Properties of tetramethyleneethane (TME) as revealed by ion chemistry and ion photoelectron spectroscopy
The negative ion chemistry and photoelectron spectra of [CH2C(CH3)–C(CH2)2]– and [(CH2)2C–C(CH2)2]– have been studied. The negative ion photoelectron spectra reveal the tetramethyleneethane diradical, TME, to have two low-lying electronic states, and ã. The ground state is assigned as [TME] 1A and the excited ã state as [TME] 3B1. The energy separation between these states is about 2 kcal mol–1; ΔE[ã 3B1 ← 1A] ≊ 0.1 eV. The experimental electron affinities of the neutrals are: Eea[CH2C(CH3)– C(CH2)2] = 0.654 ± 0.010 eV and Eea[(CH2)2C–C(CH2)2] = 0.855 ± 0.010 eV. The experimental gas phase acidities are: ΔacidH298[CH2C(CH3)–C(CH2)CH2–H] = 388 ± 3 kcal mol–1 and ΔacidH298[(CH2)2C–C(CH2)CH2–H] = 388 ± 4 kcal mol–1. These findings can be used to establish the bond energies and heats of formation: DH298[CH2C(CH3)–C(CH2)CH2–H] = 90 ± 3 kcal mol–1 and ΔfH298[(CH2)2C–C(CH3)CH2] = 48 ± 3 kcal mol–1; DH298[(CH2)2C–C(CH2)CH2–H] = 94 ± 4 kcal mol–1 and ΔfH298[(CH2)2C–C(CH2)2] = 90 ± 5 kcal mol–1.