Kinetics and mechanisms of nucleophilic displacements with heterocycles as leaving groups. Part 19. Chemometric investigation of the simultaneous dependence of S N 2 rates on alkyl group structure and leaving group nucleofugacity

The preparation and kinetics of nucleophilic displacement are reported for four β-branched primary alkyl groups attached to neutral nucleofuges. Principal-component analysis on a set of 10 nucleophilic substitution reactions with neutral and anionic nucleofuges finds that the first principal component accounts for 70% of the variance and confirms that the tri- and penta-cyclic nucleofuges are similar to chloride ion in leaving-group activity. Partial least-squares analysis shows that the nucleophilic displacement rates for the tricyclic derivatives (2) depends on substituent shape (as measured by the Verloop parameter) rather than on size as measured by ES,. The σ* and polarizability terms are also important.