SYMMETRIES OF HYDROGEN-BONDED ENOL FORMS OF DIKETONES AS DETERMINED BY X-RAY PHOTOELECTRON-SPECTROSCOPY

The O1S ionization regions of malonaldehyde (1a), hexafluoroacetylacetone (1c), tropoione (3a), 9-hydroxyphenalenone (4), and 6-hydroxy-2-formylfulvene (5) all show two dominant ionizations arising from oxygens made inequivalent by virtue of an asymmetric H bond. 1H NMR studies of the transoid enol form of malonaldehyde in deuterated ethanol show that the apparent symmetry of the molecule on the NMR time scale cannot be explained by keto-enol equilibria since this latter process is far too slow. Additional NMR studies of the intramolecularly H bonded cisoid form of malonaldehyde in CFCI3- CD2CI2 solvents indicate that the upper limit for the effective barrier to interconversion of the Cs forms via the C2v form is no greater than 6 kcal/mol. Similar results were obtained with deuterated malonaldehyde. © 1979, American Chemical Society. All rights reserved.