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

The negative ion chemistry and photoelectron spectra of [CH2=C(CH3)-C(CH2)(2)](-) and [(CH2)(2)C-C(CH2)(2)](-) have been studied. The negative ion photoelectron spectra reveal the tetramethyleneethane diradical, TME, to have two low-lying electronic states, (X) over tilde and (a) over tilde. The ground (X) over tilde state is assigned as [TME] (1)A and the excited (a) over tilde state as [TME] B-3(1). The energy separation between these states is about 2 kcal mol(-1); Delta E[(a) over tilde B-3(1) <-- (X) over tilde(1)A] congruent to 0.1 eV. The experimental electron affinities of the neutrals are: E-ea[CH2=C(CH3)-C(CH2)(2)] = 0.654 +/- 0.010 eV and E-ea[(CH2)(2)C-C(CH2)(2)] = 0.855 +/- 0.010 eV. The experimental gas phase acidities are: Delta(acid)H(298)[CH2=C(CH3)-C(CH2)CH2-H] = 388 +/- 3 kcal mol(-1) and Delta(f)H(298)[(CH2)(2)C-C(CH2)-CH2-H] = 388 +/- 4 kcal mol(-1). These findings can be used to establish the bond energies and heats of formation: DH298[CH2=C(CH3)-C(CH2)CH2-H] = 90 +/- 3 kcal mol(-1) and Delta(f)H(298)[(CH2)(2)C-C(CH2)=CH2] = 48 +/- 3 kcal mol(-1); DH298[(CH2)(2)C-C(CH2)CH2-H] = 94 +/- 4 kcal mol(-1) and Delta(f)H(298)[(CH2)(2)C-C(CH2)(2)] = 90 +/- 5 kcal mol(-1).