35Cl NQR spectra of substituted N-(phenyl)-2,2,2-trichloroacetamides

Several substituted acetamides, XyC6H5-y NHCOCCl3 (X=CH3, NO2, or Br and y = 1 or 2) have been synthesized and studied by NQR. The effect of ring substitution on the average nu (Cl-35) NQR of the trichloroacetyl group is not substantial, but it affects the crystal structure of the substituted compounds. The NQR spectra of XyC6H5-y NHCOCCl3 (where X-y=4-CH3, 4-NO2, and 2,3-(CH3)(2)) show six Cl-35 NQR frequencies, each indicating the presence of two molecules in their respective asymmetric units. The temperature dependence of nu (Cl-35) NQR of N-(4-methylphenyl)-2,2, 2-trichloroacetamide reveals that it undergoes a first order phase transition around 205 K. Its spectrum shows six lines up to 205 K and three lines thereafter. The latter triplet part of the spectrum fades out around 250 K due to librational motions in the crystal lattice, as the torsional motions of the CCl3, group are easily excited. The Cl-35 NQR spectra of all the methylsubstituted amides have been compared with those of the corresponding chlorosubstituted compounds. Generally there is no systematic variation of the mean values of nu(Cl-35) NQR or the trichloroacelyl group with the substituents in the phenyl ring. The omega C-Cl frequencies of the trichloroacetyl group of all the v-substituted N-(phenyl)-2,2,2-trichloroacetamides have been estimated using NQR substituent parameters (k) and the frequencies of N-(phenyl)-2,2,2-trichloroacetamide. Agreement between these values and the experimental frequencies is quite good. The nu(Cl-35) NQR of these amides has also been correlated with Sigma k(i) of the substituents. Further nu (Cl-35) NQR spectra of mono- and trichloroacetamides have been correlated.