Application of carbon-13 nuclear magnetic resonance spectroscopy to the analysis of charge distribution patterns in unsaturated carbonyl-containing compounds

Oxygen‐17 and Carbon‐13 Nuclear Magnetic Resonance. Chemical shifts of unsaturated carbonyl compounds and acyl derivatives

“…The assumption that these electrons are transferred to the oxygen atom allows the extrapolation that the gain of one 2p electron on this atom will generate a 1 7 0 shielding of -530+ 70 pprn. The gain of one 2p electron on a carbon atom generates a I3C shielding of approximatively -240 pprn [6]. The ratio 530/240 = 2.2 is comparable to the value calculated using the theory of Pople & Karplus applied to the comparison between 6 1 7 0 of aliphatic ethers and 6 I3C of the corresponding carbon atom in analogous alkanes [4].…”

“…The 6 I7O and 6 13C together with 1 7 0 linewidths measured for 14 a,,&-unsaturated aldehydes and ketones are collected in Table 1. For the alicyclic compounds, the n electron deficiencies at the carbon,& to the carbonyl group, Z;, were calculated following the treatment of Levin et al [6] (Table 1). It is apparent that within the series of the four methyl ketones, the I7O nucleus is found to be shielded when the Z i electron deficiency increases; the same is true for the comparison between the two aldehydes.…”

“…However, information can be obtained from 13C-NMR. data since the electrons gained by the oxygen atom have been lost by the Cg carbon atom [6].…”

Carbon‐13 n.m.r. spectra of 2,3‐dimethylenebicyclo[2.2.1]heptanes and 2,3‐dimethylene‐7‐oxabicyclo[2.2.1]heptanes

“…These observations can be attributed to homoconjugative and hyperconjugative interactions between the 5-keto and the C-3,3' methylene groups. 23 Interaction between the C-2,2' methylene and 5-keto groups is also apparent: a difference of 3.2-(-3,3)= 6.5 pprn between the E" and 8-effects of the carbonyl substituent on C-2' and C-2, respectively, is found. This value is larger than the difference of the carbonyl substituent effects on the SC of the olefinic carbons in 6,6-dimethyl-5-methylene-2-norbornanone (28)l' (See Table 5).…”