期刊
JOURNAL OF PHYSICAL CHEMISTRY A
卷 116, 期 46, 页码 11370-11387出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp305863n
关键词
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资金
- Deutsche Forschungsgemeinschaft
- Fonds der Chemischen Industrie, Frankfurt
- Russian Foundation of Basic Research [11-03-00346]
We have studied the hydrogen bond interactions of N-15 labeled 4-methylpyridine (4-MP)with pentachlorophenol (PCP) in the solid state and in polar solution Using various NMR techniques. Previous spectroscopic, X-ray, and neutron crystallographic studies showed that the triclinic 1:1 complex (4-MPPCP) exhibits the strongest known intermolecular. OHN hydrogen bond in the solid state. By contrast, deuteration of the hydrogen bond gives rise to the formation of a monoclinic structure exhibiting a weaker hydrogen bond. By performing NMR experiments at different deuterium fractions and taking advantage of dipolar H-1-N-15 recoupling under combined fast MAS and H-1 decoupling, we provide an explanation of the origin of the isotopic polymorphism of 4-MPPCP and improve previous chemical shift correlations for OHN hydrogen bonds. Because of anharmonic ground state vibrations, an ODN hydrogen bond in the triclinic form exhibits a shorter oxygen-hydron and a longer oxygen-nitrogen distance as compared to surrounding OHN hydrogen bonds, which also implies a reduction of the local dipole moment. The dipole-dipole interaction between adjacent coupled OHN hydrogen bonds which determines the structure of triclinic 4-MPPCP is then reduced by deuteration, and other interactions become dominant, leading to the monoclinic form. Finally, the observation of stronger OHN hydrogen bonds by H-1 NMR in polar solution as compared to the solid state is discussed.
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