational analysis of polyfunctional 2-substituted nitroethenes was carried out by the method of dipole moments and density functional theory calculations. It was established that the nitro and ester (or trichloromethyl) groups are trans-arranged in the molecules of 2-trichloromethyl-(ethoxycarbonyl)-1-nitro- and 1-bromo-1-nitroethenes, i.e., nitroalkenes have E-configuration, their bromo-containing analogues have Z-configuration, and s-cis-orientation of the C=C and C=O double bonds is preferred for nitroacrylates. 2,3-Dibromo-3-nitroacrylates have untrivial Z-configuration in solution.

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).

Conformational analysis of 1,3,2-dioxaphospholane-2-yl-2,2,2-trifluoroacetate and 4,5-benzo-1,3,2-dioxaphosphole-2-yl-2,2,2-trifluoroacetate was carried out by dipole moment method and quantum chemical calculations (DFT B3LYP/6-31G*).

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.

A 1H NMR conformational study of cis- and trans-4-substituted cyclohexene oxides revealed an increased predominance, as compared with the parent 4-substituted cyclohexenes, of the equatorial conformer for cis-isomers and a preference of the axial conformer for trans-isomers. These conformational shifts can be rationalized in terms of intramolecular dipole-dipole and/or steric interactions. However, molecular mechanics calculations failed to reproduce the relative stability of the axial conformer in trans-4-substituted cyclohexene oxides.