Lesson 1
Alkene Addition Mechanisms 4
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Prof. McBride, J. Michael, CHEM 125b, Freshman Organic Chemistry II, Spring 2011, YALE Open Courses: Yale University, Chemistry (Accessed 15/09/2014), http://oyc.yale.edu/chemistry/chem-125b/lecture-11 License: Creative Commons BY-NC-SA Addition to alkenes can involve free-radical, metal-catalyzed, and stepwise electrophilic mechanisms, the last via a cation intermediate. Electrostatics can help position an attacking electrophile like H+, but bonding en route to Markovnikov addition requires orbital mixing to form the more stable cation. Stabilization of a carbocation via methide shift can compete with its trapping by solvent. The curious relative rates in stepwise addition of HCl or HBr to alkynes show that halogen substituents are both electron withdrawing and electron donating.


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