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, generated by radiolytic oxidation of the parent compound in argon and Freon matrices at low temperatures, undergoes a spontaneous rearrangement to form the distonic 1,1-dimethyleneallene (or 2-vinylideneallyl) radical cation 3•+ consisting of an allyl radical substituted at the 2-position by a vinyl cation. In similar matrix studies, it is found that the isomeric dimethylenecyclopropane radical cation 2•+ also rearranges to 3 •+ . The unusual molecular and electronic structure of 3•+ has been established by the results of ESR, UV-vis, and IR spectroscopic measurements in conjunction with detailed theoretical calculations. Also of particular interest is an NIR photoinduced reaction by which 3 •+ is cleanly converted to the vinylidenecyclopropane radical cation 4•+ , a process that can be represented in terms of a single electron transfer from the allyl radical to the vinyl cation followed by allyl cation cyclization. The specificity of this photochemical reaction provides additional strong chemical evidence for the structure of 3•+ . Theoretical calculations reveal the decisive role of vibronic coupling in shaping the potential energy surfaces on which the observed ring-opening reactions take place. Thus vibronic interaction in 1•+ mixes the 2 A 1 ′ ground state, characterized by its "non-bonding" 3a 1 ′ SOMO, with the 2 E′′ first excited state resulting in the destabilization of a lateral C-C bond and the initial formation of the methylenebicyclobutyl radical cation 5•+ . The further rearrangement of 5 •+ to 3 •+ occurs via 2 •+ and proceeds through two additional lateral C-C bond cleavages characterized by transition states of extremely low energy, thereby explaining the absence of identifiable intermediates along the reaction pathway. In these consecutive ring-opening rearrangements, the "non-bonding" bridgehead C-C bond in 1•+ is conserved and ultimately transformed into a normal bond characterized by a shorter C-C bond length. This work provides strong support for the Heilbronner-Wiberg interpretation of the vibrational structure in the photoelectron spectrum of 1 in terms of vibronic coupling.

Forty-one plant essential oils were tested under field conditions for the ability to reduce the attraction of adult Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae), to attractant-baited or nonbaited traps. Treatments applied to a yellow and green Japanese beetle trap included a nonbaited trap, essential oil alone, a Japanese beetle commercial attractant (phenethyl proprionate:eugenol:geraniol, 3:7:3 by volume) (PEG), and an essential oil plus PEG attractant. Eight of the 41 oils reduced attractiveness of the PEG attractant to the Japanese beetle. When tested singly, wintergreen and peppermint oils were the two most effective essential oils at reducing attractiveness of the PEG attractant by 4.2x and 3.5x, respectively. Anise, bergamont mint, cedarleaf, dalmation sage, tarragon, and wormwood oils also reduced attraction of the Japanese beetle to the PEG attractant. The combination of wintergreen oil with ginger, peppermint, or ginger and citronella oils reduced attractiveness of the PEG attractant by 4.7x to 3.1x. Seventeen of the 41 essential oils also reduced attraction to the nonbaited yellow and green traps, resulting in 2.0x to 11.0x reductions in trap counts relative to nonbaited traps. Camphor, coffee, geranium, grapefruit, elemi, and citronella oils increased attractiveness of nonbaited traps by 2.1x to 7.9x when tested singly, but none were more attractive than the PEG attractant. Results from this study identified several plant essential oils that act as semiochemical disruptants against the Japanese beetle.

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