Ep. Clifford et al., Photoelectron spectroscopy, gas phase acidity, and thermochemistry of tert-butyl hydroperoxide: Mechanisms for the rearrangement of peroxyl radicals, J CHEM PHYS, 109(23), 1998, pp. 10293-10310
The 3.531 eV negative ion photoelectron spectra of the hydroperoxide ion an
d the tert-butylperoxide ion have been studied. We find HO2-+(h) over bar o
mega(351.1 nm)-->HO2+e(-) EA[HO2,(X) over tilde (2)A "]=1.089+/-0.006 eV, (
CH3)(3)COO-+(h) over bar omega(351.1 nm)-->(CH3)(3)COO+e(-) EA[(CH3)(3)COO,
(X) over tilde (2)A "]=1.196+/-0.011 eV. The photoelectron spectra show det
achment to the ground state of the peroxyl radicals and to a low lying elec
tronic state. The intercombination gaps are measured to be Delta E((X) over
tilde (2)A "-(A) over tilde (2)A')[HO2]=0.871+/-0.007 eV and Delta E((X) o
ver tilde (2)A "-(2)A')[(CH3)(3)COO]=0.967+/-0.011 eV. The gas phase acidit
y of (CH3)(3)COOH was measured in a tandem flowing afterglow-selected ion f
low tube (FA-SIFT) to be Delta(acid)G(298)=363.2+/-2.0 kcal mol(-1) and we
find Delta(acid)H(298)[(CH3)(3)COO-H]=370.9+/-2.0 kcal mol(-1). Use of Delt
a(acid)H(298)[(CH3)(3)COO-H] and EA[(CH3)(3)COO] leads to the bond energies
DH298[(CH3)(3)COO-H]=85+/-2 kcal mol(-1) and D-0[(CH3)(3)COO-H]=83+/-2 kca
l mol(-1). The thermochemistry of the alkylperoxyl radicals, RO2, is review
ed. A mechanism for the rearrangement of chemically activated peroxyl radic
als is proposed [RO2](X) over tilde (2)A "-->[RO2]*(A) over tilde (2)A'-->a
ldehydes/ketones+HO((2)Pi), [RO2](X) over tilde 2A "-->[RO2]*(A) over tilde
2A' -->alkenes+HO2((X) over tilde (2)A "). (C) 1998 American Institute of
Physics. [S0021-9606(98)01925-4].