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Critical evaluation of an empirically modified Karplus equation
Author(s) -
Ōsawa Eiji,
Ouchi Tatsuro,
Saito Nobuhisa,
Yamato Masaru,
Lee Oh Seuk,
Seo MiKyo
Publication year - 1992
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260301114
Subject(s) - vicinal , chemistry , parameterized complexity , coupling constant , standard deviation , set (abstract data type) , proton , conformational isomerism , computational chemistry , thermodynamics , molecule , quantum mechanics , statistics , mathematics , physics , algorithm , organic chemistry , computer science , programming language
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.