Equilibrium distribution of E–Z-ketimine isomers

Bjørgo, Johannes; Boyd, Derek R.; Watson, Christopher G.; Jennings, W. Brian

doi:10.1039/p29740000757

Cited by 39 publications

(31 citation statements)

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“…Imines with different substituents on the imino carbon can exhibit E-Z isomerism at ambient temperature, but at elevated temperatures rapid isomerisation is often observed. 13,14,27 When crystals of imine 1 were dissolved in deuteriochloroform and the 1 H NMR spectrum recorded immediately a single set of signals was observed consistent with the proposed structure. However an aromatic doublet signal ( 3 J 6.9 Hz) which integrated for two hydrogens was abnormally shielded at δ 6.50.…”

Section: Model Compounds 1 and 2 Possessing A 3-pyridyl Ringmentioning

confidence: 57%

Stereodynamics and edge-to-face CH–π aromatic interactions in imino compounds containing heterocyclic rings

et al. 2017

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By comparison with close contact interactions between benzene rings there is a paucity of experimental data available for attractive interactions involving aromatic heterocyclic rings, especially for small molecules in solution. Herein we describe aromatic heterocyclic and carbocyclic edge-to face interactions and conformational stereodynamics of N-1,2-diphenylethyl imines bearing a phenyl group and either a 2-pyridyl, 3-pyridyl, 2-thiophene or 2-furanyl moiety on the imino carbon. X-ray crystal structures have been determined for two compounds. Slow rotation about the phenyl-imino bond in the E-isomers and around the heterocycle-imino bond in the Z-isomers of the pyridyl compounds was observed at low temperatures by NMR. Abnormally large shielding of one ortho hydrogen indicates that both the imino phenyl and heterocycle rings can engage in an edge-to-face interaction with the N-terminal phenyl moiety in the appropriate isomer. Some rotational barriers around the phenyl-imino and heterocycle-imino bonds were measured.

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Section: Model Compounds 1 and 2 Possessing A 3-pyridyl Ringmentioning

confidence: 57%

Stereodynamics and edge-to-face CH–π aromatic interactions in imino compounds containing heterocyclic rings

et al. 2017

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“…Two series of oxaziridines have also been included in this study; the 13C NMR spectra of this class of compound have received relatively little attention. '"12 C NMR spectra of imines have 13 …”

Section: In Recent Years Several Papers Concerned Withmentioning

confidence: 99%

Dynamic stereochemistry of imines and derivatives: 15—Carbon‐13 NMR studies of aryl‐substituted imines and oxaziridines

Jennings¹,

Wilson²,

Boyd³

et al. 1983

Org. Magn. Reson.

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C chemical shifts for several series of cis-and truns-iV-alkylimines and oxaziridines bearing parasubstituted C-phenyl rings are reported and correlated with dual substituent parameters. The 13C=N and oxaziridine ring carbon shifts correlate primarily with the inductive/field parameters, ul, whereas both resonance and inductive terms generally contribute about equally to the long-range substituent effects on -1 side-chain chemical shifts. Correlations on diastereoisomeric imines show that the transmission of substituent effects can be significantly affected by the E Z configuration. Aromatic carbon chemical shifts in imines are discussed in relation to the E Z configuration and the conformation around the aryl-imino bond. 13

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“…The interconversion from E-to Z-isomers of imines has been the object of many theoretical and experimental studies which have addressed questions on the mechanism, kinetics and thermodynamics of this process 16,[27][28][29][30][31][32][33][34] . These studies pointed out that in aprotic medium, isomerization occurs by inversion of the nitrogen atom, as indicated in Scheme 2.…”

Section: Introductionmentioning

confidence: 99%

Theoretical and experimental investigation of the formation of E- and Z-Aldimines from the reaction of methylamine with acetaldehyde

Pliego¹,

Alcântara²,

Veloso³

et al. 1999

J. Braz. Chem. Soc.

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A reação entre metilamina e acetaldeído em pentano a 230 K leva à formação das aldiminas Ee Z-, sendo o isômero Z-o produto principal e gerado sob controle cinético. O isômero E-é mais estável do que o Z-por 3.3 kcal/mol (∆G*). Os cálculos ab initio mostraram que a etapa bimolecular de adição ocorre por um processo concertado, com formação da ligação C-N e transferência de próton através de um estado de transição de quatro centros. O intermediário zwiteriônico, frequentemente invocado neste tipo de reação, não existe como um mínimo na superfície de energia potencial. Entretanto, a energia livre de ativação para o mecanismo concertado é muito alta, e não é capaz de explicar a cinética deste processo. O mesmo acorre com a etapa de eliminação de água para formar a imina, ou seja, possui uma barreira de ativação muito alta. Estes resultados implicam que tanto a etapa de adição, como a de eliminação, devem ocorrer por um mecanismo de catálise.O isômero Z-pode se interconverter para a forma E-através de uma inversão sobre o nitrogênio sp 2 . A 298.15 K, a energia livre de ativação para este processo foi calculada como sendo 27.0 kcal/mol, o que leva a um tempo de vida de quatro meses para este isômero.The reaction of methylamine with acetaldehyde in pentane at 230 K leads to formation of both E-and Z-aldimines, the Z-isomer being the main product and generated upon kinetic control. The E-form is more stable than the Z-form by 3.3 kcal/mol (∆G*). Ab initio calculations have indicated that a tetrahedral zwitterion intermediate is not formed, and the bimolecular process, forming the aminoalcohol intermediate, occurs through a four center transition state, with concerted formation of C-N bond and proton transfer. However, the predicted ∆G* ≠ is very high, indicating that the true mechanism for this step is not bimolecular. A catalyzed pathway must be actuating. The following step, unimolecular elimination of water, also presents a very high activation free energy. Similarly, a catalyzed mechanism is needed. The isomerization from the Z-form to the E-form through inversion of the nitrogen atom has a predicted ∆G* ≠ of 27.0 kcal/mol at 298.15 K, resulting in a lifetime of four months for the Z-isomer.

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Equilibrium distribution of E–Z-ketimine isomers

Cited by 39 publications

References 0 publications

Stereodynamics and edge-to-face CH–π aromatic interactions in imino compounds containing heterocyclic rings

Stereodynamics and edge-to-face CH–π aromatic interactions in imino compounds containing heterocyclic rings

Dynamic stereochemistry of imines and derivatives: 15—Carbon‐13 NMR studies of aryl‐substituted imines and oxaziridines

Theoretical and experimental investigation of the formation of E- and Z-Aldimines from the reaction of methylamine with acetaldehyde

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