William M. Litchman

Proton exchange and temperature studies of pyrazole in dimethyl-d/sub 6/ sulfoxide by /sup 13/C NMR

The /sup 13/C NMR shifts of all the carbons in pyrazole have been observed at room temperature. This paper reports the kinetic data available from the temperature-induced collapse of the C-3, C-5 NMR peaks. ..delta..G/sup 2 +/ similarly ordered 7.0 kcal/mol, and ..delta..S/sup 2 +/ similarly ordered -25.0 cal/deg for the virtual tautomerism of pyrazole in SO-d/sub 6/. Temperature-induced /sup 13/C DM shofts for the solvent and for pyrazole were also determined to be +1.47 x 10/sup -3/ and +2.0 x 10/sup -3/ ppM/deg for C-4 and the center of the C-3, C-5 peaks, respectively. The solvent shift for /sup 13/C with temperature is +11.59 +- 10/sup -3/ ppM/deg for the CD/sub 3/ in DM SO-d/sub 6/ and +3.22 x 10/sup -3/ ppM/deg for the deuterium in Me/sub 2/SO-d/sub 6/. Rapid exchange of pyrazole observed earlier by several workers in the solvent Me/sub 2/SO-d/sub 6/ is attributed to acid impurities present in previous samples. 3 tables.

Heteronuclear double resonance: Theoretical description of intensity effects in A(X2) and A(X3) systems

Abstract The line intensities in an A(X n ) double-resonance spectrum appear anomalous, sometimes even with transitions in emission. These intensities are the result of the population distribution among the levels of the effective double-resonance Hamiltonian in rotating axes. Two factors determine these populations: the tilt effect (the result of the tilting of the effective field in the rotating axis) and the relaxation effect. These effects are demonstrated for various examples and it is shown how different relaxation mechanisms alter the line intensities.

15N Spin Lattice Relaxation in Liquid 15NH3 and 15ND3

The spin‐lattice relaxation times (T1) for 15N in 15NH3 and 14ND3 have been determined and are presented and discussed. The magnitudes and temperature dependences of T1 for 15NH3 and 15ND3 indicate that spin‐rotational and intramolecular dipolar interactions together dominate the 15N relaxation in 15NH3. Since γD≈ 0.15 γH, the dipolar term is small compared with the spin‐rotational term in 15ND3 at room temperature. This allows one to separate the spin‐rotational and dipolar contributions in 15NH3. Values of τc, τsr, and CN are then derived from the experimental data for 15NH3 and compared with values derived in other work.

A study of the interactions of pyridine in solution by means of 13C NMR

Abstract The 13 C solvent shifts of pyridine in 14 solvents are reported. The infinite dilution shift (extrapolated from the dilution curve) is related to similar work on solvent shifts reported previously for nitrogen-15 in trimethylamine. The effects of solvents on the pyridine carbon chemical shifts are shown to be related to functional groups present in the solvent molecule.

Density and Viscosity of Liquid ND3

The density and viscosity of liquid ND3 have been measured over the temperature range from +30° to −25° and compared with the density and viscosity of liquid NH3. At any given temperature, the ratio of densities ρND3/ρNH3 is 1.187± 0.001 and the ratio of viscosities ηND3/ηNH3 is 1.20± 0.01. The fact that both ratios are independent of temperature suggests that the strengths of intermolecular interactions are essentially the same in the two liquids and that the density and viscosity differences are to be attributed to differences in molecular size and mass. The density ratio indicates that the molecular volume of NH3 in the liquid is ∼ 1% larger than that of ND3 while the viscosity ratio indicates that the viscosity varies directly as M/Vm (Vm=molar volume) for these two liquids.

Temperature effects on the carbon-13 NMR shifts of selected compounds

Abstract The effects of temperature on the 13 C NMR shifts of benzene, cyclohexane, pyridine, cyclohexene, neopentane, hexane, and heptane have been determined from +10 to +70°C. In addition, the temperature shift of 2 D in D 2 O was found to be +10.4 × 10 −3 ppm/°C. All shifts appear to be linear functions of temperature within experimental error.

A calculation of nitrogen chemical shifts for the methyl amines and methylamine hydrochlorides

Abstract Using the Ramsey formulation of the chemical shift parameter and a VB formalism, the chemical shifts of the methyl amines and methylamine hydrochlorides have been calculated. In addition, pair-interaction terms in a linear expression are presented and discussed in the light of deviations from the classical VB structure. The chemical shift produced by the protonation of an amine in this series is shown to be the result of changes in the diamagnetic term. The paramagnetic term is discussed with regard to the value of the average excitation energy.

A 13C NMR study of two alpha-picolines

Abstract The structures of two previously unreported alpha-picolines are assigned by 13 C NMR and the spectral parameters for these two compounds are presented and discussed. Evidence for intramolecular hydrogen bonding is presented.