THE DIMETHYLENE KETENE RADICAL-CATION

Molecular orbital calculations (at the Becke3LYP/6-31G(d) level of the ory) indicate that the distonic ion (CH2C)-C-.(CH2)CO+ is planar and h as C-2 upsilon symmetry. Most of the positive charge resides at the ca rbonyl carbon while the odd spin is delocalized over the allyl group. A similar spin distribution was calculated for the allyl radical. Henc e, the reactivity of (CH2C)-C-.(CH2)CO+ toward spin traps may be expec ted to resemble that of the neutral allyl radical. This issue was exam ined experimentally by using Fourier transform ion cyclotron resonance mass spectrometry. Similar to other carbon-centered free radicals, th e gaseous (CH2C)-C-.(CH2)CO+ abstracts H-. from benzeneselenol, CH3Se. from dimethyl diselenide, and I-. from allyl iodide. However, some of these reactions occur at efficiencies that suggest catalysis by the c harged group. Further, the reaction of (CH2C)-C-.(CH2)CO+ with dimethy l disulfide was found to proceed in an unprecedented manner. In additi on to the expected formation of CH3SCH2C(CH2)CO+ and CH3S. (via CH3S. abstraction), a new distonic ion, (CH3SCHC)-C-.(CH2)CO+, is generated. This ion is likely produced upon H-. abstraction by CH3S. from CH3SCH 2C(CH2)CO+ within the collision complex (net CH2S abstraction). The la tter reaction has not been reported for distonic radical cations with localized radical sites. Hence, the reaction must be driven by the reg eneration of the delocalized allylic radical. This proposal is support ed by the observation of CH2S abstraction for the product ion (CH3SCHC )-C-.(CH2)CO+ that also contains a delocalized radical site.