Quantum-chemical study of chlorophosphoranes: I. Structure of the (C<Subscript>6</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>PCl<Subscript>3</Subscript> molecule in gaseous and crystalline states

The quantum-chemical calculations of the (C₆H₅)₂PCl₃ molecule were performed by the methods RHF/6-31G(d) and MP2/6-31G(d) with complete and partial optimization of its geometry. The results of calculations were used for evaluating the NQR frequencies of ³⁵Cl and the parameters of asymmetry of the of electric field gradient on the ³⁵Cl nuclei of this molecule. According to the results of calculations with the partial optimization of geometry and to the experimental data of ³⁵Cl NQR the bond lengths were found of central atom P in the solid state of this compound. The mutual influence of its axial and equatorial bonds was studied. It is shown that in chlorophosphoranes the ³⁵Cl NQR frequencies of the axial and equatorial chlorine atoms decrease with the decrease in the bond lengths of phosphorus atom.     

Quantum-chemical study of chlorophosphoranes: II. Structure of molecules of (Cl2)aP(ClnX3?n)e series, and mutual influence of axial and equatorial substituents

The quantum-chemical calculations of the (C₆H₅)₂PCl₃ molecule were performed by the methods RHF/6-31G(d) and MP2/6-31G(d) with complete and partial optimization of its geometry. The results of calculations were used for evaluating the NQR frequencies of ³⁵Cl and the parameters of asymmetry of the of electric field gradient on the ³⁵Cl nuclei of this molecule. According to the results of calculations with the partial optimization of geometry and to the experimental data of ³⁵Cl NQR the bond lengths were found of central atom P in the solid state of this compound. The mutual influence of its axial and equatorial bonds was studied. It is shown that in chlorophosphoranes the ³⁵Cl NQR frequencies of the axial and equatorial chlorine atoms decrease with the decrease in the bond lengths of phosphorus atom.     

Stereoelectronic srtructure of γ-chloropropyltrichlorostannane. <Emphasis Type="Italic">Ab initio</Emphasis> calculation

The quantum-chemical calculations by the RHF/3-21G* and MR2/3-21G* methods of the Cl(CH₂)₃SnCl₃ and ClCH₂SnCl₃ molecules with full optimization of their geometry was performed. The Cl(CH₂)₃SnCl₃ molecule was also calculated by the RHF/3-21G* method at different distances between the Sn atom and the Cl atom in the C-Cl fragment. From the results of the calculations ³⁵Cl NQR frequencies were estimated and the electric field gradient asymmetry parameters at the ³⁵Cl nuclei of these molecules. The abnormally high electron density on the Cl atom of the C-Cl fragment in the Cl(CH₂)₃SnCl₃ molecule is due mainly to the polarization of this compound under the influence of significant positive charge on the Sn atom directly through the field. The polarization of the C-Cl bond in the molecule is of the opposite direction to the polarization of the related bond in the ClCH₂SnCl₃ molecule because of the peculiarities of their geometries. The transfer of the electron density from the Cl atom of the C-Cl fragment to the Sn atom in the Cl(CH₂)₃SnCl₃ molecule is not observed.     

Special Features of the Geometry of the 2,2,2,4,4,4-Hexachloro-1,3-dimethyl-1,3-diaza-2,4-diphosphetane Molecule and Its Electron Distribution According to Data of ab initio Calculations

The results of a nonempirical calculation of the 2,2,2,4,4,4-hexachloro-1,3-dimethyl-1,3-diaza-2,4-diphosphetane (Cl₃PNCH₃)₂ molecule by the RHF 6-31G(d) method are in agreement with the data of X-ray structural analysis of this compound. Calculated ³⁵Cl NQR frequencies for axial and equatorial chlorine atoms are close to the experimental values. The population of the orbitals of the lone electron pairs and the p orbitals of the equatorial Cl atoms were significantly lower than those of the axial atoms. Among the MO there was no MO corresponding to a three-center bond involving a P atom and axial Cl and N atoms.     

