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 υ(35Cl) NQR of the trichloroacetyl group is not substantial, but it affects the crystal structure of the substituted com-pounds. The NQR spectra of XyC6H5-y NHCOCCl 3 (where Xy =4-CH3 , 4-NO2 , and 2,3-(CH3)2) show six 35Cl NQR frequencies, each indicating the presence of two molecules in their respective asym-metric units. The temperature dependence of υ(35Cl) NQR of N-(4-methylphenyl)-2,2,2-trichloroacet-amide 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 excit-ed. The 35Cl 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 val-ues of υ(35Cl) NQR or the trichloroacetyl group with the substituents in the phenyl ring. The ω 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-tri-chloroacetamide. Agreement between these values and the experimental frequencies is quite good. The υ(35Cl) NQR of these amides has also been correlated with Σki of the substituents. Further υ(35Cl) NQR spectra of mono-and trichloroacetamides have been correlated.