V. V. Klochkov

Spatial structure of phosphorus-containing heterocycles: Communication 26. Synthesis and structure of 2-dialkylamino-1,3,2-dioxaphosphepanes with a planar group of atoms in the ring

ConclusionsAn investigation of the PMR spectra over a wide temperature range in different solvents, the dipole moments, and the Kerr constants of 2-dialkylamino-1,3,2-dioxaphosphepanes with a planar group of atoms in the heterocycle (benzene ring, multiple bond) has demonstrated the existence of a conformational equilibrium between the chair form with equatorial position of the dialkylamino group and the twist form.

Stereochemistry of seven-membered heterocycles. 3. Conformation of 5,6-dichloro-1,3-dioxacyclopent-5-enes and the planar-fragment effect

Conclusions1.It is shown by dipole-moment measurements and IR and PMR spectroscopy that 2-R-5,6-dichloro-1, 3-dioxacyclohept-5-enes (R=C6H5, p-ClC6H4, p-NO2C6H4 and the corresponding cyclohexanone ketal exist in the flexible form; the 2-t-butyl analog exists in a chair-e-twist equilibrium depending on the polarity of the medium.2.It is shown that a conformational planar-fragment effect occurs as a result of shielding of the C-Cl and C-H bonds in the chair form.

13C NMR spectroscopy of peroxide derivatives of cyclanes and cyclic peroxides

Conclusions1.The13C NMR spectra of peroxide derivatives of cyclanes and cyclic peroxides have been investigated.2.Replacement of the exocyclic OH group by OOH for saturated cyclic systems leads to a displacement of the signals from the α-carbon downfield by 13.0 ppm, while the β-carbon is displaced upfield by 4.5 ppm, without any dependence on the size or conformational structure of the rings. Replacement of the transannular 00 group by CH2CH2 or CH2O increases the shielding of the quaternary carbon adjoining it.

Steric structure of phosphorus-containing heterocycles. Communication 37. 2-Phenoxy-5,6-benz-1,3,2-dioxaphosphepines with tetracoordinated phosphorus atom

Conclusions1.2-Phenoxy-2-oxo(thiono, seleno)-5,6-benz-1,3,2-dioxaphosphepines in solutions of nonpolar solvents are characterized by an equilibrium of two chair-like forms, which in the case of the sulfide and selenide is shifted in the direction of a conformer with an equatorial orientation of the phenoxyl group; in the oxide, at equilibrium, the proportions of two conformers are approximately the same. In solutions of polar solvents, a three component equilibrium is observed for the oxide, in which the flexible forms as well as the chair-like forms are present.2.In accordance with the dipole moments and Kerr effect data, in all conformations, the compounds studied are characterized by a gauche conformation of the phenyl group in relation to the P=O (P=S, P=Se) bond and by an orthogonal disposition of the benzene ring π-orbitals and the p-unshared electron pair on the exocyclic oxygen atom.

Stereochemistry of 2-substituted 5,6-benzo-1,3,2-dioxarsepines

Conclusions1.2-Chloro- and 2-bromo-5,6-benzo-1,3,2-dioxarsepines have the chair conformation with axial arrangement of the exocyclic bond at the arsenic atom.2.In the case of 2-phenyl-, 2-(p-bromophenyl)-, and 2-(p-nitrophenyl)-5,6-benzo-1,3,2-dioxarsepines an equilibrium exists in solution between the chair-a and twist conformers, the ratio of which is close to unity.13C NMR spectra of “frozen conformers” at 143°K have been obtained for the first time for such a series of compounds.

Conformational properties of 4,4,7,7-tetramethyl-2-hetero-1,3-dioxepanes

Summary4,4,7,7-tetramethyl-1,3-dioxepane and 2,2,4,4,7,7-hexamethyl-2-sila-1,3-dioxepane exist in solution in the twist-boat conformation.

Steric structure of phosphorus-containing heterocycles Communication 36. 2-dialkylamino-1,3,2-dioxaphosphepines with tetracoordinated phosphorus

ConclusionsIn conformity with the data of1H NMR, DM, and the Kerr effect for 2-dialkylamino-2-oxo(thiono, seleno)-1,3,2-dioxaphosphepines, a conformational equilibrium of two forms of twist and chair with an equatorial dialkylamino group is observed in solutions. The equilibrium is displaced in favor of the latter.

Stereochemistry of seven-membered heterocycles 11. Isoenergy chair-twist conformation equilibrium in phthalylformal and its 2-phenyl derivative

ConclusionsBy means of dynamic13C NMR, spectra have been obtained for the “frozen” chair and twist conformers of phthalylformal and its 2-phenyl derivative. The γ-effects of the phenyl substituent have been analyzed for both conformational species. 2. The introduction of a phenyl group into position 2 of phthalylformal is not reflected in the magnitude of the conformational free energy.

PMR investigation of internal inhibited rotation in N1,N1-dimethyl-N2-trifluoro[chloro]acetylamidines of picolinic and nicotinic acids

SummaryHindered rotation around then