ISSN:
0749-1581
Keywords:
NMR
;
1H NMR
;
13CNMR
;
Dynamic NMR
;
β-Hydroxyphosphonates
;
Restricted rotation
;
Steric effects
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Free energies of activation, ΔG298≠, for the rotation of the phenyl group in the range of 46.06-63.25 kJ mol-1 were observed in some model β-hydroxyphosphonates. These barriers were found to depend on the type of substituents at the phosphorus atom and on the substituents at the β-position with respect to the phenyl ring. The steric origin of this observation is discussed. Dynamic NMR studies were performed in order to determine the activation parameters for the exchange process. For that purpose, variable-temperature 1H and 13C NMR spectra were treated by non-iterative, iterative and iterative double-fit procedures. MNDO, AM1 and PM3 theoretical calculations of the barriers for three of the compounds studied are reported and results are compared with the experiments. It is found that the PM3 results are very close to the experimental data.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260321102
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