35Cl NQR spectra, structure, and mutual influence of substituents in the series of chlorine-containing organic compounds of pentavalent phosphorus

Regularities of transmission of the effect of equatorial and axial substituents were established for a number of chlorine-containing organic compounds of pentatalent phosphorus using³⁵Cl NQR spectra. The field constants of³⁵Cl NQR frequencies of the chlorine atoms participating in the P−Cl bond were estimated for a series of tetrahedral phosphorus ions. The³⁵Cl NQR frequencies of chlorine atoms in tetracoordinated ions of pentavalent phosphorus and in analogous isoelectronic silicon compounds are related by a linear dependence. Deceased Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 915–922, May, 1999.     

Features of the molecular structure of compounds of (Cl3PNAr)2 series (Ar = C6H4Z, Z = H, Cl) by quantum-chemical calculations and the data of 35Cl nuclear quadrupole resonance

A series of dimeric molecules (Cl₃PNAr)₂ where Ar = C₆H₄Z, Z = H or Cl in 2–4 positions, was calculated by the RHF/6-31G* method with the full geometry optimization. A specific nature of the intramolecular steric orientation of aryl groups was revealed, therewith in the case Ar = C₆H₄Cl-2 short nonvalent contacts were founf between the ortho-chlorine atom and PCl₃ group manifested in the peculiarity of geometric parameters and NQR spectroscopy data of this compound. The correlation of the ³⁵Cl NQR frequencies of P-Cl bonds with the values of the charges on the chlorine atoms obtained by quantum-chemical calculations of the molecules was analyzed.     

Quantum chemical calculations and35Cl NQR study of the molecular structure of trichloroacetyl halides and trichloroacetaldehyde

An optimal geometry of CCl₃C(O) X molecules (X=H, F, Cl, Br, and I) is determined by the MNDO quantum chemical method. According to the results of calculations, the molecules in the free state have an eclipsed conformation with a syn-peri-planar position of the oxygen atom and one of the chlorine atoms of the trichloromethyl group. However, as follows from the³⁵Cl NQR spectra at different temperatures, in the crystal state of CCl₃C(O)X this conformation is distorted under the influence of intermolecular interactions due to the torsional rotation of the CCl₃ group around the C-C bond. Indicatory potentialities of the NQR method with respect to the structural features that are due to crystallographic effects are discussed. Perm State University. Translated fromZhurnal Strukturmoi Khimii, Vol. 37, No. 3, pp. 494–500, May-June, 1996.     

Thermally activated intramolecular motion in the crystalline complex SbCl3 · C6H4(NO2)2-m

Temperature dependences of the ³⁵Cl and ¹²¹Sb NQR frequencies and the spin-lattice relaxation times in the molecular complex of antimony trichloride with meta-dinitrobenzene were investigated. These dependences for ³⁵Cl nuclei suggest a thermoactivated motion of chlorine atoms with the activation energy E _a = 50 kJ/mol in the crystal. The data obtained were used for determination of the molecular structure of the complex. Some features of the intramolecular motion in SbCl₃ complexes of the vπ and vn types were discussed. The ¹²¹Sb NQR data revealed no thermoactivated motion of the ligands bound to the Sb atom.     

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.     

On the estimation of the field constant of 35Cl nuclear quadrupole resonance frequency in the series of [R1R2R3AsCl]+M? compounds

The field constant of the NQR frequency of a chlorine atom (³⁵Cl) in a series of arsenic derivatives [R¹R²R³AsCl]⁺M⁻ was estimated from correlations. The field frequency is ∼41.5±3.5 Hz cm kV⁻¹, which is nearly twice as much as that in analogous phosphorus compounds. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1758–1760, August, 2005.     

Sigmatropic mechanism of the chlorotropic isomerization of phosphazopentachloroethane

The sigmatropic and dissociative-recombination mechanisms of the chlorotropic isomerization of benzodioxachlorophosphazopentachloroethane and its 1:2 solvate with chloroform have been studied by the MNDO-PM3 method in the supermolecular approximation. It is observed that the thermodynamically more stable chlorotropic isomer corresponds to the phosphorane structure with axial-equatorial disposition of two chlorine atoms and the two oxygen atoms in the dioxaphosphole ring, in complete agreement with literature data on teh³⁵Cl NQR spectrum. It is shown that the most likely pathway for phosphorus-carbon chlorotropic rearrangement for both phosphazopentachloroethane and its solvate with two molecules of chloroform is the sigmatropic route. Institute of Bioorganic and Oil Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 02094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 177–181, May–June, 2000.     

