Pranab K. Bhattacharyya

15N magnetic shielding anisotropies in 15N15NO

The 15N magnetic shielding anisotropies in nitrous oxide (15N15NO) have been determined using a pulsed FT NMR spectrometer. The shielding anisotropies obtained from the temperature dependence of the nematic phase chemical shifts are 512 ± 10 ppm (central 15N) and 369 ± 15 ppm (end 15N). The values obtained from the nematic‐isotropic phase difference method are 505 ± 10 ppm (central 15N) and 366 ± 10 ppm (end 15N). Theoretical estimates of the anisotropies from the so‐called atom dipole method are also reported. The indirect scalar coupling constant has been assigned to be negative. The signs of the 15N spin‐rotation constants are predicted to be positive.

Anisotropies in carbon-13 chemical shift tensor, H-C-H bond angles and the signs of the coupling constants in 13CH3I, 13CH3Br, 13CH3Cl

A pulsed fast Fourier transform N.M.R. spectrometer is used to investigate the temperature dependence of the 13C chemical shifts in the nematic liquid crystal solutions of the following halides: 13CH3I, 13CH3Br, 13CH3Cl. The H-C-H bond angles are accurately measured in this investigation from proton magnetic resonance studies. The signs of the coupling constants D 13CH , D HH, J 13CH and the ordering parameter have been assigned to be all positive. The 13C magnetic shielding anisotropy is found to become more positive with the increasing electronegativity of the halogen substituents. The values of the anisotropies are: Δσ = σ ∥ - σ ⊥ = - 101 ± 15 p.p.m. (13CH3I), - 10 ± 5 p.p.m. (13CH3Br), 22 ± 5 p.p.m. (13CH3Cl). Results for Δσ obtained from the slope of σn versus S 33 agree with those obtained from the nematic-isotropic phase subtraction method.

19F and 31P magnetic shielding anisotropies in phosphoryl fluoride

The 19F and 31P magnetic shielding anisotropies in the phosphoryl fluoride molecule have been determined from studies of the temperature dependence of the 19F and 31P chemical shifts and the anisotropic couplings in nematic solutions. Measurements of the F-P-F bond angle are reported. The possible existence of an anisotropy in the indirect P-F spin-spin coupling which is investigated does not change the values of the shielding anisotropies significantly.

13C and 1H chemical-shift anisotropies in chloroform

Abstract The anisotropies in the 13 C and 1 H chemical-shift tensors in chloroform are determined using a pulsed FT NMR spectrometer. The 13 C shielding anisotropy, obtained from the temperature dependence of the nematic-phase carbon-13 chemical shift and the ordering parameter, is —39 ± 1 ppm. A similar value is also obtained from the nematic-isotropic phase difference method. The value of 1 H shielding anisotropy obtained from temperature studies in the nematic phase is 9.8 ± 2.5 ppm.

Structural parameters and the 13C and 19F magnetic shielding anisotropies in 13CH3F from nematic phase studies

Abstract The HCH bond angle and the ratios of internuclear distances in methyl fluoride are determined from 1 H- and 13 C-NMR studies of the spectral splittings. The value of the HCH bond angle is found to be sensitive to the particular nematic solvent used. The 13 C shielding anisotropy in this molecule is determined in three different liquid crystal solvents and the average value is σ | − σ | = 66 ± 15 ppm. The 19 F isotropic shift in methyl fluoride increases linearly with temperature in both the nematic and isotropic phases. Hence, it is necessary to consider this linear temperature dependence in the evaluation of the correct value for the 19 F shielding anisotropy. The value of the 19 F shielding anisotropy in methyl fluoride has been determined to be −73 ± 10 ppm from nematic phase studies. The nematic-isotropic phase subtraction method for obtaining fluorine anisotropy yields an incorrect value because of the discontinuity in the isotropic shift in methyl fluoride at the transition point.

Deuteron quadrupole coupling constants in CD3F and 1,3,5‐C6D3F3

The deuteron quadrupole coupling constants in the deuterated methyl fluoride and 1,3,5‐trifluorobenzene molecules have been determined from nematic phase studies using a pulsed FT NMR spectrometer. The values obtained in the molecular symmetry axis system are as follows: χzz = −47.8±1.5 kHz (in CD3F) and χzz = −94.4±0.7 kHz (in 1,3,5‐C6D3F3). If the field gradient tensor is assumed to be diagonal in the C–D bond axis system, the values of the coupling constants referred to the C–D bond are given by χCD = 133±7 kHz (in CD3F, η = 0.03±0.03) and χCD = 180±3 kHz (in 1,3,5‐C6D3F3, η = 0.05±0.01).

