PNNL

Abstract

A great deal of efforts has been focused on developing metal-free catalytic system for epoxidation of unreactive alkenes. Fluoroketones are thought as remarkably promising catalysts for epoxidation reactions. The combination of fluorinated alcohols and catalytic amounts of hexafluoroacetone (HFA) gives a versatile and effective medium for epoxidation of various olefins with hydrogen peroxide. However, the fundamental physicochemical properties of HFA remained largely unclear, although they were very important to understand the related interactions. Here, we performed a joint study on electron affinity and electronic structure of HFA employing negative ion photoelectron (NIPE) spectroscopy and quantum chemistry calculations. Two distinct bands with complicated vibrational progressions were observed in the NIPE spectrum with the adiabatic / vertical detachment energies being 1.48 / 2.11, and 4.41 / 4.86 eV, respectively. Using the optimized geometries and vibrational frequencies of the anion and the neutral, the Franck-Condon factors were calculated for electron detachments to produce HFA in its lowest singlet and triplet states. An excellent agreement was obtained hereby for both bands between the experimental and calculated NIPE spectra, when taking into account combination vibrational excitations, unequivocally revealing that HFA possesses a singlet ground state with a giant singlet-triplet energy difference (?EST). The electron affinity (EA) and (?EST) of HFA was therefore determined to be EA = 1.48 ± 0.01 eV and ?EST = - 3.01 eV.