¹³C Nuclear Magnetic Resonance of Some Acetanilides

Abstract

13C NMR spectra were measured for eleven mono-substituted aceranilides in 10 mol dimethylsulfoxide solution and the electron densitiea for these compounds were calculate by means of CNDO/2 MO method. The 13C chemical shifts for sp2 carbons in m- and p-substitude compounds are in parallel with the electron densities at the positions (Figs. 4 and s) On the other hand, for the o-substituted compounds, the correlation is not so good and it is considered to be due to the effect of steric compression or intramolecular hydrogen bonding between the amide and the substituents.
Changes in chemical shifts for the carbonyl carbons due to the alternation of substituent in benzene ring are extremely small (belew 1, 5ppm) and this result is in good agreement with in the total electron den.sities obtained by CNDO/2 calculation.
In p-substituted acetanilides, the linear relationship between the chemical shifts of 13C at the para position with respect to substituted group and the total electron denslties are observed (Fig.6). While the chemical shifts and the -electron densities as not correlate to each other.
13C chemical shifts at the carbon to which the substituent attaches in m-and p-substituted acetanilides, are correlated well with Pauling's electronegativity of the atom bonded directly to the ring carbon, and it is in agreement with the behavior in mono-substituted benzenes (Fig.8).