1H-NMR as a Structural and Analytical Tool of Intra- andIntermolecular Hydrogen Bonds of Phenol-Containing Natural Products and Model Compounds

Molecules

Constantinos G. Tsiafoulis¹  Michael Siskos²  Vassiliki G. Kontogianni²  Pantelis Charisiadis²  Ioannis P. Gerothanassis²  Andreas G. Tzakos² 

[1] NMR Center, University of Ioannina, Ioannina GR-45110, Greece;Section of Organic Chemistry & Biochemistry, Department of Chemistry, University of Ioannina, Ioannina GR-45110, Greece;

关键词: chemical shifts;    hydrogen bonding;    1H-NMR;    1H-13C HMBC;    phenol OH;    natural products;   

DOI  :  10.3390/molecules190913643

来源: DOAJ

【 摘 要 】

Experimental parameters that influence the resolution of 1H-NMR phenol OH signals are critically evaluated with emphasis on the effects of pH, temperature and nature of the solvents. Extremely sharp peaks (Δν1/2 ≤ 2 Hz) can be obtained under optimized experimental conditions which allow the application of 1H-13C HMBC-NMR experiments to reveal long range coupling constants of hydroxyl protons and, thus, to provide unequivocal assignment of the OH signals even in cases of complex polyphenol natural products. Intramolecular and intermolecular hydrogen bonds have a very significant effect on 1H OH chemical shifts which cover a region from 4.5 up to 19 ppm. Solvent effectson –OH proton chemical shifts, temperature coefficients (Δδ/ΔT), OH diffusion coefficients, and nJ(13C, O1H) coupling constants are evaluated as indicators of hydrogen bonding and solvation state of phenol –OH groups. Accurate 1H chemical shifts of the OH groups can be calculated using a combination of DFT and discrete solute-solvent hydrogen bond interaction at relatively inexpensive levels of theory, namely, DFT/B3LYP/6-311++G(2d,p). Excellent correlations between experimental 1H chemical shifts and those calculated at the ab initio level can provide a method of primary interest in order to obtain structural and conformational description of solute-solvent interactions at a molecular level. The use of the high resolution phenol hydroxyl group 1H-NMR spectral region provides a general method for the analysis of complex plant extracts without the need for the isolation of the individual components.

【 授权许可】

Unknown