Steric hindrance to termolecular complex formation in an electron-donor–acceptor complex of 2,7-dinitro-1,6-methano[10]annulene

Abstract

N.m.r. shift measurements of carbon tetrachloride solutions containing 2,7-dinitro-1,6-methano[10]annulene as an electron acceptor in the presence of large excesses of NNN′N′-tetramethyl-p-phenylenediamine as an electron donor indicate that complexes with only 1 : 1 stoicheiometry are formed, whereas if the electron acceptor is p-dinitrobenzene, 1 : 1 and 2 : 1 complexes are formed. This difference can be accounted for in that p-dinitrobenzene is able to accommodate one donor molecule above and another below the acceptor molecular plane, whereas the annulene ring has one side which effectively sterically hinders the approach of a donor molecule.