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1H chemical shifts in NMR: Part 22—Prediction of the1H chemical shifts of alcohols, diols and inositols in solution, a conformational and solvation investigation

2005; Wiley; Volume: 43; Issue: 8 Linguagem: Inglês

10.1002/mrc.1611

1097-458X

Raymond J. Abraham, Jonathan J. Byrne, Lee Griffiths, Rodothea Koniotou,

Cassava research and cyanide

The 1H NMR spectra of a number of alcohols, diols and inositols are reported and assigned in CDCl3, D2O and DMSO-d6 (henceforth DMSO) solutions. These data were used to investigate the effects of the OH group on the 1H chemical shifts in these molecules and also the effect of changing the solvent. Inspection of the 1H chemical shifts of those alcohols which were soluble in both CDCl3 and D2O shows that there is no difference in the chemical shifts in the two solvents, provided that the molecules exist in the same conformation in the two solvents. In contrast, DMSO gives rise to significant and specific solvation shifts. The 1H chemical shifts of these compounds in the three solvents were analysed using the CHARGE model. This model incorporates the electric field, magnetic anisotropy and steric effects of the functional group for long-range protons together with functions for the calculation of the two- and three-bond effects. The long-range effect of the OH group was quantitatively explained without the inclusion of either the CO bond anisotropy or the COH electric field. Differential β and γ effects for the 1,2-diol group needed to be included to obtain accurate chemical shift predictions. For DMSO solution the differential solvent shifts were calculated in CHARGE on the basis of a similar model, incorporating two-bond, three-bond and long-range effects. The analyses of the 1H spectra of the inositols and their derivatives in D2O and DMSO solution also gave the ring 1H,1H coupling constants and for DMSO solution the CHOH couplings and OH chemical shifts. The 1H,1H coupling constants were calculated in the CHARGE program by an extension of the cos2ϕ equation to include the orientation effects of electronegative atoms and the CHOH couplings by a simple cos2ϕ equation. Comparison of the observed and calculated couplings confirmed the proposed conformations of myo-inositol, chiro-inositol, quebrachitol and allo-inositol. The OH chemical shifts were also calculated in the CHARGE program. Comparison of the observed and calculated OH chemical shifts and CH.OH couplings suggested the existence of intramolecular hydrogen bonding in a myo-inositol derivative. Copyright © 2005 John Wiley & Sons, Ltd.