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Bzhezovskii, V. M.; Kapustin, E. G.; Трофимов, Б. А.

doi:10.1023/a:1026182819302

Russian Journal of General Chemistry

2003

DOI: 10.1023/a:1026182819302

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V. M. Bzhezovskii

E. G. Kapustin

Б. А. Трофимов

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Cited by 5 publications

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“…One lone electron pair is a hybrid orbital (n s ), and the other, virtually pure p x orbital (n p ). In the hybrid orbitals of the lone electron pairs n s , the These values are close to those obtained previously in the series of aromatic [16] and vinyl [17] compounds with the corresponding heteroatoms. According to the results given in Table 1, in terms of the NBO formalism, n s and n p of the X atoms appreciably differ in the energy.…”

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An ab initio quantum-chemical study of the compounds HC≡CXCH3 (X = O, S, Se)

et al. 2004

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The compounds HC=CXMe (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.Chemical transformations of acetylene and its derivatives allow preparation of new promising monomers, cross-linking agents, and intermediates for fine organic synthesis [1,2]. Understanding of the factors affecting the reactivity of the compounds and development of new synthetic routes are impossible without comprehensive study of their electronic and steric structure by physicochemical and theoretical methods. Modern ab initio quantum-chemical methods taking into account the electron correlation reproduce the experimentally observed molecular characteristics with a high accuracy, without introducing any empirical fitting parameters [3]. Analysis of the wave functions obtained by the method of natural bond orbitals (NBO) allows transformation of the canonical molecular orbitals into orbitals of the Lewis type and interpretation of the results of quantum-chemical calculations in terms of traditional chemistry [4 3 6].Our goal was to apply this approach to the compounds HC=CXMe (X = O, S, Se) and to analyze the quantitative information on the nature of the lone electron pairs of the O, S, and Se atoms, on their interaction with the triple bond, and on their effect on the electron density distribution.Our study was based on ab initio quantum-chemical calculations taking into account the correlation energy for all the electrons on the level of the secondorder Møller3Plesset perturbation theory [3,7] in the 6-31G double-split basis set with six d functions [8]: MP2(full)/6-31G*. The calculations were performed using the GAUSSIAN 98W (Rev. A.7) [9] and GAMESS [10] software. We used standard criteria of convergence of the density matrix and energy gradient. The population analysis of the wave functions was performed with the NBO method [4 3 6]. We obtained the following total energies (E t , au): 3191.2592574 (HC=COMe), 3513.8919695 (HC=CS . Me), and 32514.0062393 (HC=CSeMe). For HC b =C a . OMe, the COC bond angle (113.4o) and the C sp 3O (1.313 A) and C sp 33O (1.434 A) bond lengths have been determined experimentally [11, 12]. We obtained the following structural parameters for this molecule: 112.9o (UCOC); 1.217 [d(C=C)], 1.315 [d(C a 3X)], 1.064 [d(C b 3H)], 1.445 [d(X3CMe)], and 1.088, 1.092, 1.092 A [d(C3H Me )]. The steric structure of HC b =C a SMe was studied by electron diffraction [13] and microwave spectroscopy [14]. The C=C bond length is 1.215(3) [13] or 1.205(7) A [14]; the C sp 3S bond length is 1.683(3) [13] or 1.685(5) A [14], and the C sp 33S bond length, 1.814(3) [13] and 1.813(2) A [14]. The CSC bond angle is 99.9o [13, 14], and the SCC bond angle, 184(3)o [13] or 182(0.3)o [14]. We obtained the followin...