Structure of N-chloromethyllactams and features of the interaction of atoms in them as a result of ab initio calculations

Quantum-chemical calculations have been carried out by the RHF/6-31G(d) and MP2/6-31+G(d) methods of molecules of N-chloromethylpyrrolidone, N-chloromethylcaprolactam, N-chloromethyl-succinimide, and N-chloromethylphthalimide with full optimization of their geometry, and also N-chloromethylpyrrolidone molecule by the RHF/6-31G(d) method at various angles of rotation of the CH₂Cl group around the C―N bond. It was shown that the lower frequencies of the ³⁵Cl NQR of the first two molecules in comparison with the later are mainly determined by the high populations of the p _σ -orbitals of their Cl atoms. The population of the orbitals of the unshared electron pair of the N atom is practically unchanged on rotating the CH₂Cl group, but the N atom polarizes the C―Cl bond in the indicated molecule. This does not confirm the supposed p,σ*-conjugation in the Cl―C―N grouping. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1537–1544, October, 2008.     

Effect of the Carbonyl Group on the C-Cl Bonds in 2,2-Dichlorocyclohexanone and Some Model Molecules, According to ab initio Calculations

Ab initioRHF/6-31G(d) calculations of 2,2-dichlorocyclohexanone, chloropropanone, and chloroacetaldehyde molecules were performed. In 2,2-dichlorocyclohexanone, the carbonyl group exerts different effects on the axial and equatorial C-Cl bonds. At rotation of the C(O)CH₃ group in chloropropanone and C(O)H group in chloroacetaldehyde around the C-C bond, the population of the 3p component of the chlorine valence p _z orbital varies in the opposite direction with the calculated ³⁵Cl NQR frequency and, in the case of chloroacetaldehyde, with the charge on the oxygen atom.     

Mutual influence of axial and equatorial P-Cl bonds in the molecular forms of pentachlorophosphorane,their lengths in gaseous and crystalline states

The quantum-chemical calculations by RHF/6-31G(d), MR2/6-31G(d) and MP2/6-31+G(d) methods of molecular forms of pentachlorophosphorane with the complete geometry optimization at the different lengths of P-Cl bonds are performed. The results of the calculations are used for estimation of respective ³⁵Cl NQR frequencies. The lengths of axial (2.05 Å) and equatorial (2.01 Å) P-Cl bonds are found, when the calculated NQR frequencies of Cl atoms practically coincide with the obtained experimentally at 77 K. These bonds are a little shorter than in the gaseous state of the matter. In contrast to the ratio of the lengths of the experimental P-Cl bonds and NQR frequencies of respective Cl atoms, at the use of increased lengths of these bonds in the quantum-chemical calculations of the molecule, the ³⁵Cl NQR frequencies of Cl atoms calculated from the results of these calculations, increase. Therewith, the change in the length of the equatorial P-Cl bonds with unchanged length of axial bonds leads to a significantly greater change in the NQR frequencies of axial chloroine atoms than of the equatorial, and vice versa.     

Geminal interactions in ClZ(CH3)2X molecules (Z = C, Si, Ge) according to ab initio calculations

The structure and electronic parameters of ClZ(CH₃)₂X molecules (Z = C, Si, Ge, X = CH₃, OCH₃) were calculated by the RHF/6–31G(d) and RHF/6–311G(d,p) methods with full geometry optimization; calculations of ClZ(CH₃)₂OCH₃ molecules were also performed by the RHF/6–31G(d) method with partial geometry optimization. The ³⁵Cl NQR frequencies calculated from the populations of less diffuse 3p constituents of valence p orbitals of chlorine [RHF/6–31G(d)] were in agreement with the experimental values. The ³⁵Cl NQR frequencies for molecules with X = OCH₃ are lower than those for molecules with X = CH₃ (the Z atom being the same), due mainly to direct through-field polarization of the Z-Cl bond, induced by the effect of unshared electron pair of the oxygen atom in the trans position with respect to that bond. The difference in the ³⁵Cl NQR frequencies decreases in going from Z = C to Z = Si, Ge, in parallel with variation of the Z-Cl bond polarization as the size of Z increases.     

Ab initio calculations of atomic interaction in the ClCH2OCH3 molecule

Ab initio calculations of both ClCH₂OCH₃ and ClCH₂CH₃ molecules and various ClCH₂OCH₃ structures with fixed angles of rotation of the methoxy group about the C−O bond were performed by the restricted Hartree-Fock method in the valence-split 6–31 G^* basis set with full optimization of the geometry. The populations of the valent p-orbitals of the chlorine atoms in these molecules have been analyzed. The³⁵Cl NQR frequencies and the asymmetry parameters of the electric field gradient (EFG) at the³⁵Cl nuclei have been calculated. Good agreement with experimental NQR frequencies was obtained for the calculations where only the populations of the less diffuse 3p-components of these orbitals were used. The³⁵Cl NQR frequency in ClCH₂OCH₃ is lower than that in ClCH₂CH₃ due to the higher population of the less diffuse component of the p_σ-orbital of the Cl atom in the former molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 431–434, March, 1997.     

