Markovnikov’s Rule#

Investigate the stability of reactions using Markovnikov’s rule.


Build a propene molecule and optimize its geometry. Compare the relative energy of bromine-hydrogen substitution at either the 1-carbon or 2-carbon of the carbon-carbon double bond. Which of these two bromopropane compounds will be the major product of a propene bromination reaction?


Results of relative energies expressed in kJ/mol (need confirmation in literature).

Force field

Intermediate primary carbocation (1’)

Intermediate secondary carbocation (2’)

1-bromopropane (1)

2-bromopropane (2)
















UFF data is considered in this case, the secondary carbocation intermediate requires less energy (2’) than the primary carbocation intermediate (1’) (resp. 3.6 vs 4 kJ/mol). So compound (2) will be the major form. This is called the Markovnikov’s rule: “the major product of the addition of HX (where X is some atom more electronegative than H, the bromine in our case) to an alkene (here the propene) has the hydrogen atom in the less substituted position and X in the more substituted position”. Mechanisms which avoid the carbocation intermediate such as the presence of dialkyl peroxides will reverse the reaction result and compound (1) becomes the major product (Anti-Markovnikov rule).

See also#

Alkene Isomers

Further reading#

Markovnikov’s rule (wikipedia)