ACIDITY OF DIBASIC ACIDS .1. THE 2ND ACIDITY CONSTANT OF 9,10-DIHYDRO-ANTHRACENE AND ITS 9,10-SUBSTITUTED DERIVATIVES - EFFECT OF SUBSTITUENT AND COUNTER ION

The second equilibrium ion pair acidity constants (pK2) of 9,10-dihydr oanthracene, 9-phenyl-9,10-dihyroanthracene, 9,10-diphenyl-9,10-dihydr oanthracene and 9-cyano-9,10-dihydroanthracene with sodium, potassium and rubidium have been determined in tetrahydrofuran (THF) at 25-degre es-C in the concentration range 10(-5)-10(-2) mol dm-3. Equilibria wer e monitored by UV-VIS and H-1 NMR spectroscopies and the spectra of th e dimetallic and monometallic salts reported. The dimetallic salts of all the dibasic carbon acids studied behave as contact ion pairs in TH F. The pK2 of 9,10-dihydroanthracene is insensitive to substituent eff ect but is strongly dependent on the cation.