Conformational Features of Monochloro-substituted Tetrahydropyrans According to Data from <Emphasis Type="Italic">ab initio</Emphasis> Calculations and <Superscript>35</Superscript>Cl NQR

Nonempirical quantum-chemical calculations of 2-, 3-, and 4-chloro-substituted tetrahydropyrans by the RHF/6-31G(d) and MP2/6-31G(d) methods showed that their conformational energy increases in the transition from the 4- to the 3-chloro-substituted compound, while in the transition to the 2-substituted compound the sign changes. In each of these isomers the axial C-Cl and C-H bonds, situated in the geminal position in relation to the oxygen atom, are longer, while the electron density at their Cl and H atoms is higher than in the corresponding equatorial bonds.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 196–201, February, 2005.     

35Cl NQR Spectra and ab initio Calculations of gem-Substituted 1-Chlorocyclohexane Derivatives

The ³⁵Cl NQR spectra of gem-substiutted 1-chlorocyclohexane derivatives C₆H₁₀XCl (X = H, CH₃, CH₃O, Cl) at 77 K were measured. Ab initio RHF/6-31G(d) calculations of their conformers, and also of conformers of monosubstituted cyclohexanes were performed. Based on the calculation results, the NQR lines were assigned and the conformational energies of the substituents were evaluated. The relative conformational energies of the Cl atom and CH₃O group disagree with previous data.     

Stereoelectronic structure of 1-methyl-3-(trichlorogermyl)propionic acid as found by <Emphasis Type="Italic">Ab initio</Emphasis> calculations

Calculations of three structures of the 1-methyl-3-(trichlorogermyl)propionic acid molecule and its dimers were performed at the RHF/6-31G(d) level with the full geometry optimization. According to the calculations, in this molecule in a gaseous state the Ge atom is most likely pentacoordinated due to the Ge←O coordination interaction. The dimerization does not diminish, but slightly increases the strength of Ge←O coordination bond. At the formation of the Ge←O bond the electron density on the oxygen atom increases and on the Ge atom decreases. The comparison of the results of calculations with X-ray diffraction data and with the ³⁵Cl NQR spectrum shows that stereoelectronic structure of this compound in the crystalline and gaseous states are quite different.     

ab initio Calculation of the stereoelectronic structure of 1-(1-trichlorogermylethyl)-pyrrolidin-2-one*

RHF/6-31G(d) and MP2/6-31G(d) calculations were carried out to study the stereoelectronic structure of 1-(1-trichlorogermylethyl)pyrrolidin-2-one with a pentacoordinated germanium atom. These results were compared with the X-ray diffraction structural analysis data. Upon formation of the Ge ← O coordination bond in this molecule, the electron density of all the atoms of the coordination polyhedron of the germanium atom, including the oxygen atom, increases, especially the axial chlorine atom, while the electron density of the germanium, nitrogen, and carbonyl group carbon atoms decreases. Different polarization of all three valence p-orbitals of each Cl atom of this molecule was established. ³⁵Cl nuclear quadrupole resonance spectrum parameters were evaluated. The molecule also has stable form, in which the germanium atom is tetracoordinated. The total energy of this form is 2.7 kcal/mol higher than for the structure with a pentacoordinated germanium atom.     

Molecular structure and conformational transitions of dichloroacetylchloride

RHF and MP2 techniques in 6–31G(d) basis set have been used to determine the structure of the isolated molecule CHCl₂COCl in two stable conformations (cis-and gosh-), as well as in transition states arising due to the rotary motion of CHCl₂ group around the C—C bond. The energy gap between the conformers and the relevant potential barriers has been calculated using the obtained potential dependence of the internal rotation. Plausible conformation of dichloroacetylchloride is discussed on the basis of ³⁵Cl NQR.     

