Carbonyl group carbon-13 chemical shifts

The carbon spectrum of this compound (Fig. 5.8) is typical of such spectra, with the CF3 group and the carbonyl group having chemical shifts of 8 115.7 and 192.1, respectively, and F—C couplings of 292 and 34 Hz, respectively. In this case, no three-bond F—C coupling is able to be discerned at the CH2 carbon, which appears as a broad singlet at 30.1 ppm. 

H and 13C NMR Data. A ketone or aldehyde carbonyl group bound to a CF2H group shields its proton slightly (0.1 ppm), and even more surprisingly it also has a shielding effect upon its carbon chemical shift of about 8 ppm (Scheme 4.42). By comparison, a hydrocarbon... 

A fourth HMBC correlation is detected between the methylene protons N and the most deshielded carbon. That carbon (Ci) appears to be an ester carbonyl from its chemical shift (8 173.0, Section 3-5c) and exhibits a second connectivity to H. This correlation is crucial because it is the only one that connects Ci indirectly to C9 (via an oxygen as an isovaleryl ester group) of the presumptive cyclohexene fragment. If the connection is confirmed, the molecular fragment 8-1 (with HMBC connectivities shown) accounts for three units of unsaturation and 12 carbons (including the previously surmised carbon-carbon double bond), 17 hydrogens, and 2 oxygens. 

Carbon-13 NMR spectra of tungsten derivatives (CO)sWC(CH3)(SC6H4Y) were obtained by Ward et al. (127) (Table XXXVII). Only small variations of cis and trans carbonyl and carbene carbon chemical shift were detected as the nature of the para group, Y, was varied. The authors concluded that the lack of any conjugative effect indicated that the phenyl ring was probably perpendicular to the carbene plane. 

The induced field of a carbonyl group (C=0) deshields protons in much Ihe same way lhal a carbon-carbon double bond does and Ihe presence of oxygen makes il even more eleclron wilhdrawmg Thus protons attached to C=0 m aldehydes are Ihe leasl shielded of any protons bonded to carbon They have chemical shifts m Ihe range 8 9-10... 

Table 7.55 Carbon-13 Chemical Shifts of Carbonyl Group 7.106...

Study of the mechanism of this complex reduction-Hquefaction suggests that part of the mechanism involves formate production from carbonate, dehydration of the vicinal hydroxyl groups in the ceUulosic feed to carbonyl compounds via enols, reduction of the carbonyl group to an alcohol by formate and water, and regeneration of formate (46). In view of the complex nature of the reactants and products, it is likely that a complete understanding of all of the chemical reactions that occur will not be developed. However, the Hquefaction mechanism probably involves catalytic hydrogenation because carbon monoxide would be expected to form at least some hydrogen by the water-gas shift reaction. 

It is evident from Table 2 that the chemical shift data are very similar in both states of aggregation. Only the carbonyl carbon show a small but definite shifts, 2 ppm. In the solution state, in acetone -d6 solution the relaxation times T1 of the pyranose carbon atoms are very similar and only slightly smaller than those of the carbon atom of the methyl group in the acetyl substituent, while the T1-value of the carbon atom of the carbonyl group is considerably higher. 

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