The effect of the valent state of the heteroatom on the spectrochemical evidence of conjugation in allyl compounds of sulfur and phosphorus

The effect of valency of the heteroatom on the spectrochemical evidence of the conjugation in allyl derivatives of S^II,VI and P^III,IV was studied by quantum chemical methods. The geometric and electronic structures of thetrans- andgauche-conformers, including those for allyl compounds of P^V with equatorial or axial P-C bonds, were calculated. According to the calculations, inversion of the higher occupied molecular orbitals (MO) and the convergence of their energies resulting from the replacement of weak n,-conjugation by strong ,-conjugation should occur on going from S^II and P^III to S^VI and P^V. Increasing the interaction between the higher occupied MO of the fragments in the non-planar conformation of the molecule causes strengthening of the spectral evidence of conjugation: a decrease in the first ionization potential and a bathochromic shift of the long-wavelength absorption band in the electronic spectrum. The increased relative stability of thegauche-conformers of allyl compounds of hypervalent elements was explained by the through-space interaction between the vacant d-orbitals of the S^VI and P^V atoms and the -orbital of the C=C bond. Charge transfer between the molecular fragments makes the major contribution to the energy of conjugation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 43–47, January, 1995.The work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 93-03-5566).     

Bond orders and valences in the SCF theory: a comment

The calculation of bond order and valence indices for ab initio and semi-empirical wave functions is discussed by emphasizing their relations to the exchange part of the second order density matrix. Comments are also given on a recent work of Gopinathan and Jug, as well as propositions made to avoid ambiguity in the nomenclature.     

Quantum-chemical investigation of the dependence of pK a on the calculated energy of proton removal for certain derivatives of indole and phenol

The total energies of derivatives of N-hydroxyindole, indole, and phenol, and of their corresponding anions have been estimated with the aid of ab initio calculations on the 3-21G basis. The energies of proton removal were calculated from the difference in total energies of the appropriate anions and molecules. By comparing the calculated energies of proton removal with experimental values of pK_a (acidity characteristic) a practically linear dependence was shown for the acidity characteristic on the energy of proton removal for the series of compounds investigated. An empirical formula has been proposed expressing the dependence of pK_a on the energy of proton removal, which makes it possible to predict pK_a in this series by carrying out calculations of the energy of proton removal (transfer). __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 47–50, January, 2006.     

[M(Im)2X2]型配合物的Far-IR和Raman光谱的理论研究

本文用从头计算RHF和密度泛函B3LYP方法以及LanL2DZ，SDD和6-31G(d)基组计算了配合物M(Im)₂X₂ (Im=imidazole；M=Zn(Ⅱ)，Pd(Ⅱ)，Pt(Ⅱ)；X=F，Cl，Br，I)的几何构型以及Far-IR和Raman振动频率。计算结果表明，对Zn(Ⅱ)配合物而言,B3LYP/6-31G(d)方法得到的几何参数与实验值吻合得最好，B3LYP/SDD次之。在计算Far-IR和Raman振动频率时，发现采用6-31G(d)基组，两种方法计算的结果差别不大。对LanL2DZ和SDD基组而言，对计算结果影响较大的是理论方法，基组影响甚微，个别的振动频率基组影响较大，相比较而言，SDD基组得到的结果更好一些。本文所使用的两种计算方法都能得到与实验值比较吻合的结果，而用从头计算RHF方法计算的结果与实验值更接近一些。在此基础上，预测了Pd(Ⅱ)和Pt(Ⅱ)配合物的Far-IR和Raman振动频率。     

Conformational Study of Naringenin in the Isolated and Solvated States by Semiempirical and Ab Initio Methods

Naringenin is a natural widespread flavanone occurring in different foodstuffs that presents several important biological activities. Although its properties are well documented, its mechanisms of action are still controversial. The present article reports a conformational analysis of naringenin, using the semiempirical AM1 and ab initio methods, at the Hartree–Fock level of theory. The 3-21G, 3-21G*, 6-31G, and 6-31G** basis sets were used. The electron correlation effects were included through the Møller–Plesset second-order perturbation theory. The solvation of naringenin has been investigated through the standard SCRF, the supermolecule (SM), and the combined SM/SCRF models. The results have shown that there are two degenerate forms of naringenin, differing mainly by the orientation of a hydroxyl group (C4—OH). The energy barrier for the interconversion between them is ca. 6 kcal.mol^–1, suggesting some conjugation between the -system of the aromatic B ring and the hydroxyl group (C4—OH).     

Kinetic calculation for the reaction of H with Si2H6 using the variational transition state theory

The reaction of disilane with atomic hydrogen has been studied. This reaction involves both substitution and abstraction. Calculations show that the hydrogen abstraction is the strongest competing channel. The canonical variational transition state theory with a small curvature tunneling correction (SCT) has been used for the kinetic calculation. The theoretical results are in good agreement with the available experimental data. Comparing the reactions of atomic hydrogen with disilane and silane, it can be seen that the reactivity of the Si-H bond is higher in Si₂H₆ than that in SiH₄.     

