In higher plants the C11 homoterpene 4,8-dimethylnona-1,3,7-triene (1) originates from oxidative degradation of nerolidol (3) or geranylacetone (4). The geometry of the transition state of bond cleavage has been shown to be syn-periplanar, for both 3 and 4 by application of chirally labelled, deuterated precursors to flowers of Magnolia liliiflora nigra or leaves of the Lima bean Phaseolus lunatus