¹³C N.M.R. Spectra of ortho-Substituted Phenyl N,N-Dimethyl-Carbamates and N-Methyl Carbamates

Abstract

We measured ¹³C nuclear magnetic resonance spectra of O-substituted phenyl N,N- dimethyland N-methyl- carbamates and compared the results with those for the corresponding m- and p-substituted derivatives. The additivity relationship on the basis of the substituent chemical shift for monosubstituted benzenes ( scs_phx ) did not hold well because of the ortho effect. However, the scs of C2(ipso), C3(ortho) and C5(para) was correlated excellently with scs_phxX . Dual substituent parameter (DSP) analyses of the scs of C5 and the carbonyl carbon in the fixed side chain showed that correlation was very good for C5 but moderate for C=O. These observations suggested that the X substituent lay in almost the same plane as the aromatic ring, whereas the OCONMe₂ group may have changed its conformation somewhat. In O-substituted derivatives, the carbon nucleus that is directly attached to the aromatic ring (γ to the oxygen; OCONMe₂)had a pronounced upfield shift relative to the corresponding m- and p-substituents by 4-5 ppm . This phenomenon was explained by the γ-effect caused by the oxygen atom.