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confidence: 89%

“…and Se atoms with the acetylenic moiety exceeds the energy of the resonance interaction of n p of the respective heteroatoms with the aromatic ring in the C 6 H 5 XMe molecules [16] and with the double bond in the H 2 C=CHXMe molecules [17].…”

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An ab initio quantum-chemical study of the compounds HC≡CXCH3 (X = O, S, Se)

et al. 2004

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“…However, analysis of intramolecular interactions in phenyl and vinyl ethers in terms of the natural bond orbital (NBO) approach [13] showed that the energy of interaction between unshared electron pairs on the oxygen atom and π* orbital of the double bond is considerably higher than the energy of interaction with π* orbitals of the aromatic ring [14][15][16][17]. Therefore, the barrier to internal rotation about the O-C i bond is lower than the barrier to rotation about the O-C α bond, and the torsion angle ψ is more labile than φ.…”

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confidence: 99%

“…According to the results of NBO analysis, the energy of interaction of the unshared electron pair on the oxygen atom with the antibonding orbital of the vinyl C=C bond [electron density transfer n(O σ ) → σ*(C=C)] in the s-cis conformer considerably exceeds the corresponding energy for the s-trans conformer due to more favorable orientation of the interacting orbitals [16]. This contribution to the total energy gives rise to appearance of an energy minimum corresponding to the s-cis structure and hence to s-cis-trans rotational isomerism in the series of vinyl ethers.…”

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confidence: 99%

Effect of aromatic ring anisotropy on the 1H NMR shielding constants and conformational equilibrium of sterically strained aryl vinyl ethers

Afonin

2011

Russ J Org Chem

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According to the 1 H and 13 C NMR data and quantum-chemical calculations, phenyl vinyl ether exists mainly in the s-trans conformation which is characterized by concurrent p-π* interaction of the oxygen atom with both unsaturated fragments. Introduction of two methyl groups into the ortho positions of the benzene ring forces the latter to go out from the vinyloxy group plane, leading to loss of p-π* conjugation with the aromatic ring, enhancement of p-π* conjugation with the vinyl group, and transition of the molecule to s-cis conformation. The 1 H and 13 C NMR data indicated that replacement of both o-methyl groups by tert-butyl makes the s-cis conformer sterically overcrowded even when the aromatic ring is oriented orthogonally with respect to the vinyl group; as a result, conformational equilibrium is displaced again toward s-trans rotamer.I-VI, X = O; IX, X, X = S; I, IX, R 1 = R 2 = R 3 = H; II, R 1 = Me, R 2 = R 3 = H; III, R 1 = R 3 = H, R 2 = Me; IV, X, R 1 = R 2 = R 3 = Me; V, R 1 = R 3 = t-Bu, R 2 = H; VI, R 1 = R 3 = t-Bu, R 2 = Me; VII, R = Me; VIII, R = t-Bu.It was shown previously that stereospecificity of shielding constants of different magnetically active nuclei may be regarded as an effective tool for studying steric and electronic structure of unsaturated heteroatom compounds [1][2][3][4]. The procedure for performing structural studies on organic molecules with the aid of NMR spectroscopy is attractive due to its accessibility and simplicity, for NMR chemical shift is one of the most readily and reliably measurable spectral parameters of a substance. Conformational equilibria in the series of fluorinated aryl vinyl sulfides [5] and selenides [6] were studied previously by analysis of their 1 H and 13 C NMR spectra. In the present study stereochemical relations inherent to 1 H and 13 C shielding constants were used to examine rotational isomerism in the series of sterically strained aryl vinyl ethers having a bulky substituent in the ortho position with respect to the vinyloxy group. Prevalence of one or another rotamer was confirmed by analysis of 1 H-1 H and 13 C-1 H coupling constants in the vinyl group.The 1 H and 13 C NMR parameters of aryl vinyl ethers I-VI, as well as of alkyl vinyl ethers VII and VIII and aryl vinyl sulfides IX and X taken for comparison, are collected in table. As "reference" structure for estimation of the effect of substituents in the aromatic ring on conformational equilibria of aryl vinyl ethers we selected unsubstituted phenyl vinyl ether (I). The steric structure of its molecule is determined by the weight-average torsion angles φ and ψ at the O-C α and O-C i bonds, respectively (structure A).The 13 C NMR spectrum of phenyl vinyl ether (I) revealed pronounced excess shielding of the β-carbon atom in the vinyl group as compared to ethylene (δ C 95 and 123 ppm, respectively), which indicated considerable p-π* interaction in the vinyloxy group [7,8]. Therefore, compound I was presumed to exist as equilibrium mixture of nearly planar s-cis and s-trans conformers (see...