Nonempirical approach to the conformational analysis of 2,4-dimethyl-1,3,2-dioxaborinane and its oxonium ions

Using nonempirical quantum-chemical approximations RHF//STO-3G, 3-21G, 6-31G(d) and MP2//6-31G(d,p) a conformation isomerism of 2,4-dimethyl-1,3,2-dioxaborinane and its oxonium ions was studied. It was shown that the potential energy surface of the studied molecules has minima corresponding to equatorial (main minimum) and axial sofa forms and maxima corresponding to equatorial and axial conformations of 2,5-twist forms. Calculated values of the barriers of internal rotation of methyl group at the ring C⁴ atom were found. It was also established that the heat of protonation of the cyclic boric ester was smaller than of the non-boric analog, cis-2,4-dimethyl-1,3-dioxane, owing to decrease in basicity of the oxygen atoms in the cyclic boric ester due to partial double bond character of B-O bond.     

Structure of the CCl3CCl=NCH2C6H5 molecule and reorientations of its CCl3 group, according to ab initio calculations

The optimal geometry of the isolated CCl₃CCl=NCH₂C₆H₅ molecule and the intramolecular barrier to reorientations of its trichloromethyl group are calculated by the RHF/6-31G* and B3LYP/6-31G* methods. The barrier found (14.1 kJ mol^?1) is compared to that determined previously by ³⁵Cl NQR for a crystal of this compound, which allows estimation of the contribution of intermolecular interactions to braking of this motion of the CCl₃ group. The structural features of the molecule of this compound are consistently manifested in quantum-chemical calculations and NQR spectra.     

Ab initio and MNDO Calculations of Cyanuric Chloride,its 35Cl NQR Frequency and Asymmetry Parameter of the EFG at the 35Cl Nuclei

Ab initio molecular orbital calculations of the (CNCl)₃ (cyanuric chloride; 2,4,6-trichloro-1,3,5-triazine) molecule were performed at the RHF/6–31G* level. The ³⁵Cl NQR frequency and asymmetry parameter of the EFG at the ³⁵Cl nucleus were calculated from the total populations of the Cl atom valence p-orbitals and their components. The ³⁵Cl NQR frequency and asymmetry parameter which are determined for (CNCl)₃ based on these components agree well with the corresponding experimental values and demonstrate the importance of including the less diffuse components of the p-orbitals.     

Quantum chemical study of the appearance of the “α-effect” in35Cl NQR spectra of chloromethylsilanes

We consider the connection between the electron distribution in ClCH₂MX₁X₂X₃ molecules (M = C, Si) calculated by the CNDO/2 method and the experimental³⁵Cl NQR frequencies. We show that the ratio of the NQR frequencies for chloromethylsilanes and their organic analogs can be explained on the basis of ideas concerning the totality of induction and conjugation effects influencing the population of the orbital of the chlorine atom which participates in formation of the C-Cl bond.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 241–244, March–April, 1990.     

Characteristic features of interaction between atoms in chloro-substituted 1,4-dioxane fromab initio calculations

Ab initio calculations in a split-valence shell 6-31G(d) basis for the 2-chloro-1,4-dioxane (with axial and equatorial Cl atom) and 2,3-cis-dichloro-1,4-dioxane molecules with full optimization of their geometry were performed. The major contribution to the lowering of the NQR frequencies of the axial Cl atoms compared with the equatorial Cl atoms comes from the higher p-electron population of the former in these molecules. The populations of the orbitals for the unshared electron pairs of the axial and equatorial Cl atoms are identical in these molecules. But these orbitals are polarized differently, which also has some effect on the ratio of the NQR frequencies of these atoms. The differences in the electron populations of the axial and equatorial Cl atoms for the studied molecules are due to the asymmetry of the electron distribution in the Cl atoms geminal to them, which is responsible for the different polarization of the valence p-orbitals of the axial and equatorial Cl atoms.Institute of Technical Chemistry, Urals Branch, Russian Academy of Sciences, Perm' 614000, Russia; e-mail: chemist@mail.psu.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1485–1490, November, 1999.     

Structure and rotational isomerism of chloroacetyl chloride molecules

The structure of chloroacetyl chloroide (CH₂ClCOCl) molecule in different conformations arising from rotation of the CH₂Cl group about the C-C bond was determined by the Hartree-Fock RHF/6-31G(d) quantum-chemical calculations. The energy difference between the two stable rotamers was estimated at 5.9 kJ mol^?1, and barriers to intramolecular reorientations of the CH₂Cl group were calculated.