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Фешин, В. П.; Фешина, Е. В.

doi:10.1023/a:1013911028791

Cited by 6 publications

(12 citation statements)

References 2 publications

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“…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]). …”

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confidence: 72%

“…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%

“…see [3][4][5][6]). For these compounds it was shown that an increase in the electronegativity or negative charge on the M atom lowers the 35 Cl NQR frequency (increasing the p σ -electron density of the Cl atom) and, conversely, a lowering of the electronegativity or an increase in the positive charge on the M atom increases the 35 Cl NQR frequency (lowering the p σ -electron density of the Cl atom) (e.g.…”

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

confidence: 99%

“…The lower 35 Cl NQR frequency for the axial Cl atom than the equatorial in cyclic α-chloro ethers is explained by the different polarization of the axial and equatorial C-Cl bonds under the influence of the charge on the O atom directly through the field. The degree of polarization of the C-Cl bond caused by the charge on the O atom depends on the orientation of the unshared pair of electrons relative to this bond [3,4].…”

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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confidence: 72%

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

confidence: 99%

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

confidence: 99%

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

confidence: 99%

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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NQRS Data for C4H6Cl2O2 (Subst. No. 0685)

Chihara¹,

Nakamura²

2010

Landolt-Börnstein - Group III Condensed Matter

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Electronic and spatial structure of five-membered oxygen-or sulfur-containing cyclic phosphorus and arsenic compounds based on quantum-chemical calculations

Фешин

Фешина

Zhizhina

2006

Chem Heterocycl Compd

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We have carried out nonempirical quantum-chemical calculations for five-membered heterocyclic molecules containing O or S atoms and also P or As atoms in the ring, using RHF/6-31G(d) and MP2/6-31G(d) methods with full optimization of their geometry. We have studied their electronic and spatial structure and the characteristics of the interaction between atoms in the molecules.Keywords: five-membered oxygen-or sulfur-containing cyclic phosphorus and arsenic compounds, quantum chemical calculations, electronic and spatial structure.For oxygen-containing compounds 1 and 2, the 35 Cl NQR frequencies at 77 K are significantly lower than for the corresponding sulfur-containing analogs 3 and 4 (Table 1) [1, 2], which indicates higher electron densities on the Cl atoms in 1 and 2. This is explained by the fact that the sulfur atom is leas capable of p π -σ conjugation than the oxygen atom [2]. We hypothesize that such a ratio of the NQR frequencies and electron densities for these oxygen-and sulfur-containing compounds is because of polarization of the Z-Cl bonds due to the action of the charge on the S or O atom directly through the field, as in other compounds containing a nonlinear triatomic group Y-Z-M or Y-Z=M (see, for example, [3][4][5][6]). The negative charge on the oxygen atoms in molecules 1 and 2 should be significantly higher than on the sulfur atoms in molecules 3 and 4, which also should lead to the observed ratio of electron densities on the Cl atoms and the NQR frequencies for these compounds. Cl H H H H M(1) M(2) Z C(1) C(2) 1-4 1 Z = P, M(1) = M(2) = O; 2 Z = As, M(1) = M(2) = O; 3 Z = P, M(1) = M(2) = S; 4 Z = As, M(1) = M(2) = S

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Cited by 6 publications

References 2 publications

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

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

NQRS Data for C4H6Cl2O2 (Subst. No. 0685)

Electronic and spatial structure of five-membered oxygen-or sulfur-containing cyclic phosphorus and arsenic compounds based on quantum-chemical calculations

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