Energies of C2H5O and C2H5O+ isomers

Abstract

The Gaussian-2 (G2) theoretical procedure, based on ab initio molecular orbital theory, is used to calculate the energies of C2H5O and C2H5O+ isomers. The ethoxy radical cation (CH3CH2O+) is found to have a 3A″ ground state while the singlet state is predicted to be unstable to rearrangement. The G2 adiabatic ionization potential of ethoxy radical is 10.32 eV in good agreement with a new ionization potential reported by Ruscic and Berkowitz of 10.29±0.08 eV from photoionization studies. The 2-hydroxyethyl radical (CH2CH2OH) has three isomers of nearly equal energy (within 1.6 kcal/mol). No stable 2-hydroxyethyl cation was located as it collapses to either O-protonated oxirane or 1-hydroxyethyl cation. The G2 appearance potential of CH3CHOH+ from ethanol of 10.79 eV is in excellent agreement with the recent photoionization value of 10.801±0.005 eV. The α(C–H), β(C–H), and O–H bond dissociation energies of ethanol are 94.9, 101.9, and 104.6 kcal/mol, respectively. The G2 result for the O–H bond energy is in good agreement with experiment while the results for the other two bond energies suggest that the experimental values for these quantities may be low.