Reactions of radical anions. Part IV. The dimerisation of the tolan radical anion

Abstract

The tolan radical anion has been produced by mixing an alkali metal–aromatic hydrocarbon with tolan (diphenylacetylene) in slight excess in tetrahydrofuran as solvent. The reactions we have studied in this system are: PhCCPh + M⁺ArH^–→(PhCCPh)[graphic omitted]M⁺+ ArH (1)(I) Yellow-green 2(PhCCPh)[graphic omitted]M⁺→ PhCCPh–CPhCPh (2)M M (II) Green Reaction (1) was too fast for its rate to be measured. Reaction (2) was very fast, but its rate could be measured at low temperature by use of a stop-flow technique.

Reaction (1) was studied by use of different aromatic hydrocarbons so as to find the electron affinity of tolan under these conditions. It was found to lie between that of chrysene (2·70 eV). and pyrene (2·96 eV). Reaction (2) was studied with Li⁺, Na⁺, K⁺, and Cs⁺ as gegen-ions and the following values obtained for the thermodynamic constants: ΔG₂^‡: Li⁺ 15·3, Na⁺ 14·8, K⁺ 14·5, Cs⁺ 15·5 kcal. mole^–1; ΔH₂^‡: Li⁺ 14·5, Na⁺ 18·0, K⁺ 13·9, Cs⁺ 13·7 kcal. mole^–1; ΔS₂^‡: Li⁺–3·0, Na⁺ 12·0, K⁺–2·2, Cs⁺–6·6 cal. mole^–1 deg.^–1.