Acetone, radical cation

This case is clearly one in which nonstatistical dynamics (indicated both by the time-dependent branching ratio and the lack of correspondence between the static symmetry of the intermediate and its branching ratio) plays an important role, despite the depth of the PE minimum in which the acetone radical cation resides. 

Vinylcyclopropane to cyclopentene rearrangement 184 Dissociation of acetone radical cation 186 The wolff rearrangement 187... 

Trajectories initiated from the vicinity of acetone radical cation showed essentially equal loss of either methyl (branching ratio 1.01 0.01). In contrast, the branching ratio observed for methyl loss in trajectories originating the TS was 1.13 0.01, which is in qualitative agreement with the experimental values of 1-1,4.24 When the trajectories were divided into time courses, with a resolution of 5fs, a unique phenomenon appeared that the newly created methyl dissociated predominantly at very short reaction time intervals. It was found that the trajectories that would lose the newly formed methyl at very short times never entered the PES minimum of the acetone radical cation. The shortest duration trajectories simply took the exit without ever attaining the equilibrium geometry of the radical cation. 

Methyl Loss from Acetone Radical Cation The loss of a methyl... 

Nummela, J. A. Carpenter, B. K. Nonstatistical dynamics in deep potential wells A quasiclassical trajectory study of methyl loss from the acetone radical cation, J. Am. Chem. Soc. 2002,124, 8512-8513. 

Unlike keto-enol tautomerism, where the enol form is thermodynamically less stable than the keto form, upon one-electron oxidation a reversal takes place and the enol radical cation is thermodynamically more stable, e.g. the gaseous acetone radical cation is 14kcalmoU less stable than its enol radical cation. Trikoupis and Terlouw have... 

Thus, the secondary C3HeO radical cations created by the McLafferty rearrangement of the molecular ions of hexan-2-one (Scheme 7) correspond to the ionized enols of acetone and not acetone radical cations, and further fragmentation may require re-ketonization . Similarly, elimination of an alkene fragment from the molecular ions of alkylbenzenes gives rise primarily to an isotoluene radical cation (Scheme 8) which differs in reactivity from the toluene molecular ion. In most cases these differences alter the details of the fragmentation mechanisms, but not the principal routes of a further fragmentation. 

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