Lecture 07 - Nucleophilic Substitution Tools - Stereochemistry, Rate Law, Substrate, Nucleophile, Leaving Group. SN2 substitution provides an example of establishing the mechanism of a chemical reaction by disproving all the alternatives.
Five general pathways are envisioned (two-step involving either pentavalent or trivalent carbon intermediates, and one-step). They can be discriminated by applying a variety of experimental tools including stereochemistry (Walden inversion),
rate law (second order and pseudo first order), and the variation of rate constant with changes in the substrate (steric hindrance and ring strain), and with changes in nucleophile or leaving group. Classic experiments by Kenyon and Phillips and
by Bartlett and Knox established the nature of Walden inversion.
(from oyc.yale.edu)
1. "Proving" a Mechanism by Imagining and Disproving All the Alternatives
[00:05:59]
2. Kenyon and Phillips Pinpoint Backside Attack in Nucleophilic Substitution
[00:18:53]
3. Using Kinetics to Study Mechanisms - Rate Law
[00:25:44]
4. Rate Constant - The Influence of Substrate Structure
[00:48:27]
5. Rate Constant - The Influence of Nucleophile and Leaving Group
References
Lecture 7 - Nucleophilic Substitution Tools
Instructor: Professor J. Michael McBride. Resources: Professor McBride's website resource for CHEM 125b (Spring 2011). Transcript [html]. Audio [mp3]. Download Video [mov].