Atomic ordering in CuGeO3 during the spin-Peierls transition: Calculation of63Cu NQR frequencies

The X_α discrete variation (X_α-DV) method is used to calculate the electronic structures of the clusters modeling the spin-Peierls transition in CuGeO₃. The⁶³Cu NQR frequencies of two centers that fall within the simulated supercell are calculated. It is shown that the nature of the forbidden gap and the⁶³Cu NQR spectral parameters depend on the motion of copper atoms in the chains. Some assumptions are made to explain the fact that dimerization in chains of Cu atoms is experimentally unobservable. Translated from Zhurnal Strukturnoi Khimii, Vol. 38, No. 1, pp. 43–50, January–February, 1997.     

New Method for calculating effective charges on atoms in molecules, clusters, and solids

A procedure for calculating effective charges on atoms in an arbitrary polyatomic system has been developed on the basis of the one-electron DV cluster method. Effective charges are calculated as three-dimensional integrals of electron density over the space around atomic nuclei in the object under investigation. An original procedure is suggested to assign the charge density to a particular center at every point of space. Translated fromZhurnal Struktumoi Khimii, vol. 39, no. 6, pp. 1134–1140, November–December, 1998.     

35Cl, 93Nb, 181Ta,and 121Sb NQR in Cl5MV · OPCl3 (MV = Nb,Ta, Sb,or P) Complexes

The behavior of ³⁵Cl NQR spectra in Cl₅M · OPCl₃ complexes is affected by the nature of the metal center and the distortion of its surrounding geometry. In all cases considered, the ³⁵Cl NQR frequencies in the OPCl₃ fragment shift toward higher frequencies upon complex formation, whereas the frequencies of axial chlorine atoms in the Cl₅M group in the phosphorus and antimony complexes lie below those for the equatorial atoms, and in the niobium and tantalum complexes, the frequencies of the axial atoms are higher than those of the equatorial ones.     

Studies of the substituent effect in aromatic systems by 35 Cl-NQR. Chloroacetanilides ClxC6H5−x NHCOCH3−y Cly

The ³⁵Cl-NQR spectra of 45 chlorosubsitituted acetanilides, Cl_xC₆H_5?xNHCOCH_3?yCl_y, were investigated and the temperature dependence of some spectra, especially of monochloroacetic acid derivatives, was measured. A preliminary assignment of the NQR frequencies is given. A correlation between NQR frequencies and substituent parameters permits the study of the substituent effect of the acetamido group, ? NHCOCH_3?yCl_y. The chloro-substitution in the side chain of the acetanilides seems to have no noticeable influence on the ³⁵Cl-NQR frequencies of the chlorine atoms at the benzene ring. The NQR frequencies of the chlorine atoms in the chloroacetamido group are, on the other hand, insensitive to substitutions at the benzene nucleus. The possibility of steric influences on the NQR spectrum of ortho-chloro-substituted acetanilides is discussed. The investigation further confirms that a crystal field effect of about ±500 kHz must be considered in the interpretation of NQR spectra of chlorobenzene derivatives.     

35Cl NQR spectra of osmium and iridium chlorochalcogen complexes

Conclusions A study was carried out on the NQR spectra of the chlorine atoms in Os(IV) and Ir(III) complexes with sulfur, selenium, and tellurium chlorides as ligands. The ECl₃ group coordinates as the ligand in the osmium compounds studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1409–1411, June, 1986.     

Electronic structure analysis of 4-chlorophenylisoxazoles and 4-chloroisoxazolines by35Cl NQR spectra and quantum chemical calculations

Electronic structure of substituted phenylisoxazoles and substituted isoxazolines is examined by³⁵Cl NQR and MINDO/3 calculations. It is shown that the chlorine atom in the 4-position of the isoxazole ring serves to transmit the influence from the phenyl ring in the 3-position to that in the 5-position. The influence is transferred via both the σ- and π-bond systems. Tomsk State Pedagogical Institute. Institute of Chemistry, A. Mitskevich University. Institute of Biophysics, Health Ministry of Russia. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 61–68, March–April, 1994. Translated by L. Smolina     

Supported complexes of cupric chloride with DMF as catalysts in the reaction of CCl4 withn-decane

The complex of cupric chloride with DMF immobilized on the surface of silica gel exhibits high catalytic activity in the reaction of tetrachloromethane withn-decane. The fact that the reaction is inhibited by phenols and oxygen implies that it occurs by a radical mechanism. The immobilized catalyst that contains copper atoms connected through chlorine bridges and organic donor ligands is the most effective. Presented at the First Moscow Workshop on Highly Organized Catalytic Systems. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1835–1838, October, 1997.     

