ISSN:
0749-1581
Keywords:
Nitroxides
;
Nitrogen isotropic coupling constants
;
Solvent polarity
;
ESR spectra
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The dependence of the nitrogen isotropic coupling constants, aN, on the structure and charge of the radicals, temperature and solvent polarity was analysed for solutions containing the following nitroxides: 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol); 4-trimethylammonium-2,2,6,6-tetramethylpiperidine-1-oxyl, iodide salt (TempTMA+); 2,2,5,5-tetramethylpyrrolin-1-oxyl-3-carboxamide (Tempyo); and 2,2,5,5-tetramethylpyrrolin-1-oxyl-3-carboxylate, sodium salt (Tempyca-). Polar hydrogen bond acceptor solvents and hydroxylic solvents were used. In each solvent used, Tempol and Tempyca- showed aN values which were higher, respectively, than those of TempTMA+ and Tempyo due to inductive, structural and charge effects. Such effects were analysed on the basis of the proton and 13C coupling constants. Non-hydroxylic solvents gave temperature coefficients for aN that were almost independent of solvent polarity. Lower daN/dT values were found for charged radicals. A gradual decrease of temperature coefficients with decreasing hydrogen bond donor (HBD) properties were related to free volume changes of radical molecules. The analysis of the aN dependence on polarity parameters gave the best fitting using a simplified form of the Wertheim reaction field. Tempyca- was greatly affected by changes in polarity. A parameter to account for HBD abilities was also analysed.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260251014
Permalink
