Fourier transform microwave spectroscopy of Criegee intermediates: The conformational behaviour of butyraldehyde oxide.

Four conformers of the n-propyl-substituted Criegee intermediate, CHCHCHCHOO, also named n-butyraldehyde oxide, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodobutane/O diluted in Ar or Ne. The observation of only syn species is in contrast to the results of other previous studies of alkyl-substituted Criegee intermediates, in particular, those for the structural isomers, isobutyraldehyde oxide ((CH)CHCHOO), and methyl-ethyl-ketone oxide (CHC(CH)OO), for which syn and anti species have been observed coexisting in the gas phase.