In 2,6‐di‐unsaturated carbonyl compounds, two successive, site‐specific hydrogen transfers are necessary to account for the loss of carbon atoms 1, 2, 3 and 4, together with one hydrogen from C‐8. The deuterated methyl geranate required for this study was readily converted to pseudo‐ionone, in which a similar fission was shown to occur. Previous predictions about the β‐ionone mass spectrum2 have been shown to be substantially correct, and its similarity to the mass spectra of benzylidence acetones is pointed out. Copyright © 1969 John Wiley & Sons, Ltd.