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“…It was found that alkyl vinyl sulfides give rise to rotational isomerism related to internal rotation about the S-C α bond. According to the results of nonempirical quantum-chemical calculations with account taken of electron correlation in terms of the second-order perturbation theory using Pople's triplesplit basis set, the molecule of methyl vinyl sulfide adopts preferentially planar s-cis conformation [3]. The second, less energetically favorable conformer is represented by two quasi-degenerate nonplanar gauche structures separated by a low rotational barrier corresponding to the planar trans conformer [3].…”

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confidence: 99%

Long-range 19F-1H spin-spin coupling as an indication of conformational equilibrium of fluoro-substituted aryl vinyl sulfides

Afonin

2009

Russ J Org Chem

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Long-range 19 F-1 H spin-spin coupling with participation of vinyl group protons, observed in the 1 H NMR spectra of fluoro-substituted aryl vinyl sulfides, indicates that these compounds exist as equilibrium mixtures of s-cis and s-trans rotational isomers.I, R 1 = CH 2 =CHS, R 2 = F; II, R 1 = Cl, R 2 = F; III, R 1 = R 2 = CH 2 =CHS; IV, R = H; V, R = Me.Steric structure of vinyl sulfides having various substituents was studied by several physicochemical methods [1,2]. It was found that alkyl vinyl sulfides give rise to rotational isomerism related to internal rotation about the S-C α bond. According to the results of nonempirical quantum-chemical calculations with account taken of electron correlation in terms of the second-order perturbation theory using Pople's triplesplit basis set, the molecule of methyl vinyl sulfide adopts preferentially planar s-cis conformation [3]. The second, less energetically favorable conformer is represented by two quasi-degenerate nonplanar gauche structures separated by a low rotational barrier corresponding to the planar trans conformer [3]. Therefore, it can be regarded as quasi-s-trans conformer in which molecular fragments move with a large amplitude. Alkyl vinyl sulfides with branched alkyl groups are characterized by predominant s-trans (gauche) conformation [1, 2]. On the other hand, there are no published data on rotational isomerism in the series of aryl vinyl sulfides, though electronic structure of these compounds was examined on the basis of their 13 C NMR spectra [4]. Furthermore, 1 H and 13 C NMR studies on hetaryl vinyl sulfides revealed some conformation-related parameters which can be used to identify predominant spatial configuration [5,6].We previously synthesized several fluoro-substituted aryl vinyl sulfides [7,8] which were used as initial compounds in the synthesis of a large number of more complex derivatives possessing an analogous fragment [9][10][11][12][13]. These compounds clearly displayed in the 1 H NMR spectra long-range spin-spin couplings between 19 F nuclei and proton in the α-position of the vinyl group, and the observed couplings were used to identify regioisomers [10,11]. However, long-range 19 F-1 H coupling with other protons in the vinyl group was not observed previously, and stereochemical conditions ensuring observation of such coupling were not discussed in studies on the synthesis of fluoro-substituted aryl vinyl sulfides. The present communication reports on the use of long-range 19 F-1 H spin-spin couplings involving α-and β-protons in the vinyl group, as well as of other conformation-dependent 1 H and 13 C NMR parameters, in experimental study on rotational isomerism of fluorine-containing aryl vinyl sulfides I-III. The populations of different rotamers of I-III and unsubstituted phenyl vinyl sulfide IV were compared on the basis of other conformation-related parameters of their 1 H and 13 C NMR spectra.

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Untitled

Cited by 5 publications

References 39 publications

An ab initio quantum-chemical study of the compounds HC≡CXCH3 (X = O, S, Se)

An ab initio quantum-chemical study of the compounds HC≡CXCH3 (X = O, S, Se)

Effect of aromatic ring anisotropy on the 1H NMR shielding constants and conformational equilibrium of sterically strained aryl vinyl ethers

Long-range 19F-1H spin-spin coupling as an indication of conformational equilibrium of fluoro-substituted aryl vinyl sulfides

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