Additive NMR chemical shift parameters for deshielded methine protons

✍ Scribed by Harold M. Bell; Deborah B. Bowles; Fred Senese

• Book ID: 102950880
• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 501 KB
• Volume: 16
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270160407

✦ Synopsis

Abstract

The use of additive parameters for the prediction of NMR chemical shifts is widely practised. However, no correlations are available for highly deshielded methine protons. In this work, methine chemical shifts have been studied using both multiple linear regression analysis and Simplex function minimization in an effort to determine under what limiting circumstances the additivity of shift parameters can be expected to apply. As expected, it was not possible to explain satisfactorily all methine shifts with a single set of substituent parameters. However, if only the deshielded cases were considered (H—CXYZ, where at least two of the three groups X, Y, and Z are electron‐withdrawing), a much better set of parameters could be determined. Using a data set of 440 of these deshielded methine shifts, involving 31 different substituents, a standard error of estimate of 0.20 ppm is found for protons spread between 3.0 and 7.5 ppm.