8. Finding Transition States and Barrier Heights: First Order Saddle Points#
So far, you have already considered several systems that did not reside in a minimum of the potential energy surface. Both the bond breaking in the dissociation of H\(_2\) as well as the internal rotation of butane were examples of off-equilibrium processes, where the system moves from one equilibrium conformer, i.e. from one minimum, to another. It is intuitively clear that the likelihood of two equilibrium conformers to be transformed into each other by moving along some random path is negligible, and different methods have been established to find reasonable paths for such transitions. A frequently used approach is transition state theory, which is concerned with finding a realistic path between potential energy minima. In this set of exercises, you will search for the transition state for a the cyclisation of a deprotonated chloropropanol to propylene oxide, and you will find the minimum energy path that connects reactants to products via this transition state.
🎯 Learning goals
Understand how to navigate the PES to transition states
Visualize chemical reactions
📖 Chapter in script
Not in script but of practical relevance
📚 Resources
Frank Jensen - Computational Chemistry Ch12.8 p.416ff