NMR spectroscopic study of the effects of conjugation

Conclusions We have examined the¹³C NMR spectra of para- and meta-substituted alkylthiobenzenes. Steric disruption of the p, -conjugation of sulfur with the aromatic fragment on increase in the size of the alkyl substituents is typical of all the series. The degree of p,-conjugation and the molecular conformation also depend on the electronic effects of the para and meta substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1525–1531, July, 1981.     

Pyrroles from ketoximes and acetylene

The ¹³C NMR spectra of eight 2-alkyl- and 2,3-dialkyl-1-vinylpyrroles were studied. The ¹³C chemical shifts of all of the carbon atoms of the ring and the vinyl group depend substantially on the position and structure of the alkyl substituent. As the branched character of the alkyl group in the 2 position increases, the signal of the -carbon atom of the vinyl group is shifted to weak field due to weakening of the p- conjugation in the N-vinyl group because of disruption of its coplanarity with the pyrrole ring. The conjugation between the double bond and the pyrrole system involves competition for possession of the p electrons of the nitrogen atom.See [16] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 350–354, March, 1978.     

An <Emphasis Type="Italic">ab initio</Emphasis> quantum-chemical study of the compounds HC≡CXCH<Subscript>3</Subscript> (X = O,S, Se)

The compounds HCCXMe (X = O, S, Se) were studied by the MP2(full)/6-31G* ab initio method using the method of natural bond orbitals. The parameters of the molecular geometry were obtained. The electron density distribution in these compounds is determined to a greater extent by the electronegativity of atoms X, than by conjugation of the lone electron pairs of the heteroatoms with the triple bond.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1823–1827.Original Russian Text Copyright © 2004 by Bzhezovskii, Kapustin, Chura, Shermolovich.This revised version was published online in April 2005 with a corrected cover date.     

Steric and Electronic Structure of Selenoanisole: A Quantum-Chemical Study

The potential functions of internal rotation around the C_sp2-Se bond in selenoanisole were ob- tained by quantum-chemical calculations in the approximations HF/3-21G(d), HF/6-31G(d), MP2(f)/6-31G(d), and B3LYP/6-31G(d). The calculations were performed in the range of variation of the torsion angle (between the planes of the benzene ring and C_sp2-Se-C_sp3 bonds) from 0° to 90° with 15° step. The energy minimum is in the region of the orthogonal conformation ( 90°), and the energy maximum, in the region of the planar form ( 0°). The rotation barriers (kJ mol^{- 1}) are as follows: HF/3-21G(d), 9.20; HF/6-31G(d), 13.13; MP2(f)/6-31G(d), 10.25; and B3LYP/6-31G(d), 6.41. The geometric parameters, Koopmans ionization potentials, and dipole moments are given. The energies, degrees of hybridization, populations of the lone electron pairs of Se, energies of their interaction with the antibonding * orbitals of the benzene ring, and electron density distributions were determined in terms of the natural bond orbital approach.     

Intramolecular Interactions in Anisole,Thioanisole, and Selenoanisole. Application of Natural Bond Orbitals Method

Calculations of molecules PhXMe (X = O, S, Se) in MP2(f)/6-31G(d) approximation were performed. The stationary points on the potential energy surface were determined and identified. The anisole molecule is planar with a barrier to rotation H 7.78 kJ mol^-1. In thioanisole and selenoanisole (H 3.08 and 10.25 kJ mol^-1 respectively) the energy minimum corresponds to an orthogonal form. Analysis of relation between intramolecular interactions and conformational structure of the molecules in question was performed by the method of natural bond orbitals. In X atoms one lone electron pair is a hybrid orbital with the following fraction of s-component: 38-45% (O), 66-68% (S), and 73-74% (Se). The second lone electron pair is virtually pure pz-AO.     

An <Emphasis Type="Italic">ab initio </Emphasis> Quantum-Chemical Study of C<Subscript>6</Subscript>H<Subscript>5</Subscript>S(O)CH<Subscript>3</Subscript> and C<Subscript>6</Subscript>H<Subscript>5</Subscript>S(O)CF<Subscript>3</Subscript>

The potential functions of internal rotation around the C -S bond in the C₆H₅S(O)CH₃ and C₆H₅S(O)CF₃ molecules were obtained by ab initio MP2(full)/6-31+G* calculations. The stationary points were identified by solving the vibrational problems. The structures in which the plane of the C -S-C bonds is approximately perpendicular to the benzene ring plane correspond to the energy minimum. The barriers to rotation around the C -S bond, corrected for the zero-point vibration energy, are 21.29 [C₆H₅S(O)CH₃] and 28.98 [C₆H₅S(O)CF₃] kJ mol⁻¹. The bond angles (deg) are as follows: 95.7 (CSC), 107.1 (C SO), 106.3 (C SO) in C₆H₅S(O)CH₃; 93.5 (CSC), 108.2 (C SO), 105.2 (C SO) in C₆H₅S(O)CF₃. The bond lengths are as follows (Å): 1.520 (S=O), 1.804 (C -S), 1.810 (C -S) in C₆H₅S(O)CH₃; 1.507 (S=O), 1.799 (C -S), 1.870 (C -S) in C₆H₅S(O)CF₃. According to the results of NBO calculations, the formally double S=O bond consists of a strongly polarized covalent σ bond (S→O) and an almost ionic bond. An increase in the S=O bond multiplicity relative to a single bond is mainly due to hyperconjugation by the mechanism n(O)→σ*(C -S) and n(O)→σ*(C -S) and, to a lesser extent, by interaction of the oxygen lone electron pairs with the Rydberg orbitals of the S atoms, characterized by a large contribution of the d component.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 1, 2005, pp. 96–104.Original Russian Text Copyright © 2005 by Bzhezovskii, Il’chenko, Chura, Gorb, Yagupol’skii.     

Reverse inductive effect in the series of trans-3,4-disubstituted thiolane 1,1-dioxides

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, p. 993, July, 1990.     

Potential Functions of Internal Rotation around the Csp2-S Bond and Intramolecular Interactions in Thioanisoles p-RC6H4SCH3

The potential functions of internal rotation around the Csp²-S bond in the compounds p-RC6H4S· CH3 (R = NH₂, OCH₃, CH₃, H, F, Cl, CN, NO₂) are studied by ab initio quantum-chemical calculations taking into account the correlation energy for all the electrons (MP2/6-31G*) and in the approximation of the density functional theory (B3LYP/6-31G*). As the electron-donor power of the p-substituents decreases and their electron-acceptor power grows, the molecular conformation changes in the sequence orthogonal-free rotation-planar. The interaction of the sulfur lone electron pairs with the aromatic ring is studied by the natural bond orbital method. The effect that the conformational changes occurring upon replacement of p-substituents exert on the electron density redistribution is demonstrated. The first Koopmans ionization potentials and the geometric parameters of the molecule are reported.     

Synthesis of 2-thiabicyclo[3.2.0]hept-3-enes by reaction of acetylene with sodium sulfide

The previously unknown2-thiabicyclo[2.3.0]hept-3-ene and exo- and endo-6-methyl-2-thiabicyclo[3.2.0]hept-3-enes were synthesized in one step from acetylene and sodium sulfide in aqueous dimethyl disulfoxide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7. pp. 895–899, July, 1976.