✦ LIBER ✦

Critical evaluation of an empirically modified Karplus equation

✍ Scribed by Eiji Ōsawa; Tatsuro Ouchi; Nobuhisa Saito; Masaru Yamato; Oh Seuk Lee; Mi-Kyo Seo

Publisher: John Wiley and Sons
Year: 1992
Tongue: English
Weight: 445 KB
Volume: 30
Category: Article
ISSN: 0749-1581
DOI: 10.1002/mrc.1260301114

No coin nor oath required. For personal study only.

✦ Synopsis

Abstract

A recently reported modified Karplus equation often produces large errors exceeding 1 Hz in the calculated vicinal H/H coupling constants [^3^J(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 ^3^J(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 ^3^J(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.

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