Examples of Organic Reactions With Non-Statistical Dynamics

3 EXAMPLES OF ORGANIC REACTIONS WITH NON-STATISTICAL DYNAMICS 

We begin the discussion of dynamic effects with an analysis of the rearrangement of bicyclo[3.2.0]hex-2-enelto bicyclo[2.2.1]hex-2-ene 2(Reaction 8.1). Though Carpenter s MD studies of this rearrangement involved computations on semiempirical PESs, this study was the first to demonstrate the importance of dynamic effect in organic reactions. It also provides a fine example of some of the major symptoms of nonstatistical outcomes and evidence for dynamic effects. 

To probe this question, Carpenter performed direct dynamics using both the AMI and PM3 surfaces. An ensemble of initial states at 300 C was prepared about the higher energy TS (5) and trajectories were computed in the reverse direction. The principle of microscopic reversibility implies that these same trajectories that run backwards are appropriate trajectories for the forward reaction. One hundred trajectories were run on each surface for 500 fs. The trajectories fell into two 

There were four short trajectories on the PMl surface and 10 such trajectories on the AMI surface. All of these short-lived direct trajectories proceed with counterclockwise motion about the C -C bond leading exclusively to inversion about C5. No short-lived trajectory gives retention product nor do they reside in the vicinity of the diradical 4 for any appreciable time. One may consider these trajectories as following the Woodward-Hoffman allowed, concerted path, except that it occurs over a PES containing a diradical  

These direct trajectories all begin with energy in C5-C5 rotational vibration mode, with its initial motion in the clockwise direction. The trajectory simply conserves this angular momentum, continuing the clockwise rotation through 180 as C5 migrates to make the new C-C bond. 

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