8. Solvent, Leaving Group, Bridgehead Substitution, and Pentavalent Carbon

Freshman Organic Chemistry II (CHEM 125B)

The nature of nucleophiles and leaving groups has strong influence on the rate of SN2 reactions. Generally a good nucleophile or strong base is a poor leaving group, but hydrogen-bonding solvents can alter nucleophile reactivity. Although amino and hydroxyl groups are poor leaving groups, they may be converted to groups that leave easily, even from bridgehead positions. Designing the preparation of a sugar analogue containing radioactive fluorine shows how understanding the SN2 mechanism enables PET scanning for medical imaging. Quantum mechanics suggests that the pentavalent carbon species on the SN2 reaction pathway is a transition state, not a stable structure.

00:00 - Chapter 1. Chapter 1. Nucleophilicity and the Influence of Solvent
02:34 - Chapter 2. Leaving Groups & Bridgehead Substitution
11:12 - Chapter 3. Making OH a Leaving Group
27:48 - Chapter 4. Accelerating SN2 to Support PET Scanning
44:57 - Chapter 5. Using Theory to Investigate the Possibility of a Pentavalent Carbon Intermediate

Complete course materials are available at the Open Yale Courses website: http://oyc.yale.edu

This course was recorded in Spring 2011.