Carbon-13 magnetic shielding anisotropy in acetonitrile-1-13C obtained from NMR studies in a liquid crystal solution

Abstract The carbon-13 magnetic shielding anisotropy in acetonitrile-1- 13 C has been obtained from studies in a liquid crystal solution using a pulsed FT NMR spectrometer. The value obtained, for σ 8 - σ ⊥ , is 302 ± 8 ppm. The HCH bond angle in acetonitrile is determined to be 109° 18′ ± 2′. The sign of J C(C)H is found to be negative in accordance with the double resonance experimental result. The spin-rotation constants of the nitrile carbon nucleus have been estimated from the atom dipole method.

13C chemical shift anisotorpy and the H–C–H bond angle of 13CH3 OH in a nematic liquid crystal solvent

A pulsed FT NMR spectrometer is used to determine the anisotropy in the carbon‐13 chemical shift tensor and the H–C–H bond angle in methyl alcohol from studies in a nematic liquid crystal solvent. The H–C–H bond angle measured by proton magnetic resonance is 109 ° 20′ ± 4′. The signs of the coupling constants D13CH, DHH, and J13CH and the ordering parameter S33 are established to be all positive. The value of Δσ (13C) obtained from temperature studies of the nematic phase chemical shift is 69 ± 5 ppm. The anisotropy obtained from the nematic—isotropic phase chemical shift difference (at 77 °C) is 63 ± 6 ppm.

Molecular Magnetic Susceptibility Tensor in Sulfur Dioxide

The diagonal elements in the magnetic susceptibility tensor in the principal molecule‐fixed inertial axis system in SO2 have been determined by observing the molecular rotational Zeeman effect with a high‐resolution microwave spectrometer. The signs of gaa, gbb, gcc have been found to be negative from theroetical considerations. The principal values of the magnetic susceptibility tensor, paramagnetic susceptibility tensor, and diamagnetic susceptibility tensor are, respectively: χaa = − 14.4 ± 1.2, χbb = − 19.6 ± 0.5, χcc = − 20.6 ± 0.6; χaap = 38.9 ± 0.3, χbbp = 129.3 ± 1.4, χccp = 139.5 ± 1.2; χaad = − 53.3 ± 1.2, χbbd = − 148.9 ± 1.5, χccd = − 160.1 ± 1.3 (all in units of 10−6 erg/G2·mole). The ground‐state averages of the sum of the squares of the electronic coordinates, and approximate values of the diagonal components of the quadrupole moment tensor have also been determined.The diagonal elements in the magnetic susceptibility tensor in the principal molecule‐fixed inertial axis system in SO2 have been determined by observing the molecular rotational Zeeman effect with a high‐resolution microwave spectrometer. The signs of gaa, gbb, gcc have been found to be negative from theroetical considerations. The principal values of the magnetic susceptibility tensor, paramagnetic susceptibility tensor, and diamagnetic susceptibility tensor are, respectively: χaa = − 14.4 ± 1.2, χbb = − 19.6 ± 0.5, χcc = − 20.6 ± 0.6; χaap = 38.9 ± 0.3, χbbp = 129.3 ± 1.4, χccp = 139.5 ± 1.2; χaad = − 53.3 ± 1.2, χbbd = − 148.9 ± 1.5, χccd = − 160.1 ± 1.3 (all in units of 10−6 erg/G2·mole). The ground‐state averages of the sum of the squares of the electronic coordinates, and approximate values of the diagonal components of the quadrupole moment tensor have also been determined.

High resolution microwave studies of the magnetic properties of OCS

Abstract A high resolution Zeeman microwave spectrometer employing a superconducing magnet, superheterodyne detection, and a microwave resonant cavity absorption cell was used to accurately measure the rotational magnetic moment and molecular magnetic susceptibility anisotropy of 16 O 12 C 32 S. Δ M J = ±1 Zeeman transitions of the J = 1 → 2 rotational absorption line were studied, yielding the following results: g 1 = −0.028860 ± 0.000037, g 2 = −0.028870 ± 0.000037, Δ x = (−9.36 3 ± 0.01 6 ) × 10 −6 emu/mole. From these data the molecular quadrupole moment of 16 O 12 C 32 S has been evaluated as O | = (−0.773 ± 0.023) × 10 −26 esu cm 2 .