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.     

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.     

Ab initio calculations ofo- andm-Cl2C6H4 molecules and their35CI NQR parameters

The MNDO andab initio (Hartree—Fock method, split 6-31G^* basis set, full optimization of geometry) calculations for theo- andm-dichlorobenzene molecules have been performed. The populations of the valent p-orbitals of the carbon and chlorine atoms have been analyzed. Estimations of the³⁵Cl NQR frequencies and the asymmetry parameters of the electric field gradient at the³⁵CI nuclei have been made. It was confirmed that these values are not determined by the contribution of the whole valent p-shell, but only by its less diffuse component.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2180–2183, September, 1996.     

Ab initio calculations ofp-Cl2C6H4 molecule and its35Cl NQR parameters

Ab initio calculations ofp-dichlorobenzene molecule were carried out using the Hartree-Fock method in the 6–31 G* valence-split basis set. The molecule was also calculated by the MNDO method in the valence sp-basis set for comparison. The populations of the valent p-orbitals of the C and CI atoms were analyzed. The optimized geometry of the molecule as well as its³⁵Cl NQR frequency and the asymmetry parameter of the electric field gradient at the³⁵CI nuclei calculated using the populations of the less diffuse components of the valent p-orbitals of the Cl atoms are in agreement with the corresponding experimental values for the -modification of 1,4-Cl₂C₆H₄.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2177–2179, September, 1996.     

Stereoelectronic structure of MCl4-benzoyl chloride (M=Si,Ge, Sn) systems resulting from ab initio calculations and NQR 35Cl

Results of quantum-chemical calculations of MCl₄–C₆H₅COCl (M=Si, Ge, Sn) systems of 1?:?1 composition using RHF/3-21?G* and MP2/3-21?G* levels as well as those of 1?:?2 composition using the RHF/3-21?G* level have been represented. MCl₄?←?C₆H₅COCl complexes of 1?:?1 composition are energetically more advantageous. They are formed in solid state provided that the M···O distance in individual systems is considerably less than the sum of van der Waals radii of M and O and their total energies are appreciably less than the sum of total energies of components. These conditions are realized only for M=Sn. In systems of 1?:?2 compositions, calculated M···O distances are practically equal to the sum of covalent radii of M and O. Nonetheless, complexes with such composition are not formed in solid state. Total energy of the system which is lower than the sum of its components’ energies is not an indispensable condition for complex formation. The ³⁵Cl nuclear quadrupole resonance (NQR) frequencies and asymmetry parameters of the electric field gradient at the ³⁵Cl nuclei have been evaluated using the results of ab initio calculations.     

Ab initio calculations of of pyridine and its 2- and 3-chloroderivatives

Ab initio calculations of the C₅H₅N, 2-. and 3-ClC₅H₄N molecules by the RHF method in the valence split 6-31G^* basis set with full optimization of the geometry have been carried out. The alternation of the charges on the atoms of the pyridine ring and of the populations of their p _x -orbitals is in agreement with the noninductive through -the-field interaction of the geminal atoms. The³⁵Cl NQR frequencies and the electric field gradient asymmetry parameters at the³⁵Cl nuclei in 2- and 3-CIC₅H₄N were estimated using the populations of the valentp-orbitals of the Cl atoms and their components. The³⁵Cl NQR frequency for the first compound is lower than that for the second one, mainly due to the higher p-electron population of its Cl atom.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2641–2644, November, 1996.     

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.     

Ab initio calculation of 4-ClC6H4CH2Cl and peculiarities of electron density distribution in this molecule

Ab initio calculation of the 4-ClC₆H₄CH₂Cl molecule was performed by the restricted Hartree-Fock method in the split valence 6–31 G* basis set with complete optimization of its geometry. Populations of p-orbitals of atoms of this molecule were analyzed.³⁵Cl NQR frequencies and asymmetry parameters of the electric field gradient on³⁵Cl nuclei were estimated on the basis of the populations of valent p-orbitals of CI atoms and their components. Good conformity with the experimental values was obtained when only less diffuse components of p-orbitals were used in calculations of populations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 823–826, April, 1996.