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

Abstract

The "0 NMR chemical shift data for a series of substituted benzoquinones and a,/?-unsaturated cyclic ketones in acetonitrile at 75 O C are reported. In general, for the unsymmetrically substituted quinones two signals were observed, the assignments of which were made by "0 enrichment and exchange experiments. For the benzoquinones, the effect of a-methyl substitution (shielding) was greater on the signal for the l-carbonyl group than on that for the karbonyl group. a-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 /?-substituents was interpreted as electronic in origin. The large shielding effects observed for a-substitution in the quinone and enone systems appeared to be the result of a combination of electronic and attractive van der Waals effects.

Hydrogen-Bonding in Cyclic 2-(3-Oxo-3-phenylpropyl)-Substituted 1,3-Diketones: 17O-NMR Spectra and X-Ray Structure Determination

“…The CO signal of the five-membered-ring enone 1c is shielded by 38 ppm compared with that of the six-membered-ring enone 1a. The difference is similar to that of cyclic enones (Dd % 36 ± 42 ppm) [13], and larger than that observed for cyclic 2-(phenylmethylene) ketones (Dd 28 ppm) [14], cyclic 2-(N,N-dimethylmethylene) ketones (Dd 22 ± 25 ppm) and saturated cyclic ketones (Dd 13 ppm) [12]. The additional Me group at C(2) of these compounds, as in 2a and 2c, causes a slight shielding of the TMSO O-atom (4 ± 7 ppm), indicating that the conjugation of the OÀCCÀCO system is reduced due to the steric interactions between the Me and the TMSO groups and/or the CO group.…”

“…17 (5)); 0.31 (s, Me 3 Si). 13 C-NMR (CDCl 3 ): 206.18 (C(1)); 199.87 (C(3')); 182.30 (C(3)); 136.81 (arom. C); 132.94 (1 arom.…”

“…IR (KBr): 2200 ± 3200m (br) , 1686vs, 1568vs, 1375vs, 1364vs, 1163s, 1138vs, 1070vs, 734s, 699s, 3.29 ± 3.33 (m, 2 HÀC(2')); 2.64 ± 2.68 (m, 2 HÀC(1')); 2.46 (t, J 6.3, 2 HÀC(4)); 2.31 (t, J 6.5, 2 HÀC(6)); 1.87 ± 1.95 (m, 2 HÀC (5)). 13 1685vs, 1638m, 1596s, 1562vs, 1378vs, 1311vs, 1281vs, 1248vs, 1175s, 1147vs, 1064vs, 1050vs, (6)); 1.03 (s, 2 Me). 13 (4)).…”

“…13 1685vs, 1638m, 1596s, 1562vs, 1378vs, 1311vs, 1281vs, 1248vs, 1175s, 1147vs, 1064vs, 1050vs, (6)); 1.03 (s, 2 Me). 13 (4)). 13 2-(3-Oxo-3-phenylpropyl)cyclohexan-1-one (7) [25].…”

“…13 (4)). 13 2-(3-Oxo-3-phenylpropyl)cyclohexan-1-one (7) [25]. A mixture of cyclohexanone (4 mmol) and 3-(dimethylamino)-1-phenylpropan-1-one hydrochloride (2 mmol), and Et 3 N (3 mmol) was heated at 1608 for 20 min.…”