Polar Addition to C=C Group: Why Is Anti-Markovnikov Hydroboration–Oxidation of Alkenes Not "Anti-"?

Predrag-Peter Ilich, Lucas S. Rickertsen, and Erienne Becker

Division of Molecular and Life Sciences, Loras College, Dubuque, IA 52001

Abstract

For 137 years Markovnikov's rule has been extensively used in organic chemical education and research to describe the regioselectivity in electrophilic addition reactions to alkenes and alkynes. When the structures of the final reaction products are used as reference, the rule requests that certain polar addition reactions be termed anti-Markovnikov. We use first principles thermodynamic calculations to analyze six polar addition reactions to alkenes, expected to be of either Markovnikov or anti-Markovnikov regioselectivity. Our results show no difference between the two reaction types: in each case the alkene atomic charges and the form of the intermediate completely determine the course of the overall reaction and the form of the predominant final product. We redefine this type of regioselectivity and propose that teaching of organic chemistry should be based more on robust and portable concepts such as energy difference and atomic charge than on historical labels.

Journal of Chemical Education, 2006, 83, 1681                       Full text (PDF)

-- SiripornJu - 08 Mar 2007