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

Molecules

Pantelis Charisiadis¹  Vassiliki G. Kontogianni¹  Constantinos G. Tsiafoulis²  Andreas G. Tzakos¹  Michael Siskos¹ 

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

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

DOI  :  10.3390/molecules190913643

来源: mdpi

【 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 (Δν_1/2 ≤ 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 effects on –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】

CC BY   
© 2014 by the authors; licensee MDPI, Basel, Switzerland.