Freshman Organic Chemistry II with Michael McBride - 9. Pentavalent Carbon? E2, SN1, E1

Freshman Organic Chemistry II (CHEM 125B) Preliminary X-ray analysis of molecules that have been designed to favor a carbon with five bonds seemed to suggest the possibility of a pentavalent intermediate in SN2 reactions, but further analysis of these structures showed just the opposite. Boron, however, can be pentavalent in such an environment. E2, SN1 and E1 mechanisms compete with the SN2 reaction. Factors controlling E2 eliminations are illuminated by kinetic isotope effects, stereochemistry, and regiochemistry. The competition between E2 and SN2 mechanisms influence the design of synthetic schemes, including those in which carbon nucleophiles play an important role. SN1 and E1 reactions involve carbocation intermediates and thus the possibility that the carbon skeleton will rearrange. 00:00 - Chapter 1. Using X-Ray to Investigate the Possibility of a Pentavalent Carbon Intermediate 14:41 - Chapter 2. The E2 Reaction and Kinetic Isotope Effects 19:51 - Chapter 3. Stereochemistry & Regiochemistry of E2 Elimination 32:20 - Chapter 4. Strategies for Substitution in Organic Synthesis 41:39 - Chapter 5. SN1 and E1 Reactions - Kinetic Evidence for SN1 Substitution 45:09 - Chapter 6. Carbocation Intermediates: Competition and Rearrangement Complete course materials are available at the Open Yale Courses website: http://oyc.yale.edu This course was recorded in Spring 2011.