ISSN:
0749-1581
Keywords:
Lanthanide-induced shift
;
Conformational analysis
;
1H NMR
;
Complexation model
;
Norborneol
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The complete assignment of the proton chemical shifts for 2-exo-norboreol was obtained from a COSY experiment at 250 MHz. Using these assignments the conformation of this molecule in solution was studied using the lanthanide-induced shift technique, applying a new three-site lanthanide complexation model (LIRAS4) reflecting the coordination geometry at the hydroxyl oxygen atom.The substrate geometry which was found to give the best correlation between the calculated and observed shifts was not in agreement with the optimized geometry calculated using ab initio methods, the CCO angle being optimized as 108° in the former compared with 110.80° in the latter. The lanthanide complex geometry found indicated that one of the sites (trans to H-2n) was occupied by the hydroxyl proton with the shift reagent bound to two other sites. This was supported by the increase in the vicinal J(HCOH) coupling observed on addition of the shift reagent. This LIRAS4 solution was then refined using a more complex model, HARDER, which treats each site as being independent of each other. The final two-site solution obtained reflects the symmetry about the binding site in this molecule, and gave an excellent correlation between the observed and calculated shifts (Rx = 2.594, RR = 3.20 Å, PhiR = 105°, PsiR = 130°, RL = 3.00 Å, PhiL = 130°. PsiL = 130°).
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260261117
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