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17 O NMR spectroscopic study of substituted benzoquinones and α,β‐unsaturated cyclic ketones
Author(s) -
Boykin D. W.,
Baumstark A. L.,
Mehdizadeh A.,
Venkatramanan M. K.
Publication year - 1990
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260280405
Subject(s) - chemistry , quinone , enone , carbonyl group , acetonitrile , ring (chemistry) , shielding effect , van der waals force , medicinal chemistry , ketone , stereochemistry , group (periodic table) , electronic effect , molecule , organic chemistry , steric effects , layer (electronics)
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.