ISSN:
0749-1581
Keywords:
NMR 17O NMR
;
Phenols
;
Salicylaldehydes
;
Hydrogen bonding
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Natural abundance 17O NMR data for fifteen 2- and 4-substituted phenols, ten 3-and 5-substituted 2-hydroxybenzaldehydes and eight 3-substituted benzaldehydes, recorded at 75°C in acetonitrile are reported. The chemical shift change due to intramolecular hydrogen bonding for the phenolic oxygen was found to be 10-14 ppm shielding. In acetonitrile, the 17O NMR chemical shift for phenol signals was insensitive to added water up to water concentrations of 0.5 mole fraction. The 17O NMR chemical shifts of the 4-substituted phenols gave an excellent correlation (r = 0.990) with anisole 17O NMR data; the data also correlated moderately well with σ- (r = 0.974). The chemical shifts of the 3-substituted benzaldehydes were correlated with σ+ values (r = 0.991). A plot of the carbonyl chemical shift data for the substituted 2-hydroxybenzaldehydes versus the carbonyl data for 3-substituted benzaldehydes gave a slope of 0.87 and with r = 0.960. The plot of the 4-substituted phenol data with that for OH of the corresponding 2-hydroxybenzaldehydes gave a slope of 1.04 with r = 0.996. Proton to oxygen coupling for the phenolic group of several of the intramolecular hydrogen bonded systems was observed directly [J(OH) = 58-92 Hz]. MM2 and MOPAC calculations predict that the hydrogen bond distances and angles for the substituted 2-hydroxybenzaldehydes and the partial atomic charges for the carbonyl groups (AMI) were essentially constant. After corrections for electronic effects the chemical shift changes due to hydrogen bonding for the donor (ΔδHBD) and acceptor (ΔδHBA) of the carbonyl-phenol intramolecular bonding system were 5-12 and 30 ± 2 ppm, respectively. The ΔδHBA value was between those for keto and ester acceptors consistent with the relative basicity of the aldehyde group. The ΔδHBD value was substantially larger than those for phenolic donors to keto and ester groups.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260310513
Permalink
