B. A. Trofimov

Effect of the nitrogen unshared electron pair on the direct13C-13C spin-spin coupling constant of a neighboring bond in oximes

The authors have previously established that the direct /sup 13/C-/sup 13/C coupling constants are stereospecific relative to the orientation of unshared electron pairs (UEP) of nitrogen and oxygen atoms. Here they show that the nitrogen UEP produces a positive contribution to the direct /sup 13/C-/sup 13/C coupling constant of an adjacent syn-periplanar carbon-carbon bond and not to a negative contribution of the corresponding constant of the anti-periplanar bond. Thus, the observed effect is not a consequence of the interaction of the heteroatom UEP with the anti-bonding orbital of the adjacent anti-periplanar bond (n/sub o-o/* interaction) as in the case of anomeric and related effects.

NMR-13C spectra and effects of conjugation in alkoxy- and alkylthioethylenes

1. The NMR-13C spectra of a number of vinyl alkyl sulfides was studied. An analysis of the chemical shifts of the carbons of the multiple bond gives unambiguous evidence that weak p-π conjugation of the heteroatom with the multiple bond, the intensity of which is three times lower than in vinyl alkyl ethers, operates in these compounds. 2. The chemical shifts of13Cβ in the series of vinyl alkyl sulfides and ethers show that in both cases the degree of p-π conjugation is determined by the steric inhibition of resonance, which is more pronounced in the series of sulfides.

Effects of conjugation and the conformational structure of aromatic selenides

ConclusionsIn the aromatic selenides, in contrast to the corresponding sulfides, the partial steric inhibition of the conjugation of the Se atom with the aromatic π-system occurs. The appreciable content (∼30%) of the plane conformer is observed in compounds with the tertiary and quaternary α-carbon atoms of the alkyl group; this explains the weak π-donor properties of Se in relation to the aromatic fragment.

Synthesis of monosubstituted divinyl sulfides

ConclusionsSodium ethenethiolate obtained from readily available divinyl sulfide reacts with allyl chloride and phenylacetylene to form vinyl 1-propenyl sulfide and vinyl styryl sulfide.

Formation of thiophene by pyrolysis of divinyl sulfoxide

ConclusionsThe main product of the gas-phase pyrolysis of divinyl sulfoxide at 400° is thiophene (up to 60% yield). Paraldehyde, H2O, H2S, and SO2 are also formed here.

Study of conjugation effects by means of NMR spectroscopy. 13. NMR spectra of divinyl chalcogenides

Conclusions1.Parameters of the1H,13C,17O,77Se, and125Te NMR spectra have been obtained for divinyl chalcogenides. Estimates have been made of the effective group electronegativities and the resonance constants of the XCH=CH2 and XCH2CH3 groups, with X=O, S, SO, SO2, Se, and Te.2.In the interaction with the unsaturated fragment, for the Group VI-A heteroatoms, theπ-donor effect predominates, decreasing in the series O>S>Se>Te;π-acceptor interaction is manifested in the series of sulfoxides and sulfones.

NMR-spectroscopic study of conjugation effects. 9.13C NMR spectra of alkyl vinyl sulfoxides and sulfones

ConclusionsPolarization and steric effects of the alkylhetero groups have the main influence on the C1,2 chemical shifts of the vinyl fragment in alkyl vinyl sulfoxides and sulfones. In sulfones, an appreciable role can be played by a π-acceptor interaction between the sulfur atom and the double bond.

Reaction of ethyl vinyl sulfide and divinyl sulfide with triethyl- and triethoxysilane

ConclusionsThe reaction of ethyl vinyl sulfide and divinyl sulfide with triethyl and triethoxysilane in the presence of H2PtCl6 and (Ph3P)3RhCl has been studied. The hydrosilylation of ethyl vinyl sulfide and divinyl sulfide proceeds nonselectively, giving a mixture of two isomeric adducts, the major product being the Farmer addition product. The hydrosilylation of divinyl sulfide is accompanied by secondary reactions, the main one being hydrosilaneinduced cleavage of the bond between the sulfur atom and the vinyl group.

Application of NMR spectroscopy to the study of coupling effects

1. Study has been made of the NMR13C spectra of various alkylthio- and alkoxybenzenes. 2. Data on the benzene-ring13C chemical shift indicate that the shift results from p-π coupling of the hetero atom with the unsaturated fragment, a factor which is more significant in the alkoxybenzenes than in the alkylthiobenzene. The degree of p-π coupling is determined by steric inhibition of resonance. 3. The effect of the alkyl substituent on the coupled hetero atom-unsaturated fragment system is the same in the alkyl phenyl and alkyl vinyl ethers and sulfides.

Stereospecific synthesis of cis-4-phosphonomethyl-1,3-dioxolanes by addition of dialkyl phosphites to divinyl ethers of gem-diols

1. The homolytic addition of dialkyl phosphites to the divinyl ethers of gem-diols leads to the formation of 5-methyl-4-phosphonomethyl-1,3-dioxolanes. 2. The cyclization goes stereospecifically with the formation of the cis-5-methyl-4-(dialkylphosphonomethyl)-1,3-dioxolanes. The degree of stereospecificity is 93–95%.