Influence of a Side-Chain on Deuterium Isotope Effects in 13C NMR Spectra of Some Benzene Derivatives

✍ Scribed by P. Novak; D. Vikić-Topić; Z. Meić; E. Gacs-Baitz

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 572 KB
• Volume: 34
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199608)34:8<610::aid-omr938>3.0.co;2-o

✦ Synopsis

Deuterium-induced isotope effects on 13C chemical shifts were measured in a series of benzene derivatives, viz. toluene, benzoic acid and benzophenone. The effects over two, three and four bonds reflect a dependence on the transmission pathway and the nature of the side-chain. Steric and inductive influences of side-chain lone pair electrons located at the fl-position to the phenyl ring account for a lower magnitude and negative sign of some effects in the deuteriated phenyl ring. In monodeuteriated benzophenones isotope effects are transmitted to the second phenyl ring, e.g. in p-deuteriobenzophenone over up to nine bonds. Although the carbonyl group allows only a minor conjugation between the phenyl rings, the extent, the magnitude and the sign of isotope effects resemble those in fully conjugated molecules, indicating a similar transmission mechanism. In polydeuteriated isotopomers, the additivity of isotope effects holds for the majority of carbon atoms. However, in few cases significant deviations exist owing to perturbations in hydrogen-bond dynamics and redistribution of rotamer populations caused by deuteriation. For monodeuteriated isotopomers, a number of 13C-'H coupling constants through one and three bonds are also reported. KEY WORDS 13C NMR; deuterium isotope effects; toluene; benzoic acid; benzophenone * Author to whom correspondence should be addressed t P. Novak was previously P. VujaniC. 3 2 d r ' 1 D 2 3 4 0 c & OH 0 & OH 0 c + OH 0 OH D Ds 5 6 1 8 0 0 0 D 9 to 11 0 II vcm D, 12 +p 13 Scheme 1