In the computed catalyzed pathway, the nucleophilic substitution is effectively broken into two discrete steps (Fig. ). Complexation of 1g to ion pair 10 results in chloride binding to the thiourea and association of the phosphonium ion to the cation-binding domain. Remarkably, the geometrical features of the phosphonium chloride in 1gꞏ10 are very similar to those in 10', i.e. the chloride is positioned in a nearly optimal pre-transition-state geometry (Fig. ). Thus, catalyst 1g can be seen as effectively turning the high-energy non-stationary point 10' on the uncatalyzed path into a relatively stable ground-state complex 1gꞏ10.