Theoretical investigation on regioselectivity of aromatic ketones in the addition with olefin catalyzed by RuH2(CO)(PPh3)3

Ab initio method is employed to study the structures of twelve aromatic ketones at HF/3-21G, HF/6-31G and HF/6-31G* levels, respectively. A theoretical analysis is also carried out to study the regioselectivity and reactivity of aromatic ketones in the addition with olefin catalyzed by RuH₂(CO)(PPh₃)₃. The results indicate that a U shape LUMO conjugation of aromatic ketones in a plane plays an important role in regioselectivity on the cleavage of β C-H bond and is a necessary factor to success of addition with olefin, and that steric effect is an indispensable factor in forming additional ortho-product. Meanwhile, electronic effect may influence the rate of addition for the structures alike which only have different replacements in the same site of aromatic ring, such as furan, thiophene and pyrole. A possible catalytic reaction mechanism is proposed that the addition of C-H bond may be carried out by a coordination of aromatic ketones with Ru complex.     

Desolvation effects on the dissociation energy of diatomic molecules:Ab initio study of the dissociation of Li-F in polar media

Summary The potential curve of the ground state dissociation of Li-F in water has been studied by a combination of a standardab initio Hartree-Fock procedure and a perturbative reaction field approach. The electrostatic solute-solvent interaction is accounted for by the generalized Born formalism introduced through a perturbation approach. The calculations were carried out at a 6–311+G* basis set level. Diffuse functions ofs symmetry were included to model a desolvation potential. A double well potential curve was obtained for the dissociation of this molecule in the presence of a highly polarizable medium. The first minimum, corresponding to an ion pair, electrostatically bound, is found at aR(Li-F)<6.0 Å distance. As the two ions come together, a desolvation barrier of about 30 kcal/mol is to be overcome before the formation of the neutral Li-F at 1.56 Å. The barrier to ionization towards the ion pair is calculated to be about 14 kcal/mol. The dissociation of the ion pair towards the free ions is discussed in terms of the electrostatic solvation entropy changes.Contribution No 6 from Centro de Mecánica Cuantica Aplicada (CMCA)     

A General Equation Holds for the Geometry of Hydrogen Bonds with O and N Acceptors

A unique equation able to correlate two geometrical parameters in hydrogen-bonded (HB) systems, the X—H covalent bond distance of the donor and the HY distance of the acceptor, has been devised. The equation is able to fit high-quality crystallographic data of different HB donors and several nitrogen and oxygen acceptors.     

On the molecular electrostatic potentials obtained with CNDO and INDO wave functions

Molecular electrostatic potentials computed with CNDO/2 and INDO wave functions are shown to present systematic differences with respect to ab initio potentials in the case of out-of-plane potentials and in-plane vicinal hetero atoms in planar hetero molecules.     

Ab initio calculations of chloride complexes of Au, Hg, Tl, Pb, and Bi in anomalous oxidation states (2S1/2 electron state)

Ab initio calculations of chloride complexes of Au, Hg, Tl, Pb, and Bi in anomalous oxidation states (²S_1/2 electron state) were carried out by the Becke-Lee-Yang-Parr density functional method using the Dunning-Hay LanL2DZ basis set. Optimum geometric parameters and electronic characteristics of MCl _n (H₂O) _m ⁿ (n=1–4 andm=0,4,5) complexes were determined. In each of the considered series the spin, population on the central metal atom decreases as its atomic number increases. The energy of transition of the unpaired electron to the lowest unoccupied MO decreases in the same order. The unpaired electron occupies an orbital that is mostly a linear combination of the s-orbital of the metal atom and the p-orbital of the Cl atom (the antibonding σ-orbital of the M−Cl bond). Distinctions in the changes in spectral properties of aquacomplexes and chloride complexes in isoelectronic series, observed as the degree of oxidation of the metal atom increases, were explained. The results of calculations are in agreement with the experimental data obtained by ESR and optical spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1049–1055, June, 1999.     

Ab initio study of the ground state and conformational stability of peroxyacetyl nitrate in internal rotation about the peroxide bond

The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998.     

二苄基锡二(2-哇啉甲酸)酯的合成、结构及量子化学研究

The novel dibenzyltin bis(2-quininate) has been synthesized. The crystal structure of the complex was determined by X-ray diffraction. The crystal belongs to monoclinic space group P2₁/c with a=1.840 05(14) nm, b=2.353 66(18) nm, c=2.044 31(16) nm, β=99.3130(10)°, V=8.736 9(12) nm³, Z=4, D_c=1.507 g·cm^-3, μ(Mo Kα)=9.21 cm^-1, F(000)=4 016, R₁=0.041 4, wR=0.082 1. In this compound, the tin atom rendered six-coordinated in a distorted octahedron geometry. The study on title complex has been performed, with quantum chemistry calculation by means of G98W package and taking Lanl2dz basis set. The stabilities of the complex, the orbital energies and composition characteristics of some frontier molecular orbitals have been investigated. CCDC: 609510.     

