The radiation chemistry of dihydromyrcene

Dihydromyrcene was irradiated with 1-MeV electrons at room temperature both in the pure state and in benzene solution. The main reactions observed, and their G-values for the pure diisoprene, were loss of unsaturation (~7.8–9.9), cross-linking (or dimerization) (2.4–2.6), evolution of hydrogen (0.81), and trans → cis isomerization (< 0.5). As with squalene, the loss of double bonds in dihydromyrcene occurred only in the cross-linked residue, obtained on distillation of the irradiated isoprenoid. Although the residue (mainly dimer, with some trimer) was considered to be partially cyclized, no cyclization of uncross-linked (monomeric) dihydromyrcene was observed. Dihydromyrcene in 10% benzene solution (by weight) showed trans → cis and cis → trans isomerization with G-values of 0.63 and 1.2, respectively, hydrogen evolution with a G-value of 0.08, and a higher rate of loss of original unsaturation than in the pure state.