Vinyl group, coupling constants

Z-Configuration of the initial compounds does not change in the reaction course, as indicated by the coupling constants of the methoxyethenyl group vinyl protons of the triazoles 166 and 167. Adducts of -configuration are present only as admixtures (83DIS). 

H and 13C NMR Data. Typical proton and carbon NMR data for a,(3-unsaturated carbonyl compounds with a terminal vinylic CF2 group are given in Scheme 4.50. The pertinent F—H coupling constants have been given in the previous Scheme 4.49. Conjugation with a carbonyl group deshields the (3-CF2 carbon by 4-5 ppm. 

The coupling constants generally lies between 0 and 20 Hz and depend on the structural relationship between the protons as demonstrated for those of vinyl group. 

In the Horner-Emmons reaction (Scheme 3), the sulfonylphosphonate carbanion 5 is formed in the presence of NaH and then reacts with an aldehyde to produce the intermediate 6 that undergoes in situ elimination to yield the vinyl sulfones and phosphonate anion. The sulfonyl group can stabilize the anion in the sulfonylphosphonate 5. The vinyl sulfones that are produced by this method using aldehydes as starting materials are exclusively the E (trans) isomers. The E-isomers of the vinyl sulfones are shown in the NMR spectra based on the coupling constants of the vinylic protons. Although strongly basic conditions are used in the Horner-Emmons reaction and a-amino aldehydes are easily racemized, the amino acid vinyl sulfones prepared by this method still show substantial optical activity. However, the enantiomeric purity of these compounds has not been determined. 5 ... 

The 1II NMR corroborates diis conclusion since two vinyl protons are observed both in the reactant and product however, a new two-proton doublet appears at 4.155 for die newly produced allylic methylene group. The acid O-H proton is moved far upheld as well. The coupling constants of die vinyl protons (./ = 16 Hz) show the starting compound to be dans, and die large splitting for the downheld vinyl doublet of die product (J = 16 Hz) shows die trails stereochemistry to be maintained in die unsaturated alcohol product. Moreover die splitting between the methylene group and the upheld vinyl proton clearly supports its allylic position. 

Two-bond F-F coupling constants between diastereotopic fluorines in a CF2 group can be quite variable. They can be as small as 14 Hz for some vinylic C=CF2 groups (see Section 4.7.1), of moderate magnitude ( 150 Hz) for cyclopropyl CF2 groups, or as large as 240-285 Hz for diastereotopic, acyclic CF2 groups. 

In the proton spectrum, the vinylic hydrogen appears as a pentet at 8 6.14 with a three-bond F-H coupling constant of 9 Hz, which means that only the equatorial fluorines couple to the hydrogen. There appear to be no examples of the axial fluorine of an SF5 group exhibiting... 

The radical polymerization in aqueous solution of a series of monomers—e.g., vinyl esters, acrylic and methacrylic acids, amides, nitriles, and esters, dicarboxylic acids, and butadiene—have been studied in a flow system using ESR spectrometry. Monomer and polymer radicals have been identified from their ESR spectra. fi-Coupling constants of vinyl ester radicals are low (12-13 gauss) and independent of temperature, tentatively indicating that the /3-CH2 group is locked with respect to the a-carbon group. In copolymerization studies, the low reactivity of vinyl acetate has been confirmed, and increasing reactivity for maleic acid, acrylic acid, acrylonitrile, and fumaric acid in this order has been established by quantitative evaluation of the ESR spectra. This method offers a new approach to studies of free radical polymerization. 

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