Orientation of molecules by magnetic field as a new source of information on their structures

A complex procedure for quantitative allowance for small but significant effects of molecular orientation by strong static magnetic fields was elaborated. A series of high-resolution ¹H NMR spectra of 1,2,3-trichloronaphthalene recorded at magnetic field strength varied over a wide range was analyzed in the framework of a unified approach with high accuracy. The spin-spin coupling constants and the dipole-dipole coupling constants for all pairs of ¹H nuclei and the anisotropy and rhombicity parameters of the magnetic susceptibility tensor of the molecule were determined. Ab initio CSGT/RHF quantum chemical calculations of this property using a wide range of conventional diffuse and polarization basis set functions were carried out. Augmentation of the basis set with polarization functions affects the values of the calculated parameters to a lesser extent compared to augmentation with diffuse functions. The results of calculations using the 6-311G(df) and 6-311++G(df) basis sets are in good agreement with the experimental values of the magnetic susceptibility anisotropy for 1,2,3-trichloronaphthalene. The advantages of the method proposed and specific features of the effects of orientation by magnetic field as a new source of information on the structure of molecules in solution are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1309–1317, August, 2006.     

HeI photoelectron spectroscopic (PES) and quantum chemistry study on the dimeric compound of 2(5H) furanone

The He1 photoelectron (PE) spectra of both 2(5H) furanone and itstrans-chair-dimeric-compound (t-c-DFN) are reported. The assignment of the PES bands is made on the basis of band shapes, the PES results of the molecules which have the similar atomic groups, and the restricted Hartree-Fock (RHF) calculations for the molecules studied. From the results of both PES experimental and theoretical calculations, it is proved that the ionization potential (IPS) of the HOMO for the dimeric-compound is lower than that of the HOMO for the monomer. And the total energy computed for thet-c-DFN is the lowest in the four possible configurations of dimeric-compounds of 2(5H) furanone. Therefore the synthesis oft-c-DFN is also the easiest. Project supported by the National Natural Science Foundation of China.     

Theoretical study of the intermolecular hydrogen bond interaction for furan-HCl and furan-CHCl<Subscript>3</Subscript> complexes

The nature of the intermolecular hydrogen bond for the furan-HCl and furan-CHCI₃ complexes has been studied using ab initio calculations with MP2 level of theory. The new hydrogen bond type of C(CI)-H...O and π interactions are studied also. It is shown that, for the optimized geometries of furan-CHCI₃, C-H bond lengths contract and vibrational frequencies are blue-shifted, while for the furan-HCl complex, H-CI bond lengths elongate and vibrational frequencies are red-shifted. In addition, the NBO analysis indicates that, for the furan-CHCI₃ complex, the charge transfers from the lone pair of the proton acceptor to both σ *(CH) antibonding MO and lone pairs of CI atom.     

Dipole moments of aryl cis - and trans -styryl sulphides and sulphones

The dipole moments of thirteen aryl styryl sulphides and eleven aryl styryl sulphones have been determined. Among them are eightcis-trans isomeric pairs, four sulphides and four sulphones. The styryl group is found to conjugate with the sulphide function as an electron-withdrawing group. The angles which the styrylthio and styrylsulphonyl groups make with their axes of rotation are calculated. The observed dipole moments of the sulphides and sulphones are compared with the moments calculated by the vector addition of group moments. The dipole moments ofcis aryl styryl sulphides and sulphones are found to be generally lower than those of theirtrans isomers. An explanation is offered attributing the cause to sterically enhanced styryl-sulphur conjugation in thecis isomers.     

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.     

X-ray photoelectron and voltammetry studies of the charged state of the metal atom in nickel(II) chelate complexes with ligands containing CS 2? and PS 2? groups and in their mixed-ligand complexes

X-ray photoelectron and voltammetry studies of the charged state of the metal atom in nickel(II) chelate complexes with ligands containing CS ₂ ⁻ and PS ₂ ⁻ groups and in heteroligand complexes on their basis were carried out. It is shown that the degree of formal oxidation of the nickel atom in the complexes corresponds to Ni(II). In the case of heteroligand complexes, addition of nitrogen heterocycles causes an increase in the electron density on the atoms of the coordination center. Theoretical data obtained in ab initio quantum chemical model calculations correlate with the experimental results. Original Russian Text Copyright ? 2005 by L. N. Mazalov, S. V. Trubina, I. M. Oglezneva, N. A. Kryuchkova, O. V. Tarasenko, V. L. Varand, T. E. Kokina, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 554–557, May–June, 2005.