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. 1^2-, 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 (1^2-) the negative charge is displaced from the deprotonated carbon atoms towards the outer benzene rings.