Synchronous Conrotatory Motion

When the total intramolecular energy increases ( tot 62 kcal/mol), the reactive trajectories are more numerous. Below we analyze in detail the set of trajectories for Efot - 62 kcal/mol (see Fig. 12). Depending on the value of several distinguishable motions are observed  

4 kcalfmol rot 35.2 kcalfmol within these limits the trajectories are again reactive (see Fig. 12g) and of the same type as that pictured in Fig. 11. As previously, each terminal group rotates by only 180°. It should be emphasized that this second reactive band of initial rotational energies is much more narrow than the 

A long time ago. Wall and Porto have mentioned the existence of upper energy bounds for H + Hj coUinear reactions. More recently, Wright et have observed quite similar 

The results presented in this section all depend strongly on the assumption which allowed us to terminate the trajectories. For instance, certain reactive trajectories, if they were free to go on, could come back to the startii point of the reaction. Conversely, certain non-reactive trajectories, after the first process of ring opening and closure, could yield a cyclopropane molecule possessing a more suitable amount of CH2 vibration energy and the isomerization reaction could now be possible (Fig. 12a). Furthermore, the treatment of the dynamical problem in its full dimen-sionality might well make the unreactive r on between the two reactive bands disappear. 

For total intramolecular energies greater than 62 kcal/mol, ( °ot = 63,64, 65 kcal/mol), the two reactive bands of initial rot values still exist (see Fig. 13a) and even become larger and larger with increasing This is due to the fact 

---

Fig. 7. Two-dimensional potential energy surface and static reaction path for the synchronous conrotatory motion of the terminal methylene groups. 2 a represents the value of the carbon ring angle. The abcissa gives the common value of both rotational angles 6 = dj = dj. TS denotes the position of a transition state. The energies are in kcal/mol...

Five different values of have been studied, namely 61, 62,63, 64 and 65 kcal/mol. For tot = 61 kcal/mol, the only available chatmel is the synchronous conrotatory motion (transition state at 59.8 kcal/mol). For > 62 kcal/mol, the rotation of a single group (transition state at 61.6 kcal/mol) and the concerted disrotatory motion (transition state at 61.9 kcal/mol) both become feasible motions, at least in principle. For each value of jEtot, j rot has been varied stepwise from 2 to 50 kcal/mol, with a step of 2 kcal/mol. In addition, for given values of E o and has been varied from 45° (conrotatory motion, ie. antisymmetric vibra-... 

Fig. 1.19. Section of the PES of the XLVII-XLIIa reaction along the MERP for synchronous conrotatory motion of the methylene groups. Assignments of the angles a and 6 6 = = 62) are given...

---