Cl NQR Spectra of N-(substitutedphenyl)-2,2-dichloroacetamides and Correlation of ³⁵ Cl NQR γCl(ω) of Substituted N-Phenyl- Chloroacetamides X_yC₆H_5-yNHCOR (X = Cl or CH₃ , y = 1 or 2, R = CH₂Cl, CHCl₂ or CCl₃)

Abstract

To study the effect of electron donating or repelling group substitution in the phenyl ring on the γ(³⁵ Cl NQR of Cl(ω)) of the dichloroacetyl group, several N-(methylsubstituted-phenyl)-2,2-dichloroacetamides have been synthesised, characterised and their ³⁵ Cl NQR frequencies mea-sured at 77 K. All the substituted amides, except N-(2,5-dimethylphenyl)-2,2-dichloro-acetamide, show two ω-C-Cl frequencies in the range of 37.009 -38.014 MHz. N-(2,5-dimethylphenyl)-2,2-dichloroacetamide shows one u-C-C 1 NQR frequency at 37.50 MHz for the two chlorine atoms present. The two atoms may be crystallographically equivalent. The frequencies of all the methyl-substituted dichloroacetamides have been compared and correlated alongwith the corresponding chloro substituted-phenyl dichloroacetamides. The γ(³⁵ C1 NQR) of Cl(ω) of all the N-(substituted-phenyl)-2,2-dichloroacetamides have been correlated with the NQR substituent parameters (κ_i), assuming additivity of the substituent effects. The frequencies are also correlated with Hammett a. The effect of ring substitution on the average ³⁵ Cl NQR Cl(ω) frequencies of the dichloroacetyl group is not substantial, but it affects the crystal structures of the substituted compounds. Using the K_i values for various groups and ω-C-Cl NQR frequencies of N-(phenyl)-2,2-dichloroacetamide (37.195 and 37.596 MHz), 7(35 C1 NQR) of all the N-(methyl and chlorosubstitutedphenyl)-2,2-dichloroacetamides have been estimated. Similar calculations are extended to all the N-(methyl and chlorosubstitutedphenyl)-2-chloroacetamides and -2,2,2-trichloroacetamides. There is a rea-sonably good agreement between the computed and the experimental values for all the three groups of compounds. Further, γ(³⁵ Cl NQR of Cl(ω) of all the substituted N-phenyl-chloroacetamides represented by the general formula X_yC₆H_{5- y} NHCOR (where X = Cl, or CH₃ , y = 1 or 2 and R = CH ₂ Cl, CHCl₂ or CCl₃) are compared. The γ(³⁵Cl NQR of Cl(ω)) of the substituted N-(phenyl)-2,2-dichloroacetamides lie between the frequencies of the corresponding substituted N-(phenyl)-2-chloroacetamides and substituted N-(phenyl)-2,2,2-trichloroacetamides.