Regioselectivity in epoxide ring opening is characteristic of an organic chemistry passage subject on the MCAT, but which is a bit too abstruse to be prior required knowledge for the exam. A shift in conditions to acid catalysis shifts the regioselectivity of epoxide ring opening from less highly substituted carbon to the carbon with more aliphatic substituents. In other words, anionic nucleophiles attack the less hindered carbon, while with acid catalysis, the other carbon is favored for attack. Under acid conditions, the epoxide oxygen is first protonated, and then carbocation character develops at the carbon under attack by the nucleophile in the rate-determining step. More highly substituted carbons can better support positive charge because of the electron releasing character of aliphatic substituents.

The WikiPremed MCAT Course is a comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum. Please read our policies on Privacy and Shipping & Returns.  Contact Us. MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course. WikiPremed offers the customers of our publications or our teaching services no guarantees regarding eventual performance on the MCAT.

Creative Commons License
WikiPremed is a trademark of Wisebridge Learning Systems LLC. The work of WikiPremed is published under a Creative Commons Attribution NonCommercial ShareAlike License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions.