Regioselective Reaction
Regioselective Reaction - Related Videos
04:38
Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions
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2022
Contiguous bisaziridines containing non-activated and activated aziridines were synthesized by asymmetric organocatalytic aziridinations and then subjected to chemoselective ring-opening reactions under acidic or basic conditions. The non-activated aziridine ring opens with less reactive nucleophiles under acidic conditions, whereas the activated aziridine ring opens with more reactive nucleophiles under basic conditions.
02:35
Regioselectivity of Electrophilic Additions-Peroxide Effect
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2023
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination. In the first initiation...
02:36
Regioselectivity and Stereochemistry of Hydroboration
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2023
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction. Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry. The observed preference in...
01:33
Regioselective Formation of Enolates
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2023
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are more stable. But the energy required to form kinetic enolates is less. This regioselectivity in enolate formation...
02:34
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
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2025
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate. The reaction proceeds with the slow protonation of an alkene by a hydronium ion to form a carbocation, which is the rate-determining step. The reaction involving a tertiary carbocation intermediate is faster than a reaction proceeding through a secondary or primary carbocation. This can be justified by comparing their...
FAQs
The preferred site reflects the combined effects of steric hindrance, electronic effects, reagent behavior, and reaction conditions. A position may become more favorable when it is less crowded, responds more effectively to the reagent, or follows a lower-energy pathway under the selected conditions. Considering these factors together helps explain why one constitutional isomer predominates.
When multiple positions are available, competing pathways do not necessarily have equal energetic favorability. Small differences caused by molecular crowding, electronic influences, reagent behavior, or conditions can make one pathway preferred. The resulting product distribution affects how easily chemists obtain the desired constitutional isomer and how much unwanted material must be removed.
Reaction conditions can alter which competing pathway is energetically favored, changing the relative formation of constitutional isomers. Because conditions work together with steric effects, electronic effects, and reagent behavior, a suitable choice can improve preference for the desired position. This control can reduce byproducts and simplify purification during organic synthesis.
In addition, substitution, and elimination reactions, more than one position may offer a route to product formation. Regioselectivity helps identify which placement of newly introduced or rearranged functionality is favored in each reaction class. Recognizing the possible positional outcomes allows chemists to plan transformations that produce a more useful molecular structure.
A practical approach begins by identifying the positions that could react and the constitutional isomers each position could produce. Chemists then consider steric hindrance, electronic effects, reagent behavior, and conditions to favor one pathway. Selecting the route with the strongest expected preference can reduce unwanted products and make purification more straightforward.
Researchers can assess whether the transformation preferentially produced the intended constitutional isomer and whether competing products were sufficiently reduced. A stronger preference generally supports cleaner product mixtures, while weaker preference can increase purification demands. These outcomes help determine whether a synthetic route is efficient enough for constructing more complex molecules.
The position at which a functional group is introduced can determine the structure of a molecule used in pharmaceutical or materials research. Regioselective planning helps control that placement during multistep organic synthesis, limiting unwanted constitutional isomers. Better structural control can support efficient routes, reduce purification effort, and improve access to targeted complex molecules.