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

Abstract

Formation of deuteriochloroform complexes with four series of N¹,N¹-dimethylamidines (R^xNCR¹NMe₂; 75 compounds) containing a variable substituent R^x at the imino nitrogen atom has been studied by infrared spectroscopy. 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 N²-alkyl and N²-aryl derivatives separate correlations are obtained. The slope of the correlation line depends on substituent R¹ at the amidino carbon atom, and for N²-aryl derivatives it increases with the increase of the volume of a substituent at the amidino carbon atom, whereas for N²-alkyl derivatives it decreases. The inverse order of the change of the slopes is attributed to the E–Z isomerism in amidines.