Molecular structure of gaseous acetoxime determined by electron diffraction

Iijima, Kinya; Suzuki, Masayuki; Sakaizumi, Takeshi; Ohashi, Osamu

doi:10.1016/s0022-2860(97)00157-9

Cited by 16 publications

(20 citation statements)

References 10 publications

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“…In our opinion, the main stabilizing factor of cis-gauche and cis-cis conformers is the attractive intramolecular C-HÐ Ð ÐN interaction involving a cisoriented methyl C-H bond and nitrogen lone pair like that in N-vinylazoles and related systems. 9 The lowest energy conformer is cis-gauche, in accordance with the gaseous phase electron diffraction data of Iijima et al 8 However, it should be kept in mind that the energy gap between two true-minimum cis-gauche and cis-cis conformers is <1 kJ mol 1 , which implies a very close population of these two forms.…”

Section: Rotational Conformations Of the Methyl Groupssupporting

confidence: 83%

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Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 12—Aliphatic and alicyclic oximes

2005

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One-bond carbon-carbon coupling constants were calculated in a series of nine aliphatic and alicyclic oximes at the SOPPA (second-order polarization propagator approach) level in good agreement with the available experimental data, and several unknown couplings were predicted with high reliability. The experimental difference between J(C,C) of the corresponding carbon-carbon bonds in cis and trans orientations to the nitrogen lone pair is very well reproduced at the SOPPA level, and this provides an additional tool in the configurational assignment at the C=N bond in oximes and related systems.

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Section: Rotational Conformations Of the Methyl Groupssupporting

confidence: 83%

“…11 On the other hand, the higher alicyclic oximes 7-9 adopt predominant conformations of chair (7), twist-chair (8) and boat-chair (9), as shown in Fig. 3.…”

Section: (Z) (E)mentioning

confidence: 98%

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 12—Aliphatic and alicyclic oximes

2005

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“…Thus both the theoretical conformational analysis and electronographic measurements [19] demonstrated that the most stable was cis-gauche conformation.…”

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confidence: 92%

“…We used triply valence-split Pople basis sets 6-311G*, containing polarization d-function for atoms of the second and third periods, 6-311G** incorporating polarization p-functions for hydrogen atoms, and 6-311++G** including diffuse s-functions for hydrogen and s,p-functions for the atoms of the second period. The calculated geometrical parameters were compared with the experimental data obtained by electron diffraction measurements in the gas phase [19].…”

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confidence: 99%

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Spin-spin Coupling Constants 13C-13C in Structural Studies: XXXVIII. Nonempirical Calculations: Oximes

2005

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Ab initio calculation of spin-spin coupling constants 13 C 13 C for a series of ketone oximes was carried out in a framework of the second order polarization propagator approximation (SOPPA). Taking into account the electron correlation effects and the use of special correlation-consistent basic sets including functions allowing for internal correlation and dense functions provided a good agreement between the calculated and experimental values. These results open new possibilities for the configurational assignment of imine nitrogen compounds.Oximes are important semiproducts in the preparative organic sunthesis [1]. In recent years considerable study has been given to ketone oxime reactions with acetylene in superbasic media resulting in O-vinyloximes, pyrroles, and N-vinylpyrroles (Trofimov reaction) [2]. Trofimov reaction ensures an elegant way to previously unavailable or unknown compounds of pyrrole series, and the corresponding yields depend on the structure and configuration of initial oximes. Therefore the estimation of oxime configuration is among the most important problems of pyrrole synthesis [3]. The problems of oximes configuration is also extremely interesting because their isomers differ not only in physical constants but at the same time in chemical properties [4].The configurational structure of imine nitrogen compounds can be unambiguously assigned basing on the measurement the 13 C 13 C coupling constants in the NMR spectra for these values are very sensitive to the orientation of the lone electron pairs (the so-called LEP effect [5]). It was shown theoretically [6] that the LEP effect on the 13 C 13 C coupling constants consisted in a throughspace interaction of the lone electron pair of a heteroatom with a bonding and antibonding orbitals of the neighboring carbon-carbon bonds resulting respectively in an increase and decrease in the s-character of these bonds, i.e., in a positive and a negative contribution into the corresponding J CC constants. The observed stereospecificity of the carbon-carbon coupling constants in oximes and their derivatives makes it possible to use the LEP effect as a reliable and universal criterion for assignment of their configurational isomers [5].A reliable and economical procedure for nonempirical calculation of coupling constants of medium size organic molecules was reported in [7]. The method provides wide prospects for the use ab initio calculations in the theoretical study of the mechanism of the spin-spin coupling. The main goal of the present study is elucidation of the possibility to use procedure [7] for calculation of 13 C 13 C coupling constants in molecules containing multiple bonds and heteroatoms with lone electron pairs. In particular, we were interested whether the LEP effect would be reproduced by nonempirical calculations of 13 C 13 C coupling constants, and also whether this method would be promising for establishing the configuration of imine nitrogen compounds of unknown structure.Here we report the results of ab initio calculations ...

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Spectroscopic and Theoretical Investigations of Monocyclic Dioximes and Dimethoximes with Six-, Eight-, and Ten-Membered Rings

Strenge

Rademacher²

1999

Eur. J. Org. Chem.

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The dioximes 4–6 and the dimethoximes 7–9, which contain the functional groups in opposite positions of a six‐, eight‐, or ten‐membered ring, were synthesized. Their conformational properties and transannular interactions were investigated by spectroscopic (PE, 13C NMR) and theoretical (MMX, AM1, ab initio HF, and B3LYP) methods. While the cyclooctane derivatives 5 and 8 have conformations favourable for through‐space interactions of the π(CN) orbitals, in the other compounds no such interactions can be ascertained. Through‐space orbital interactions in the molecules with an eight‐membered ring lead to a splitting of the π(CN) MOs of 0.4 eV.

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Molecular structure of gaseous acetoxime determined by electron diffraction

Cited by 16 publications

References 10 publications

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 12—Aliphatic and alicyclic oximes

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 12—Aliphatic and alicyclic oximes

Spin-spin Coupling Constants 13C-13C in Structural Studies: XXXVIII. Nonempirical Calculations: Oximes

Spectroscopic and Theoretical Investigations of Monocyclic Dioximes and Dimethoximes with Six-, Eight-, and Ten-Membered Rings

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