Evolution thermique de N-oxydes de dimethylamino-5 alcanols-1 substitues en 5. Competition entre rearrangements de cope et de Meisenheimer

1985 ◽  
Vol 50 (4) ◽  
pp. 956-961
Author(s):  
Didier Barbry ◽  
Bruno Hasiak ◽  
Jean-Michel Augait ◽  
Daniel Couturier
Keyword(s):  
Hydrogen Atom ◽  
Statistical Distribution ◽  
Methyl Ethyl ◽  
Phenyl Substituent ◽  
Electronic Effects ◽  
Vinyl Group ◽  
Acidic Hydrogen

The effect of the substituent R in the position was studied in the decomposition of 1,5-aminoalcohol N-oxides: Meisenheimer rearrangement takes place when R is the vinyl group but is not observed with the phenyl substituent; elimination to alkenol only affects the more acidic hydrogen atom when R is the allyl or benzyl group; with substituents inducing less important electronic effects (methyl, ethyl), the reaction yields an alkenols mixture with statistical distribution.

scholarly journals Effects of substituents on the 1H-NMR chemical shifts of 3-methylene-2-substituted-1, 4-pentadienes

2003 ◽  
Vol 68 (7) ◽  
pp. 525-534 ◽  
Author(s):  
Natasa Valentic ◽  
Gordana Uscumlic
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Electronic Effects ◽  
Resonance Effects ◽  
Charge Densities ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Consistent Picture ◽  
Vinyl Group ◽  
Proton Chemical Shifts

The principle of linear free energy relationships was applied to the 1H chemical shifts of the ?-vinyl proton atoms of 3-methylene-2-substituted-1,4-pentadienes. The correlations of the proton chemical shifts with Swain and Lupton substituent parameters provide a mutually consistent picture of the electronic effects in these compounds. The overall pattern of proton chemical shifts can be largely accounted for by a model of substituent effects based on field, resonance and ? polarization effects. Owing to the particular geometric arrangement of the vinyl group in 3-methylene-2-substituted-1,4-pentadienes, the ?-vinyl protons HB and HC have different sensitivities to polar and resonance effects. The different sensitivities of the 1H chemical shifts to resonance effects reveals some effects not predicted by the model outlined above. Evidence is presented that demonstrates that both the 1H and 13C chemical shifts for these compounds reflect their ground-state charge densities.

scholarly journals Anaerobic and aerobic coproporphyrinogen III oxidases of Rhodopseudomonas spheroides. Mechanism and stereochemistry of vinyl group formation

1983 ◽  
Vol 209 (3) ◽  
pp. 709-718 ◽  
Author(s):  
J S Seehra ◽  
P M Jordan ◽  
M Akhtar
Keyword(s):  
Hydrogen Atom ◽  
Group Formation ◽  
Side Chains ◽  
Improved Method ◽  
Conversion Formula ◽  
Coproporphyrinogen Iii Oxidase ◽  
Rhodopseudomonas Spheroides ◽  
Vinyl Group

An improved method for the preparation of various species of porphobilinogen stereospecifically labelled with 3H in the side chains (at C-6, C-7 and C-8) is described. These labelled samples were used to study the mechanism and stereochemistry of anaerobic as well as aerobic coproporphyrinogen III oxidase of light-grown Rhodopseudomonas spheroides. It was shown that both the oxidases catalyse the conversion of the propionate side chains of coproporphyrinogen III into the vinyl groups of protoporphyrinogen IX, (formula; see text) with the labilization of the pro-S-hydrogen atom at the beta-position. These results are similar to those previously recorded for such conversions in animal and plant systems. In the light of the cumulative information available to date, mechanisms for the conversion, (formula; see text) are discussed and doubt is cast on the participation of hydroxylated intermediates in the process.

Transmission of Electronic Effects through the Vinyl Group. Reactives of the (E)-a-4-Substituted Phenyl-b-pyridineacrylic Acids

Heterocycles ◽  
1994 ◽  
Vol 37 (3) ◽  
pp. 1503 ◽  
Author(s):  
Milica Misic-Vukovic ◽  
Sasa Drmanic ◽  
Bratislav Jovanovic
Keyword(s):  
Electronic Effects ◽  
Vinyl Group

scholarly journals Structure and thermal interconversion of cyclobilirubin IX α

1984 ◽  
Vol 218 (3) ◽  
pp. 667-676 ◽  
Author(s):  
S Onishi ◽  
I Miura ◽  
K Isobe ◽  
S Itoh ◽  
T Ogino ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Chemical Structure ◽  
Lactone Ring ◽  
Final Conclusion ◽  
Quaternary Carbon Atom ◽  
Methyl Group ◽  
Bilirubin Metabolism ◽  
To Come ◽  
Vinyl Group

