10-methyl-9-phosphaanthracene

The synthesis of 10-methyl-9-phosphaanthracene ( 1b ) is described. Its stability is found to be intermediate between that of the unsubstituted parent compound ( 1a ) and of the 10-phenyl derivative ( 1c ). The electronic structure of this new phosphaaromatic system is studied, especially by photoelectron spectroscopy. As inductive and/or conjugative effects of the substituents are shown to be of minor importance, it is concluded that mainly steric effects stabilize the 9-phosphaanthracene system.