Amidines. Part 40. Amidine-deuteriochloroform complexes. Influence of amidine basicity on the frequency of C-D stretching vibrations

Formation of deuteriochloroform complexes with four series of N-1,N-1-dimet hylamidines ((RN)-N-x=(CRNMe2)-N-1; 75 compounds) containing a variable sub stituent R-x at the imino nitrogen atom has been studied by infrared spectr oscopy. It is found that for complexed CDCl3 molecules a new, additional C- D stretching band appears at lower frequencies. The changes in frequency of this band depend on the basicity of the amidine and correlate with the pK( a) values of complexing amidines, however for N-2-alkyl and N-2-aryl deriva tives separate correlations are obtained. The slope of the correlation line depends on substituent R-1 at the amidino carbon atom, and for N-2-aryl de rivatives it increases with the increase of the volume of a substituent at the amidino carbon atom, whereas for N-2-alkyl derivatives it decreases. Th e inverse order of the change of the slopes is attributed to the E-Z isomer ism in amidines.