Application of NMR spectroscopy to the study of the three-dimensional structures of hydrogenated heterocycles (review). II. Configurations and conformations of the heterorings

The results of determinations of the configurations and conformations of heterorings containing N, O, Si, P, S, Ge, As, Sn, Se, Sb, and Te atoms by 1H, 13C, 15N, 19F, and 13P NMR spectroscopy are correlated. Publications that are of interest from a methodical point of view are primarily summarized in the review. © 1981 Plenum Publishing Corporation

Application of NMR spectroscopy for the study of the three-dimensional structures of hydrogenated heterocycles (review)

A review of the dependences of the direct, geminal, vicinal, and long-range spin-spin coupling constants on the valence, dihedral, and torsion angles, and on the electronegativities and orientations of the heteroatoms is given. The empirical and nonempirical dependences for the constants with participation of the nuclei of the 1H, 13C, 14N, 15N, 19F, 31P, 29Si, 119Sn, and 199Hg isotopes are presented. © 1979 Plenum Publishing Corporation

Nuclear magnetic resonance spectra of protons and structure of azines and phenylhydrazones

1. The high-resolution PMR spectra of azines, phenyl- and methylphenyl-hydrazones of aliphatic ketones and aldehydes were obtained and deciphered. 2. On the basis of an analysis of the data obtained, conclusions were drawn on the hydrazone structure of the compounds studied in the free state. 3. Using the data obtained and the theory of the magnetic anisotropy of aromatic rings, calculations were made of the probable configuration of the acetaldazine, dimethylketazine, acetone phenyl- and methylphenyl-hydrazones, and acetaldehyde methylphenylhydrazone molecules. 4. A study of the influence of temperature on the PMR spectrum of acetone methylphenylhydrazone within the interval from -14 to +80° indicated the absence of free rotation of the phenyl radical around the C-N bond. © 1966 Consultants Bureau

Diagrams of isoshielding lines of C-N bonds and nitrogen and phosphorus lone pairs

Diagrams of isoshielding lines in the vicinity of lone pairs of nitrogen and phosphorus atoms, as well as a C-N bond, have been calculated. The magnetic shielding constants of the protons were calculated by the gauge-invariant atomic-orbital method with the use of localized molecular orbitals and expansions of the atomic wave functions in Gaussian functions. The diagrams of the isoshielding lines have been used for the evaluation of chemical shifts in piperidine derivatives for the purpose of accounting for the experimentally observed tendencies in chemical shifts. © 1986 Plenum Publishing Corporation

Stereospecificity in the proton magnetic relaxation rate of enantiotopic methyls and the methyl rotation barrier

It is proposed that a distinction should be made between stereospecificity of the first kind, which provides spectral (line assignments in the NMR spectrum) and structural (molecular conformations) information, and stereospecificity of the second kind, which only provides spectral information, on the basis of the relaxation times T1. The nature of the stereospecificity was revealed in detail during analysis of the reasons for the differences in the proton relaxation times of enantiotopic gem-dimethyl groups in the conformationally rigid molecule of 2-oxo-5,5-dimethyl-1,3,2-dioxathiane. It is suggested that the barrier to rotation of the methyl in the geminal CH3-C-H fragment can be assessed from the temperature dependence of the t1 time of the methine proton. The experiment was carried out with the stereoisomeric r-2-tert-butyl-4-methyl-trans-7-methyl[2]1,3-dioxepane. © 1987 Plenum Publishing Corporation

Stereochemistry of organophosphorus compounds 15. Synthesis and permutational lability of 1,6,10-trioxa-8,8-dimethyl[(5-methoxy)-5-phosphaspiro(4.5)]dec-2-ene

1. We have synthesized 1,6,10-trioxa-8,8-dimethyl[(5-methoxy)-5-phosphaspiro(4.5)]dec-2-ene, a compound in which the trigonal-bipyramidal phosphorus bond arrangment undergoes pseudorotation at temperatures below 36°C. Thermodynamic activation parameters for the pseudorotation process have been evaluated from the observed temperature variation of the parameters of the1H NMR spectrum. 2. The enol acetate of β-neopentylglycolphosphonepropionic aldehyde has been prepared. © 1978 Plenum Publishing Corporation

Terpinolene monoxide and dioxide and isomerization of the monoxide under the influence of zinc bromide

1. We synthesized terpinolene monoxide (4,8-epoxy-p-menthene-1) and dioxide for the first time and confirmed their structure from their NMR and IR spectra. 2. The isomerization of 4,8-epoxy-p-menthene-1 under the influence of zinc bromide was studied. Two isomeric ketones with the composition C10H16O were isolated in individual form; analysis of their PMR spectra provided a basis for assigning them a seven-member ring structure. © 1971 Consultants Bureau

Calculation of nuclear magnetic shielding constants by the method of gauge-invariant atomic orbitals using Gaussian functions

It has been shown that the using of the gauge-invariant atomic orbitals together with Gaussian expansion of orbitals allows one to obtain satisfactory results for the proton magnetic shielding constants without an average excitation energy approach, the wave functions being obtained by any MO LCAO method. It is necessary to employ a more complicated variation function for the calculations of 13C shielding constants. The proton and 13C shielding constants have been calculated for a number of molecules (CH4, C2H6, CH3NH2, CH3OH, CH3F). The simple functions, obtained by extended Hückel and INDO methods have been used as unperturbed solutions. Comparison with ab initio calculations and experimental data have been carried out. © 1979

1H and31P NMR study of the structure of 2-R-4-methyl-6,6-diphenyl-1-phospha-2,3-diazabicyclo [3.1.0]hex-3-ene and 2,3,4,5-tetrahydro-1,2,3-diazaphosphorine derivatives

1. The reaction of 2-R-5-methyl-1,2,3-diazaphospholeswith diphenyldtazomethane leads to the formation of 2-R-4-methyl-6,6-diphenyl-1-phospha-2,3-diazabicyclo[3.1.0]hex-3-enes which, upon heating with alcohols and reaction with dry HCl, convert to derivatives of 2,3,4,5-tetrahydro-1,2-diaza-3-phosphorines. 2. The stereochemical dependence of the3JP(III)CCH vicinal coupling constant on the dihedral angle for these phosphorines indicated predominant half-chair conformation with pseudoequatorial orientation of the phosphorus unshared electron pair orbital. © 1983 Plenum Publishing Corporation