Phase-space transition states structure

In a recent study, Sakic and Vrcek investigated prereactive complexes in the chlorination (with Cy of benzene, triazine, and tetrazine both in gas phase and in an apolar solvent (CCl ) [66]. Using a stochastic search methodology, they were able to systematically investigate the configurational space by which Cl can approach the aromatic x-system of benzene. With this methodology, they also find a number of new addition products and transition state structures. They could however not find the a-complex of this system, neither in gas phase nor in CCl, without a counterion, like BF or AlCl ", in close contact... 

Another interesting feature of the solid state structure is the long range packing of the Ln(btsa)3 molecules (Fig. 9). The presence of large hexagonal spaces within the crystal lattice might induce a facile phase transition, e.g., reorientation of the molecules in the crystalline lattice [115] and inclusion of solvent molecules [99b, 108], and therefore be responsible for the lack of quality of the solid state structure determinations. 

The Davis-Gray theory teaches us that by retaining the most important elements of the nonhnear reaction dynamics it is possible to accurately locate the intramolecular bottlenecks and to have an exact phase space separatrix as the transition state. Unfortunately, even for systems with only two DOFs, there may be considerable technical difficulties associated with locating the exact bottlenecks and the separatrix. Exact calculations of the fluxes across these phase space structures present more problems. For these reasons, further development of unimolecular reaction rate theory requires useful approximations. 

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