1989 Fiscal Year Final Research Report Summary
Gas-phase High Resolution NMR and its Application to Structural Chemistry
| Project/Area Number |
63470006
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
構造化学
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| Research Institution | University of Tokyo |
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Principal Investigator |
HIRANO Tsuneo Univ. of Tokyo, Dept. of Synthetic Chemistry Assoc. Prof., 工学部, 助教授 (40011027)
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| Co-Investigator(Kenkyū-buntansha) |
SATO Hisaya Tokyo Univ. of Agriculture and Technology, Dept. of Material System, Assoc. Prof, 工学部, 助教授 (90092486)
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| Project Period (FY) |
1988 – 1989
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| Keywords | gas-phase nmr / structural chemistry / unperturbed state / Gibbs free energy / 1,2-difluoroethane / gauche effect / conformational energy / ab initio |
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| Research Abstract |
Low pressure (0.01 - 0.5 atm) Gas-phase high-resolution NMR method is a useful tool for the structural study of unperturbed states, i.e. states free from solvent and intermolecular interactions. Their data can directly be compared with the predictions from quantum chemical and molecular mechanics calculations since these methods also calculate for a molecule in an isolated state.
In this study, we extended our novel method for the ^1H NMR to ^<19>F and ^<13>C NMR, and made some applications to the structural problems.
1) We have succeeded in developing new observation method for ^<19>F nucleus NMR, and was able to obtain NMR spectra of very high resolution.
2) Applying the variable temperature ^1H and ^<19>F gas-phase NMR methods to the investigation of "gauche-effect" in 1,2-difluoroethane, we determined enthalpy and entropy differences between gauche and trans conformers in the unperturbed states. The Gibbs free energy difference thus determined, DELTAG(G-T), is -0.81 kcal/mol, which is in good agreement with the value -0.85 kcal/mol from MP3/6-311++G^<**> ab initio calculations. The 1-4 through bond interaction between H and F atoms was found to play the most important role in the gauche-effect.
3)Taking methanol and dimethyl ether as examples, we succeeded in obtaining a well-resolved ^<13>C low pressure gas-phase NMR spectra at 270 MHz with 10 mm sample tube. Method of observation should further be improved for general applications, but it could become a useful tool for the structural chemistry in the unperturbed state.
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