Acidity of dibasic carbon acids. Part 5.1–4 The second acidity constant of 9,10-dihydrodibenz[a,h]anthracene in tetrahydrofuran—geometry, charge distribution of dianion, structure of dimetallic salts

Abstract

The second equilibrium ion pair acidity constant (pK2) of 9,10-dihydrodibenz[a,h]anthracene (DBDHA, 1H2) with counter ions sodium (pK2 28.5) and potassium (pK2 30.4) has been determined in tetrahydrofuran (THF) at 298 K. This value is considerably lower than for other 9,10-dihydroanthracene derivatives. Disodium, dipotassium and dirubidium salts of DBDHA, i.e. 12-, exist as contact ion triplets in THF at 298 K, although the dilithium salt behaves as a solvent-separated ion triplet under the same conditions. In the dianion of DBDHA (12-) the negative charge is displaced from the deprotonated carbon atoms towards the outer benzene rings.