Substituent chemical shift correlations. Hammett σp+ values and shifts for exocyclic protons in para-substituted benzene derivatives

✍ Scribed by Brian Maurice Lynch

• Publisher: John Wiley and Sons
• Year: 1974
• Tongue: English
• Weight: 276 KB
• Volume: 6
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270060313

✦ Synopsis

Abstract

The methyl ^1^H NMR shifts for series of para‐substituted N,N‐dimethylanilines as their conjugate acids in trifluoroacetic acid, and series of para‐substituted N,N,N‐trimethylphenyl‐ammonium iodides in acetonitrile and in deuterium oxide, and the methylene shifts for series of para‐substituted N,N‐diethylanilines as their conjugate acids in deuteriosulfuric acid, are shown to be linearly related to the Hammett σ~p~+ parameter. It is proposed that this dependence reflects a response of the chemical shift of the proton of the probe moiety to the electron density at the point of attachment of the probe to the aromatic ring and that this response is determined by the electric field effect of the charge at the point of attachment. Literature data are cited to indicate that Hammett σ~p~+–^1^H NMR shift relationships may be general for probe moieties lacking a through‐resonance mechanism for interaction between the probe and the aromatic ring.