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Фешин, В. П.; Фешина, Е. В.

doi:10.1023/a:1017544902053

Cited by 8 publications

(17 citation statements)

References 1 publication

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“…Recently we have established that the 35 Cl NQR frequencies (ν) and asymmetry parameters (η) of the electric field gradient (EFG) at 35 Cl nuclei as calculated using equations 1 and 2, [1][2][3] and populations of the less diffuse 3p-components of the chlorine atom valence porbitals in chlorine-containing molecules calculated with the Hartree-Fock method RHF/6-31G(d), satisfactorily conform to the corresponding experimental 35 Cl NQR data (e.g. refs [3][4][5] ).…”

Section: Introductionsupporting

confidence: 68%

Control of ab initio calculation correctness of the electron distribution in chlorine-containing molecules using 35Cl NQR data

Фешин¹,

Фешина²

2002

Arkivoc

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Ab initio calculations of 2-chlorodioxene and 1-chloro-1-methoxycyclohexane were performed with total optimization of their geometry using the Hartree-Fock theory and the split valence basis set 6-31G(d). The 35 Cl frequencies at 77K for these compounds were obtained as well.These frequencies were compared with those resulting from ab initio calculations. This comparison allows controlling the correctness of ab initio calculations of electron distribution in chloro-containing molecules using 35 Cl NQR data.

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Section: Introductionsupporting

confidence: 68%

Control of ab initio calculation correctness of the electron distribution in chlorine-containing molecules using 35Cl NQR data

Фешин¹,

Фешина²

2002

Arkivoc

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“…A similar anomalous increase in the p σ -electron density of the Cl atom (not related to the electronegativity of the M atom and the inductive effect of its substituent) is observed in other non linear triatomic Cl-C-M groupings with an electron acceptor M atom (e.g. see [3,5]). This is explained by the polarization of the C-Cl bond through the action of the M atom directly through the field (e.g.…”

Section: -H Axial and Equatorial Bond Lengths (D) And Charges (Q) Onsupporting

confidence: 57%

“…The distribution of the electron density in these 2-substituted oxygen containing compounds are significantly different and have a character reverse to that observed for the axial and equatorial atoms found in other ring positions (e.g. see [2][3][4][5][6]). …”

mentioning

confidence: 77%

“…We have previously studied features of the electronic distribution in α-chloro ethers including the cyclic tetrahydropyran [2] and 1,4-dioxane [3][4][5]. It was found that the O atom markedly increases the p σ -electron density of the axial Cl atom situated geminally to it.…”

Section: -H Axial and Equatorial Bond Lengths (D) And Charges (Q) Onmentioning

confidence: 99%

“…This is explained by the polarization of the C-Cl bond through the action of the M atom directly through the field (e.g. see [3][4][5][6]). 2-Chloro-N-methylpiperidine does not prove an exception.…”

Section: -H Axial and Equatorial Bond Lengths (D) And Charges (Q) Onmentioning

confidence: 99%

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

Фешина

Zhizhina

Фешин

2005

Chem Heterocycl Compd

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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 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 ClCH 2 NH 2 molecule has been studied by the RHF/6-31(g) method for different angles of rotation of the ClCH 2 group around the C-N bond.Keywords: N-methylpiperidine and its chloro-substituted derivatives, piperidine, axial and equatorial atoms, quantum-chemical calculations, 35 Cl NQR frequencies.As a rule, substituted piperidines exist in a chair form (e.g. see [1]). There is conflicting data regarding the relative orientation of a substituent on the nitrogen atom and in the ring. NMR Data is considered to be (e.g. see [1]) the most reliable for the case of R = H and this points to an axial position for the hydrogen atom (Form 1). For R = alkyl all available data indicates an equatorial position for an alkyl group (Form 2).For a substituent in the ring of substituted piperidines as well as in substituted cyclohexanes the generally more favored orientation is an equatorial position. However, in 2-substituted piperidines, as in 2-substituted tetrahydropyrans, 1,4-dioxanes, cyclohexanones, etc, an electron-acceptor substituent usually occupies an axial position (e.g. see [1]). The distribution of the electron density in these 2-substituted oxygen containing compounds are significantly different and have a character reverse to that observed for the axial and equatorial atoms found in other ring positions (e.g. see [2][3][4][5][6]).The aim of our work is to examine by nonempirical, quantum-chemical methods the conformational features of substituted piperidines, the effect of the nitrogen atom on the electron densities of the Cl and H atoms in variously substituted chloro N-methylpiperidines, and also to study the 35 Cl NQR parameters in the latter. For this task we carried out quantum-chemical calculations of the molecular forms 1-10 via full optimization of their geometry by the Hartree-Fock method on a 6-31G(d) split valence basis using the Gaussian 94W program [7].

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Conformational Features of Monochloro-substituted Tetrahydropyrans According to Data from ab initio Calculations and 35Cl NQR

Фешин

Zhizhina

Фешина

2005

Chem Heterocycl Compd

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Nonempirical quantum-chemical calculations of 2-, 3-, and 4-chloro-substituted tetrahydropyrans by the and 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.Keywords: chlorine-substituted tetrahydropyrans, axial and equatorial bonds, conformational energy, RHF/6-31G(d) and MP2/6-31G(d) calculations.Six-membered saturated heterocyclic compounds and their substituted derivatives, like cyclohexane derivatives, exist predominantly in the chair form. Monosubstituted cyclohexanes with the substituent in the equatorial position are energetically more favorable than those with the axial position. If there is an oxygen atom in the ring, the stability changes in the reverse order. This is considered one sign of an "anomeric effect" (e.g., [1][2][3]).In view of the nature of interaction between the geminal atoms Y and M in organic and heteroorganic molecules containing a triatomic group Y-C-M (e.g., see [4]) it must be assumed that the axial position of the substituent in the tetrahydropyran is not always energetically more favorable but is only preferred in the case where the substituent is in the geminal position in relation to the oxygen atom. At a long distance from the latter the substituent will prefer the equatorial position, as in cyclohexane derivatives, since the effect of the oxygen atom will no longer be as strong. This suggestion is easily checked by carrying out quantum-chemical calculations for the various isomers of monosubstituted tetrahydropyrans, such as the chloro-substituted derivatives, and this is also useful during study of the nature of the anomeric effect.The results of our restricted Hartree-Fock calculations with allowance for electron correlation according to second-order Möller-Plesset perturbation theory using the split valence basis set 6-31G(d) are given here. In calculations using Gaussian 94W software [5] the origin of the system of coordinates was located at the nucleus of the Cl atom, while the z axis was directed along the Cl-C bond. The obtained results were compared with experimental data from the 35 Cl NQR spectra [6] and were used for a more detailed interpretation of the latter.

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Cited by 8 publications

References 1 publication

Control of ab initio calculation correctness of the electron distribution in chlorine-containing molecules using 35Cl NQR data

Control of ab initio calculation correctness of the electron distribution in chlorine-containing molecules using 35Cl NQR data

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

Conformational Features of Monochloro-substituted Tetrahydropyrans According to Data from ab initio Calculations and 35Cl NQR

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