Simple theoretical considerations of counterion effects on proton chemical shifts in charged annulenes
Abstract
Ring-current contributions to 1H chemical shifts of charged annulenes with (4m+ 2) and (4m)π-electrons are investigated by means of simple molecular orbital theory. It is shown that electrostatic and covalent interaction between annulene and counterion reduce the paratropism of (4m)π-electron annulenes but do not affect the diatropism of (4m+ 2)π-electron annulenes.