DYNAMIC NMR-STUDY OF THE FLEXIBILITY OF 2-AMINO-3-AROYL-4,6-DIARYL-PYRYLIUM SALTS

Dynamic NMR investigations of a number of 2-amino-3-aroyl-4,6-diaryl-p yrylium salts were carried out. The barrier to rotation of the partial C, N double bond was determined and proved to be in the range of 62 t o 63 kJ/mol. Quantum chemical calculations of bond orders and electron densities of the different atoms in the molecules show the distinct d ouble bond character of the exocyclic C, N bond. This is in agreement with the relatively high barrier to rotation. By quantum chemical ab i nitio 3-21G calculations, the dynamic behaviour of this kind of compou nds was simulated; two pairs (image and mirror image) of ground state conformations, in coincidence with the experiment, were obtained.