ISSN:
0749-1581
Keywords:
Karplus equation
;
Vicinal H/H coupling constant
;
Solvent effect
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A recently reported modified Karplus equation often produces large errors exceeding 1 Hz in the calculated vicinal H/H coupling constants [3J(H, H)], in spite of the high claimed accuracy of 0.33 Hz in the standard deviation. Critical examination of the equation against a large body of experimental 3J(H,H) values identified the following sources of errors: inaccurate proton positions in three- and four-membered rings, effects of polar solvents, especially on vicinal polyhalogenated compounds, conformer distributions obtained by inadequate computational methods and varying conditions for NMR measurements. When these are taken in to account the accuracy of the equation can be considered to have a standared deviation of 0.69 Hz. A small set of 3J(H,H) data calculated by the re-parameterized extended Hückel theory could be fitted well to a shortened form of the modified Karplus equation. This result suggests that a set of coupling constants derived by theoretical calculations may offer a better standard set for the study of the modification of the Karplus equation.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260301114
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