The role of aromatic groups in the Tobey–Simon additivity rule for vinylic protons

✍ Scribed by Henry J. Shine; Paramashivappa Rangappa

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 171 KB
• Volume: 45
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.2089

✦ Synopsis

Abstract

The Tobey–Simon (additivity) rule for aromatic groups which was devised about 40 years ago has been found to need revision. The rule shows an aromatic group attached to a CC double bond as causing a downfield chemical shift of a cis‐related vinylic proton and a small upfield shift of a trans‐related proton. A search of data in the recent literature has shown that this rule should apply mainly to monosubstituted phenyl groups and some polynuclear aromatics. In contrast with them, 2,6‐disubstituted phenyl, 2,4,6‐trisubstituted phenyl and 9‐anthracenyl groups cause cis‐related vinylic protons to resonate upfield of comparable trans‐related protons. Further, the current rule for o‐substituted phenyl groups has been found to be inaccurate. In writing a rule for aromatic groups, therefore, greater attention needs to be given to the diversity of effects that these groups have on chemical shifts of vinylic protons. Copyright © 2007 John Wiley & Sons, Ltd.