Acidity of dibasic carbon acids. Part 3. Ion salvation state of monometallic salts of 9,10-dihydroanthracene and its derivatives in THF

Abstract

The ion solvation state of monometallic salts of 9,10-dihydroanthracene (DHA) and its 9,10-disubstituted derivatives in THF has studied by UV–VIS and ¹H and ¹³C NMR spectroscopy. At room temperature, lithium 9-phenyl-9,10-dihydroanthracen-9-ide, lithium 9,10-dimethyl-9, 10dihydroanthracenide and lithium 9,10-diphenyl-9,10-dihydroanthracemde exist as solvent separated ion pairs (SSIP). Lithium 9,10-dihydroanthracene, lithium 9-methyl-9,10-dihydroanthracen-10-ide and sodium, potassium and rubidium 9-phenyl-9,10-dihydroanthracen-9-ides, 9,10-dimethyl-9, 10dihydroanthracenides and 9,10-diphenyl-9,10-dihydroanthracenides exist as a mixture of SSIP and contact ion pairs (CIP). Sodium, potassium, rubidium and caesium 9,10-dihydroanthracenides, 9-methyl-9,10-dihydroanthracen-10-ides and 9-cyano-9,10-dihydroanthracenides exist as CIP in solution. The stabilizing effect of the methyl and phenyl substituents is more significant for SSIP than for CIP. The thermodynamics for SSIP to CIP conversion is determined for the sodium salts of DHA and its derivatives. ΔS° is 27 ± 2 cal mol^–1 K^–1ΔH° increases with substituent size and charge dispersion. A model for the transition of CIP of alkali-metal salts of DHA and its derivatives into SSIP is suggested. The model takes into account the geometry and charge distribution in anions.