1H nmr chemical shifts of [14]annulenes and their dianion salts

Abstract The bridged (14]annulene 2 was reduced into its dianion and the structure of the dianion salt was proven by chemical and spectroscopic means. The 1H NMR spectroscopic properties of 2 are similar to those of the structurally related bridged [14]annulene 1 , whereas the corresponding dianions 2 2- and 1 2- are strikingly different. The geometries of 1 and 2 and their dianions were studied by means of a modified π-SCF force field approach. Almost planar perimeters without significant bond length alternation are obtained for the neutral annulenes 1 and 2 , whereas their dianions are characterized by structures with reduced symmetry. The 1H chemical shifts of the bridged [14]annulenes a…