Carbon 13 chemical shifts ethyl compounds

Z Arrangement was also ascribed to the isomer absorbing at higher field in the case of the ethyl compounds. CH and CH2 protons near the ring nitrogen are shielded by the aromatic ring in the Z compound. The protons at the ring carbon absorb at lower field (near 5.2 p.p.m.) in the Z compounds than in the E compounds (4.50-4.70 p.p.m.). The chemical shift of this proton may be used for E-Z discrimination in further substances. 

V. Allenes. Allenes form a unique class of compounds because of the extremely low field shift of the central allenic carbon C2 (200 to 220 ppm). Table 5 presents representative data for a number of substituted allenes. For a given alkyl substituent, there is a linear relationship between the number of substituents and the chemical shift of the central carbon. The shielding is regarded as an additive property, a methyl group shields that carbon by 3.3 ppm, an ethyl group by 4.8 ppm and a. sec-alkyl group by 7 ppm. Carbons Cl and C3 are shielded by some 30 ppm relative to corresponding ethylene carbons but otherwise display similar substituent effects. Strain in cyclic allenes appears to have little effect. 

Hz) between C(l) and C(2) for this compound, and its comparison with that (79.2 Hz) for the alkenic carbons of ( )-l-diethylamino-l-butene (19) (see above), indicate that substitution of the vinyl group for the ethyl group at C(2) of an enamine slightly decreases this coupling. The NMR data (Table 6) for some derivatives of 98 show that the chemical shifts of the carbon atoms are disposed in the order 3C(1) < 5C(4) < C(3) < C(2) as anticipated. 

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