How to guess a transition state structure (continued)

 

·   If the structures of the reactant and product are known, can construct a model TS as a ‘midpoint’ between the two. 

 

·   For example, for the reaction H-N-C ® N-C-H, the TS model could be specified from the internal coordinates for the reactant and product. 

 

·   The H-N-C angle in the reactant is 180°, whereas it is 0° in the product.  In the TS model, therefore, a value of H-N-C = 90° could be used as a first guess. 

 

·   The bond lengths (interatomic distances) could also be chosen to be intermediate between the reactant and product.

 


 

Need to be careful in the choice of coordinates- trying to create a model TS with Cartesian coordinates would cause problems here (hydrogen between N and C!). 

 

Next: how to guess a transition state structure (continued)