All About Chemistry... 2011 and beyond

CHEM 125A: FRESHMAN ORGANIC CHEMISTRY II - Lecture 11 - Professor J. Michael McBride

Carbocations and the Mechanism of Electrophilic Addition to Alkenes and Alkynes

Substitution stabilizes alkenes, and addition of acids is thermodynamically favorable in acidic media.  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.  Relative cation stability can be understood in terms of hyperconjugation, hybridization, and solvation or polarizability. 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.

Social Networking

Please recommend us on Facebook, Twitter and more:

Other social media tools


Tell us what you think of Chemistry 2011 -- we welcome both positive and negative comments. Have any problems using the site? Questions?

About us

Chemistry2011 is an informational resource for students, educators and the self-taught in the field of chemistry. We offer resources such as course materials, chemistry department listings, activities, events, projects and more along with current news releases.

Events & Activities

Are you interested in listing an event or sharing an activity or idea? Perhaps you are coordinating an event and are in need of additional resources? Within our site you will find a variety of activities and projects your peers have previously submitted or which have been freely shared through creative commons licenses. Here are some highlights: Featured Idea 1, Featured Idea 2.

About you

Ready to get involved? The first step is to sign up by following the link: Join Here. Also don’t forget to fill out your profile including any professional designations.

Global Partners