Anisotropies and Absolute Signs of the Indirect Spin–Spin Coupling Constants in 13CH3F
| Autor: | R. A. Bernheim, T. R. Krugh |
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| Rok vydání: | 1970 |
| Předmět: | |
| Zdroj: | The Journal of Chemical Physics. 52:4942-4949 |
| ISSN: | 1089-7690 0021-9606 |
| DOI: | 10.1063/1.1672729 |
| Popis: | Proton and 19F magnetic resonance experiments on 13CH3F partially oriented in the liquid crystal solvent p,p′‐di‐n‐hexyloxyazoxybenzene show conclusively that JCH = + 148.8 ± 0.4 Hz, JCF = − 161.9 ± 0.7 Hz, and JHF = + 46.3 ± 0.3 Hz, with the signs absolutely determined. Assuming that there is no change of molecular geometry between the gas phase and the nematic solution, and neglecting solvent effects, isotope effects and corrections due to vibrational averaging, the experimental results suggest unexpectedly large anisotropies of the spin couplings, (J‖ − J⊥)CH = + 1890 Hz, (J‖ − J⊥)CF = + 700 Hz (measured with respect to the molecular symmetry axis), whereas JHF has negligible anisotropy. The anisotropies in Jij are examined with respect to their sensitivities upon the appropriate average molecular geometries used in their determination, and the effects of solvent are also discussed. The accuracy of the above anisotropies cannot be determined without a knowledge of the complete vibrational potential of methylfluoride. However, it can be concluded that indirect spin coupling anisotropies do exist for directly bonded nuclei, and that at least one of them is sizeable, of the order of magnitude of the isotropic Jij. |
| Databáze: | OpenAIRE |
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