Properties of tetramethyleneethane (TME) as revealed by ion chemistry and ion photoelectron spectroscopy

Abstract

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: E_ea[CH₂C(CH₃)– C(CH₂)₂] = 0.654 ± 0.010 eV and E_ea[(CH₂)₂C–C(CH₂)₂] = 0.855 ± 0.010 eV. The experimental gas phase acidities are: Δ_acidH₂₉₈[CH₂C(CH₃)–C(CH₂)CH₂–H] = 388 ± 3 kcal mol^–1 and Δ_acidH₂₉₈[(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 Δ_fH₂₉₈[(CH₂)₂C–C(CH₃)CH₂] = 48 ± 3 kcal mol^–1; DH₂₉₈[(CH₂)₂C–C(CH₂)CH₂–H] = 94 ± 4 kcal mol^–1 and Δ_fH₂₉₈[(CH₂)₂C–C(CH₂)₂] = 90 ± 5 kcal mol^–1.