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Experimental and theoretical study of the methoxy group conformational effect on 13C chemical shifts in ortho-substituted anisoles

✍ Scribed by Rodolfo R. Biekofsky; Alicia B. Pomilio; Ruben H. Econteras; Dora G. de Kowalewski; Julio C. Facelli

Publisher
John Wiley and Sons
Year
1989
Tongue
English
Weight
398 KB
Volume
27
Category
Article
ISSN
0749-1581

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✦ Synopsis

Aromatic I3C chemical shifts are reported for a number of ortho-substituted anisoles. Quantitative determination of the substituent chemical shift (SCS) effects of the methoxy group with a fixed coplanar conformation on aryl carbon nuclei was achieved using experimental and theoretical methods. The experimental values were compared with those calculated through the use of the additivity, and a systematic departure from additivity was found for carbon nuclei in ortho positions. Ortho-SCSs were found to be non-equivalent, and the ortho effect on the carbon cis to the fixed metboxy moiety was more shielding than in anisole. The IGLO (Individual Gauge for Localized Orbitals) method was used to calculate the SCSs. Experimental and theoretical trends obtained for the influence of the side-chain conformations on chemical shifts are in very good agreement with each other, and with recent results obtained by solid-state NMR. KEY WORDS orthosubstituted anisoles Substituent chemical shifts I3C NMR Methoxy group conformational effect ~~ ~

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