INTERNAL HYDROGEN REARRANGEMENT AS A FUNCTION OF ION LIFETIME IN MASS SPECTRA OF ALIPHATIC KETONES

From a study of various specifically deuterated aliphatic ketones, it has been shown that internal hydrogen rearrangement (H/D scrambling) occurs at a rate which is slow on the time scale of the mass spectrometer. Single-bond cleavage processes show little evidence of H/D scrambling at 70 eV because the rate of fragmentation is much faster than that of the scrambling processes. On the other hand, fragmentation processes accompanied by rearrangement show signs of H/D scrambling prior to the formation of the fragment ions at 70 eV because such processes occur with k vs. E curves that are comparable to those of the scrambling processes. Ions of relatively long lifetimes, such as those decomposing in the first and second field-free regions of the MS-9 double focussing mass spectrometer show extensive H/D scrambling prior to all the various decompositions. The relationship between lifetime and the extent of H/D scrambling requires that great care must be exercised in the interpretation of deuter um-labeling data, particularly when rearrangement processes are implicated. © 1969, American Chemical Society. All rights reserved.