Lecture 30 - Oxidation States and Mechanisms. A difficult exam question shows how visible and NMR spectroscopy related to long-term misassignment of the structure for the triphenylmethyl dimer.
Evidence from 1970 shows that Friedel-Crafts propylation involves an SN2 mechanism, not a protonated cyclopropane. Assigning oxidation states from -4 to +4 to the carbon atoms of proposed starting material
and product allows choosing whether a reagent that is oxidizing or reducing or neither is appropriate. Beyond belonging to the appropriate redox class, the reagent must have an appropriate mechanism.
Alcohol oxidations by elemental bromine and by Cr+6 reagents are shown to involve familiar substitution, elimination, and addition mechanisms. Mechanistic understanding allows adjusting conditions to make oxidation selective.
(from oyc.yale.edu)
Lecture 30 - Oxidation States and Mechanisms
Time
Lecture Chapters
[00:00:00]
1. Exam Question on NMR, Color, and Triphenylmethyl Dimerization
[00:11:15]
2. Evidence Against Protonated Cyclopropane in Friedel-Crafts Propylation
[00:16:30]
3. Carbon Oxidation States from -4 to +4
[00:32:22]
4. Mechanism of Alcohol Oxidation by Bromine
[00:38:30]
5. Mechanism of Alcohol Oxidation by Cr+6
References
Lecture 30 - Oxidation States and Mechanisms
Instructor: Professor J. Michael McBride. Resources: Professor McBride's website resource for CHEM 125b (Spring 2011). Transcript [html]. Audio [mp3]. Download Video [mov].