Potential energy surface for unimolecular dissociations and rearrangements of the ground state of [C2H3FO] systems

Abstract

The potential energy surface (PES) of [C₂H₃FO] systems in its electronic ground state has been investigated using density functional theory method, at the B3LYP/6-311++G(d,p) level. Ten stable intermediates, including acetyl fluoride (1), fluoroacetaldehyde (9), 1-fluorovinyl alcohol (4), 2-fluorovinyl alcohol, carbenes and fluorooxiranes, have been located. Most stationary points on the PES corresponding to the molecular elimination and rearrangement channels from these intermediates have been identified. Ketene (8) is found to be the predominant product in the unimolecular dissociations of 1, 4, 9 and fluorooxirane (6). The most probable channels for ketene formation from acetyl fluoride are 1→8 and 1→4→8. In the reactions of both CH₃CO and F radicals, both these processes are energetically feasible for the thermal reactants and hence should lead to a spontaneous emission of vibrationally hot HF. The present PES characterises the CH₃CO+F reaction to be a capture-limited association–elimination reaction with a very high and pressure-independent rate coefficient. In addition to its direct decomposition to ketene, 9 can give rise to stable rearrangement products, viz., 2-fluorovinyl alcohol (12) and 6. Fluorooxirane (6) decomposes to ketene through its isomerisation to 9 as intermediate and the present study provides an explanation for the non-observation of this intermediate.