17O NMR spectroscopic study of substituted benzoquinones and α,β-unsaturated cyclic ketones

✍ Scribed by D. W. Boykin; A. L. Baumstark; A. Mehdizadeh; M. K. Venkatramanan

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 465 KB
• Volume: 28
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260280405

✦ Synopsis

Abstract

The ^17^O NMR chemical shift data for a series of substituted benzoquinones and α,β‐unsaturated cyclic ketones in acetonitrile at 75°C are reported. In general, for the unsymmetrically substituted quinones two signals were observed, the assignments of which were made by ^17^O enrichment and exchange experiments. For the benzoquinones, the effect of α‐methyl substitution (shielding) was greater on the signal for the 1‐carbonyl group than on that for the 4‐carbonyl group. α‐tert‐Butyl substitution resulted in deshielding of the proximate carbonyl group compared with that in the methyl analog. For the five‐ and six‐membered ring enones the shielding effect of β‐substituents was interpreted as electronic in origin. The large shielding effects observed for α‐substitution in the quinone and enone systems appeared to be the result of a combination of electronic and attractive van der Waals effects.