One of the two main photoproducts in bilirubin metabolism during phototherapy in neonatal hyperbilirubinaemia is (EZ)-cyclobilirubin. However, it has not yet been possible to come to a final conclusion as to its chemical structure, despite the fact that much effort has been expended on the problem. The present paper demonstrates that (EZ)-cyclobilirubin is formed by the intramolecular cyclization of the C-3-vinyl group with the position at C-7 rather than at C-6, without delta-lactone-ring formation. The evidence comes from 13C-n.m.r. spectra, which indicate that an oxygen-bound quaternary carbon atom is not present, and from 1H-n.m.r. spectra, which indicate that the orientation of the methyl group at C-2 is equatorial; these findings are supported by mass spectra. The existence of both an epimeric relationship at C-7 between (EE)- and (EZ)-cyclobilirubins A and B and of steric isomers of the hydrogen atom and methyl group at C-2 is supported by the fact that the methyl-group protons at C-2 and C-7 are observed as a paired signal in 1H-n.m.r. spectra, and that new signals at C-7, C-2 and C-3 beta appear in 13C-n.m.r. spectra, that mass spectra of (EZ)-cyclobilirubins A and B are extremely similar and that, furthermore, thermal interconversion between (EE)- and (EZ)-cyclobilirubins A and B is observed.

Carbon-13 chemical shifts as a probe for conformational and electronic effects in alkyl vinyl ethers

1983 ◽  
Vol 61 (3) ◽  
pp. 488-493 ◽  
Author(s):  
John G. K. Webb ◽  
David K. Yung
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Electronic Effects ◽  
Vinyl Ethers ◽  
Resonance Effects ◽  
Polarization Mechanism ◽  
Chemical Shift Data ◽  
Vinyl Group ◽  
The Relationship ◽  
Geminal Substituent

The principle of additivity of substituent chemical shifts (SCS) is applied to the carbon-13 chemical shifts of β carbons (δβ) in a number of 1,1-disubstituted ethylenes and propenes, which includes some α-substituted alkyl vinyl ethers. An additivity relationship is observed for 34 compounds that indicates an independent polarization mechanism across the double bond for each geminal substituent. Positive deviations from additivity are observed for compounds bearing bulky substituents. The magnitude of deviations is taken as an indication of the severity of steric interactions among substituents.Reductions in efficiency of transmission of substituent effects in ring substituted α-phenyl alkyl vinyl ethers, relative to para-substituted styrenes, are interpreted as the result of a variable dihedral angle between the ring and vinyl group. An explanation of the relationship between conformation and transmission of substituent effects is presented as an alternative to existing views. An angular dependence of π-polarization and resonance effects is consistent with the chemical shift data.

scholarly journals 2,3-Dimethyl-1H-imidazol-3-ium benzenesulfonate–1,2-dimethyl-1H-imidazole co-crystal

IUCrData ◽  
2020 ◽  
Vol 5 (5) ◽  
Author(s):  
Noah Cyr ◽  
Matthias Zeller ◽  
Patrick C. Hillesheim ◽  
Arsalan Mirjafari
Keyword(s):  
Hydrogen Atom ◽  
Imidazole Ring ◽  
Strong Hydrogen Bond ◽  
Methyl Groups ◽  
Benzene Sulfonate ◽  
Asymmetric Unit ◽  
Charge Balance ◽  
Imidazolium Cations ◽  
Sulfonate Anion ◽  
Acidic Hydrogen

In the title co-crystal, C5H9N2 +·C6H5O3S−·C5H8N2, the two 1,2-dimethylimidazole rings exist as partially protonated moieties in the asymmetric unit as a two-part disordered unit wherein the acidic hydrogen atom is bound to each ring. The two imidazolium cations share a strong hydrogen bond via the acidic hydrogen atom, which is disordered between two positions, being bonded to the first versus second imidazole ring in a 0.33 (2) to 0.67 (2) ratio. A benzene sulfonate anion is present for charge balance and interacts with the aromatic H atoms on both imidazole rings as well as with the methyl groups on the rings.

The Use of Styrenes as Embedding Media for Electron Microscopy

1971 ◽  
Vol 29 ◽  
pp. 488-489
Author(s):  
Edward D. De-Lamater ◽  
Eric Johnson ◽  
Thad Schoen ◽  
Cecil Whitaker
Keyword(s):  
Electron Microscopy ◽  
Surface Tension ◽  
Ultraviolet Light ◽  
Methyl Ethyl Ketone Peroxide ◽  
Methyl Ethyl ◽  
Styrene Polymerization ◽  
Radical Initiation ◽  
Tertiary Butyl ◽  
Low Viscosity ◽  
Free Radical Initiation

Monomeric styrenes are demonstrated as excellent embedding media for electron microscopy. Monomeric styrene has extremely low viscosity and low surface tension (less than 1) affording extremely rapid penetration into the specimen. Spurr's Medium based on ERL-4206 (J.Ultra. Research 26, 31-43, 1969) is viscous, requiring gradual infiltration with increasing concentrations. Styrenes are soluble in alcohol and acetone thus fitting well into the usual dehydration procedures. Infiltration with styrene may be done directly following complete dehydration without dilution.Monomeric styrenes are usually inhibited from polymerization by a catechol, in this case, tertiary butyl catechol. Styrene polymerization is activated by Methyl Ethyl Ketone peroxide, a liquid, and probably acts by overcoming the inhibition of the catechol, acting as a source of free radical initiation.Polymerization is carried out either by a temperature of 60°C. or under ultraviolet light with wave lengths of 3400-4000 Engstroms; polymerization stops on removal from the ultraviolet light or heat and is therefore controlled by the length of exposure.

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