Evaluation of the reactivity of new activated difluoroaromatic compounds

To evaluate the reactivity of new difluroroaromatic compounds in nucleophilic substitution, the positive charges on carbon atoms of C−F bonds were calculated using the quantum-chemical semiempirical PM3 method. A correlation between the charges calculated and the chemical shifts in the¹⁹F NMR spectra was established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 623–625, April, 1998.     

Cl35 nuclear quadrupole resonance spectra of chloro-substituted 6-pyridazone derivatives

The effect of substituents in the pyridazone ring (including the carbonyl oxygen atom) on the chlorine atoms in the 3,4, or 5 positions was investigated on the basis of data from the Cl³⁵ nuclear quadrupole resonance (NQR) spectra of chloro-substituted 6-pyridazones. The NQR frequencies of 1-phenyl-4,5-dichloro-6-pyridazone were compared with the reactivities of chlorine atoms in this compound in nucleophilic substitution reactions.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.3, pp. 392–395, March, 1976.     

Electronic and Spatial Structure of Piperidine and Its Substituted Derivatives from the Results of ab initio Calculations

The results of non empirical quantum-chemical calculations using the RHF/6-31G(d) and MP2/6-31G(d) methods do not agree with proposals for the axial position of the H atom on the N atom in the piperidine molecule. According to RHF/6-31G(d) calculations for the N-methylpiperidine molecule and its chloro-substituted derivatives an equatorially placed methyl group is energetically more favored than an axial. The axial C-Cl and C-H bonds in these molecules are longer than the equatorial. The ³⁵ Cl NQR frequencies for the axial Cl atoms are lower than the equatorial. The ³⁵ Cl NQR frequency of the axial chlorine atom in 2-chloro-1-methylpiperidine is anomalously low. This is chiefly due to the high population density of its p σ-orbital and this is a result of the polarization of the C-Cl bond via the N atom unshared electron pair directly through the field. The effect of a similar unshared electron pair on the parameters of the C-Cl bond in the ClCH₂NH₂ molecule has been studied by the RHF/6-31(g) method for different angles of rotation of the ClCH₂ group around the C-N bond. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1044–1052, July, 2005.     

Quantum chemical prediction of the 13C NMR shifts in alkyl and chlorocorannulenes: correction of chlorine effects

Prediction of the ¹³C NMR shifts of sym-pentachlorocorannulene and decachlorocorannulene provided impetus for the development of a correction scheme based on a regression of experimental and quantum chemical data. A training set of 15 compounds (18 carbon signals) comprising carbons atoms bearing 1–4 chlorine atoms leads to an estimated error per chlorine atom of about 10–12 ppm. Specifically, linear regression of the data obtained at B3LYP/cc-pVDZ leads to y = −3.77 + 13.11x, with R = 0.982. Ultimately, experiment and theory converge for sym-pentachlorocorannulene and decachlorocorannulene, the former by correction of the theory, the latter by collecting the proper experimental data. Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue.     

A quantum-chemical study of 1,2,3,4,5,6,7,8-octaazanaphthalene and itsN-oxides

Calculations of hypothetical molecules of octaazanaphthalene and itsN-oxides were performed by the MNDO method with full geometry optimization. Probable decomposition reactions of these compounds were considered. Compounds with more pronounced alternation of charges on adjacent atoms were shown to be more thermodynamically favorable and thermally stable. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 879–881, May, 1999.     

On determination of the strength of local electric fields at the bromine atoms in the series of compounds BrCH2R by79Br NQR spectroscopy

The values of changes in the strength of local electric fields at the bromine atoms for a series of compounds BrCH₂R were determined from a hyperbolic equation relating the⁷⁹Br NQR frequencies to their field constants. The totalities of electron-acceptor and electrodonor substituents R are described by equations of the same type differing in their parameters. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1150–1154, June, 1998.