Markovnikov's Rule
Markovnikov's Rule - Related Videos
02:20
Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
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2026
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others. The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
02:55
Exceptions to the Octet Rule
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2020
Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories: Odd-electron molecules have an odd number of valence electrons and therefore have an unpaired electron. Electron-deficient molecules have a central atom with fewer electrons than needed for a noble gas configuration. Hypervalent molecules have a central atom that has more electrons than needed for a noble gas configuration. Odd-electron...
03:02
The Aufbau Principle and Hund's Rule
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2020
To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and continuing across the periods of the periodic table, we add one proton at a time to the nucleus and one electron to the proper subshell until we have described the electron configurations of all the elements. This procedure is called the aufbau principle, from the German word aufbau (“to build up”). Each added electron occupies the subshell of...
02:36
Lewis Symbols and the Octet Rule
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2020
Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a model called the Lewis model that simplified the depiction of chemical bond formation and provided straightforward explanations for the chemical bonds seen in most common compounds. Lewis Model The Lewis model depicts chemical bond formation by the sharing or transfer of valence electrons, which helps to attain a stable electron...
01:17
Radical Anti-Markovnikov Addition to Alkenes: Mechanism
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2025
The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps. The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
FAQs
The favored pathway places the developing positive charge in the arrangement that forms the more stable carbocation intermediate. This stability helps determine which alkene carbon receives hydrogen and which receives the other part of the reagent. As a result, the major product reflects the relative substitution of the possible intermediate structures.
An unsymmetrical alkene has two nonequivalent carbon atoms, so addition can occur in two constitutional orientations. Markovnikov's rule compares these alternatives by considering the hydrogen content of each alkene carbon and the substitution of the resulting intermediate. That comparison predicts which orientation should dominate rather than treating both pathways as equally likely.
Radical reaction conditions and certain catalysts can change the usual regioselective outcome. Under those circumstances, the reaction may favor an anti-Markovnikov product rather than the orientation predicted from the more stable carbocation pathway. Therefore, applying the rule requires attention to the reaction conditions, not only to the alkene structure.
First identify the two carbon atoms of the unsymmetrical alkene and compare how many hydrogen atoms each already bears. Place hydrogen on the carbon with more hydrogen atoms, then assign the other component of the polar reagent to the more substituted carbon. Finally, check whether radical conditions or a catalyst could reverse that preference.
The rule provides an early prediction of which regioisomer, or connectivity arrangement, is likely to form as the major product in an alkene addition. Chemists can use that forecast when selecting an addition reaction and designing a synthetic route, reducing uncertainty about where new atoms will be incorporated into the target structure.
It connects the observed product distribution with the reaction mechanism and the relative stability of possible intermediates. If the major product follows the usual orientation, the result is consistent with the expected polar pathway. If an alternative orientation appears, radical conditions or catalytic effects provide important context for interpreting the outcome.