An NMR, IR and theoretical investigation of 1H Chemical Shifts and hydrogen bonding in phenols

Abraham, Raymond J. and Mobli, Mehdi (2007) An NMR, IR and theoretical investigation of 1H Chemical Shifts and hydrogen bonding in phenols. Magnetic resonance in chemistry, 45 10: 865-877. doi:10.1002/mrc.2060


Author Abraham, Raymond J.
Mobli, Mehdi
Title An NMR, IR and theoretical investigation of 1H Chemical Shifts and hydrogen bonding in phenols
Formatted title
An NMR, IR and theoretical investigation of 1H Chemical Shifts and hydrogen bonding in phenols
Journal name Magnetic resonance in chemistry   Check publisher's open access policy
ISSN 1097-458X
0749-1581
Publication date 2007-10
Sub-type Article (original research)
DOI 10.1002/mrc.2060
Volume 45
Issue 10
Start page 865
End page 877
Total pages 13
Place of publication Chichester
Publisher J. Wiley
Language eng
Subject 060112 Structural Biology (incl. Macromolecular Modelling)
Formatted abstract
The change in 1H NMR chemical shifts upon hydrogen bonding was investigated using both experimental and theoretical methods. The 1H NMR spectra of a number of phenols were recorded in CDCl3 and DMSO solvents. For phenol, 2- and 4-cyanophenol and 2-nitrophenol the OH chemical shifts were measured as a function of concentration in CDCl3. The plots were all linear with concentration, the gradients varying from 0.940 (phenol) to 7.85 (4-cyanophenol) ppm/M because of competing inter- and intramolecular hydrogen bonding. Ab initio calculations of a model acetone/phenol system showed that the OH shielding was linear with the HOC distance (R) for R < 2.1 Å with a shielding coefficient of - 7.8 ppm/Å and proportional to cos2 where is the HOCC dihedral angle. Other geometrical parameters had little effect. It was also found that the nuclear shielding profile is unrelated to the hydrogen bonding energy profile. The dependence of the OH chemical shift on the density on the oxygen atom was determined as ca 40 ppm/ electron. This factor is similar to that for NH but four times the value for sp2 hybridized carbon atoms. The introduction of these effects into the CHARGE programme allowed the calculation of the 1H chemical shifts of the compounds studied. The CHARGE calculations were compared with those from the ACD database and from GIAO calculations. The CHARGE calculations were more accurate than other calculations both when all the shifts were considered and also when the OH shifts were excluded. The calculations from the ACD and GIAO approaches were reasonable when the OH shifts were excluded but not as good when all the shifts were considered. The poor treatment of the OH shifts in the GIAO calculations is very likely due to the lack of explicit solvent effects in these calculations
Keyword NMR
1H
chemical shifts
phenols
IR
CHARGE
GIAO
DFT
hydrogen bonding
Q-Index Code C1
Additional Notes This is part 25 of 1H Chemical Shifts in NMR series

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
Institute for Molecular Bioscience - Publications
 
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