Configuration and conformation of alkoxyalkyl and hydroxyalkyl trifluoromethyl nitroxides. Anomeric effects and nitroxide conformations

1981 ◽  
Vol 59 (12) ◽  
pp. 1745-1752 ◽  
Author(s):  
C. Chatgilialoglu ◽  
K. U. Ingold
Keyword(s):  
Anomeric Effect ◽  
Conformational Preference ◽  
Nodal Plane ◽  
Spectral Parameters ◽  
Small Magnitude ◽  
Or Groups ◽  
Steric Factors ◽  
Hyperfine Splittings ◽  
Anomeric Effects ◽  
Configuration And Conformation

The epr spectral parameters for some [Formula: see text] radicals have been measured over a range of temperatures. These radicals are probably non-planar at nitrogen. Their OR groups are in the eclipsed position with respect to the N 2pz orbital, a conformational preference which is attributed to a combination of steric factors and the anomeric effect. For [Formula: see text] the H hyperfine splittings (hfs) are of unusually small magnitude. It is pointed out that all other known [Formula: see text] also have anomalously low H hfs. It is suggested that this is due to the anomeric effect which not only promotes the eclipsed conformation but also causes the OR group to bend towards the semioccupied orbital, thereby moving H and R2 towards the nodal plane of this orbital.

Infrared Group Frequency Correlations for Styrenes, α-Methylstyrenes, and Related Compounds

1986 ◽  
Vol 40 (2) ◽  
pp. 196-203 ◽  
Author(s):  
R. A. Nyquist
Keyword(s):  
Structure Identification ◽  
Ortho Position ◽  
Or Groups ◽  
Group Frequency ◽  
Steric Factors ◽  
Related Compounds

Infrared group frequency correlations are presented which aid in spectra-structure identification of styrenes, α-methylstyrenes, and related compounds. The vinyl and phenyl groups in styrene are coplanar in only those cases where atoms or groups such as Cl and CH3 are not substituted in the 2,6-positions, and the isopropenyl and phenyl groups in α-methylstyrenes are coplanar in only those cases where atoms or groups such as Cl and CH3 are not substituted in one ortho-position. Steric factors prevent the vinyl and phenyl groups from being coplanar in styrene substituted with atoms or groups in at least the 2,6-positions, and steric factors also prevent the isopropenyl and phenyl groups from being coplanar in 2-substituted α-methylstyrenes.

Conformational Preferences of Ethyl 2,3-Dideoxy-3-[(α-D-glucopyranosyl)methyl]-β-L- and -D-arabino-hexopyranosides

2005 ◽  
Vol 70 (12) ◽  
pp. 2086-2100 ◽  
Author(s):  
Ondřej Vích ◽  
Ladislav Kniežo ◽  
Hana Dvořáková ◽  
Ivan Raich ◽  
Štěpán Valenta
Keyword(s):  
The Other ◽  
Glycosidic Bond ◽  
Conformational Behavior ◽  
Anomeric Effect ◽  
Conformational Preference ◽  
Other Hand ◽  
Conformational Preferences

Conformational behavior of two C-disaccharides, containing D-glucopyranose moiety at the non-reducing end and L- or D-2-deoxy-arabino-hexopyranose moiety at the reducing end, has been studied using MM3 calculations and NMR experiments. The obtained results show that the conformational preference around the C-glycosidic bond is the same in both compounds and corresponds with the exo-anomeric effect. On the other hand, both compounds differ markedly in the conformational arrangement around the C-aglycone bond where the population of conformers is controlled by 1,3-diaxial-like interactions.

scholarly journals Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides

Molecules ◽  
2018 ◽  
Vol 23 (11) ◽  
pp. 2834 ◽  
Author(s):  
Stephen Glover ◽  
Adam Rosser
Keyword(s):  
Amide Bond ◽  
Anomeric Effect ◽  
Amide Nitrogen ◽  
Carbonyl Carbon ◽  
Heteroatom Substitution ◽  
Electronegative Atom ◽  
Anomeric Effects ◽  
Acyl Derivatives

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide. However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically. In certain configurations, reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen) reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. In other cases the anomeric effect facilitates SN1 and SN2 reactivity at the amide nitrogen.

The conformational preference of methoxyl and acetoxyl groups in 3-oxycyclohexenes, 2-oxymethylenecyclohexanes, and 1-oxytetralins and the generalized anomeric effect

1987 ◽  
Vol 65 (8) ◽  
pp. 1761-1768 ◽  
Author(s):  
Adama Ouédraogo ◽  
Minh Tan Phan Viet ◽  
John K. Saunders ◽  
Jean Lessard
Keyword(s):  
Methoxyl Group ◽  
Equatorial Orientation ◽  
Anomeric Effect ◽  
Conformational Preference ◽  
Magnetic Resonance Data ◽  
Conformational Effect ◽  
Axial Conformer ◽  
Resonance Data ◽  
Cis And Trans ◽  
Derivatives Of

The 13C and 1H nuclear magnetic resonance data of 3-oxycyclohexenes, 2-oxymethylenecyclohexanes, and 1-oxytetralins show (i) that the pseudoaxial preference is larger for the acetoxyl group than for the methoxyl group in 3-oxycyclohexenes, (ii) that the methoxyl and the acetoxyl groups have the same pseudoaxial preference in 1-oxytetralins, and (iii) that in 2-oxymethylenecyclohexanes, the acetoxyl group prefers the equatorial orientation whereas the methoxyl group prefers to be axial. These results are interpreted in terms of the orbital picture (π–σ* stabilization of the axial conformer) of the generalized anomeric effect to which is opposed a conformational effect termed the "unsaturation effect" in 2-acetoxymethylenecyclo-hexane and probably also, but to a much smaller extent, in 1-acetoxytetralin. The results also show that cis and transtert-butyl analogues of 3-oxycyclohexenes do not represent the true limit conformers whereas cis and trans 4-tert-butyl derivatives of 2-oxymethylenecyclohexanes do not differ drastically from the limit conformers.

Conformational Preference of 2-Triphenylphosphonio-1,3-Dithianes: Competition Between Steric and Anomeric Effects

1991 ◽  
Vol 30 (5) ◽  
pp. 578-580 ◽  
Author(s):  
Marian Mikołajczyk ◽  
Piotr Graczyk ◽  
Michał W. Wieczorek ◽  
Grzegorz Bujacz
Keyword(s):  
Conformational Preference ◽  
Anomeric Effects

Ab initio modelling of the anomeric and exo anomeric effects in 2-methoxytetrahydropyran and 2-methoxythiane corrected for intramolecular BSSE

2015 ◽  
Vol 17 (28) ◽  
pp. 18501-18513 ◽  
Author(s):  
Vladimir Sladek ◽  
Filip Holka ◽  
Igor Tvaroška
Keyword(s):  
Ab Initio ◽  
Anomeric Effect ◽  
Oxygen Substitution ◽  
Anomeric Effects

Oxygen substitution in 2-methoxytetrahydropyran by sulphur in 2-methoxythiane approximately doubles the anomeric effect, which slows down enzymatic processing of 2-methoxythiane.

scholarly journals Toward the origin of the conformational preference of 2-methoxyoxane, a model useful to study the anomeric effect

ARKIVOC ◽  
2003 ◽  
Vol 2003 (11) ◽  
pp. 132-148 ◽  
Author(s):  
Karina Martinez ◽  
Fernando Cortes ◽  
Ingrid Leal ◽  
Vanessa Reyna ◽  
Delia Quintana ◽  
...  
Keyword(s):  
Anomeric Effect ◽  
Conformational Preference
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