MASS SPECTROMETRY IN STRUCTURAL AND STEREOCHEMICAL PROBLEMS .168. EFFECT OF FLUORINE SUBSTITUTION ON MCLAFFERTY REARRANGEMENT OF ALIPHATIC KETONES

The mass spectra of allphatic ketones are drastically altered following substitution of a trifluoromethyl entity adjacent to the carbonyl group (II and III) or attachment to the γ‐carbon atom (V). Loss of the trifluoromethyl group by α‐cleavage far exceeds the alternative elimination of an alkyl radical. Virtually complete repression of the McLafferty rearrangement process (I → a) occurs when a CF3 group is attached to the γ‐carbon atom. A fluorine atom is not transferred in lieu of hydrogen in the McLafferty rearrangement as demonstrated by the mass spectrum of 1,1,1,7,7,7‐hexafluoroheptan‐4‐one (IV). Rationalization for these results are presented as is a description of the syntheses of several hitherto unknown fluorinated ketones. Copyright © 1969 John Wiley & Sons, Ltd.