J. Phys. Chem. 98 (1994) 3650-3657
Distinguishing Keto and Enol Structures by Inner-shell Spectroscopy

J.T. Francis and A.P. Hitchcock

Department of Chemistry McMaster University, Hamilton, Ontario L8S 4Ml, Canada
Oscillator strengths for C 1s and O 1s excitation of gas phase 1,2-cyclohexanedione, 1,3-cyclohexanedione, 1,4-cyclohexanedione and cyclohexanone have been derived from electron energy loss spectra recorded under conditions of electric dipole scattering. Spectral assignments have been aided by extended Hückel (EHMO) and HAM/3 calculations. Spectral features characteristic of diketo and mono-enol structures are identified. The C 1s and O 1s spectra clearly indicate that 1,2-cyclohexanedione has a mono-enol structure in the gas phase while 1,3-cyclohexanedione is predominantly in the diketonic structure in the gas phase. The latter result resolves an existing literature discrepancy concerning the preferred gas phase tautomer of 1,3-cyclohexanedione.  
©1994  American Chemical Society