E.s.r. studies of ion association. Part 5.—New observations on the complex of m-dinitrobenzene and alkali metals

Abstract

Complexes of m-dinitrobenzene (MDNB) and 1,3-dinitro-5-t-butyl benzene (TBMDNB) with alkali metals in 1,2-dimethoxyethane have been studied by e.s.r. The behaviour of TBMDNB is analogous to that of MDNB itself, but the spectra are simpler. General observations agree with those of other workers. Several new observations have been made: (i) the rate constant for intramolecular caesium exchange in Cs—TBMDNB is 4 × 10¹⁰ exp(–14,300 (J)/RT). (ii) The spin density at the t-butyl protons in Na—TBMDNB is negative. (iii) Na—TBMDNB exists in equilibrium with a different complex, whose e.s.r. spectrum shows no alkali metal hyperfine splitting, at high temperature. At 97°C, K= 0.25, ΔG°₃₇₀=+ 4.2 kJ M^–1, ΔH°=–24.8 kJ M^–1, ΔS°₃₇₀=+ 77.6 J deg.^–1 M^–1. (iv) The equilibrium Cs—MDNB + NaBPh₄= Na—MDNB + CsBPh₄ has K= 15 at 23°C. ΔH° and ΔS°₂₉₆ are positive.