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E1 Reaction: Stereochemistry and Regiochemistry

E1 Reaction: Stereochemistry and Regiochemistry

One of the critical aspects of the E1 reaction mechanism, as also observed in E2, is the regiochemistry, with multiple regioisomers obtained as products. In the example discussed, the presence of water as a weak base favors elimination over substitution to generate two alkenes. Given that alkenes’ stability increases with the number of alkyl groups across the double bond, typically, E1 reactions lead to the Zaitsev product, for this is more substituted and stable than the Hofmann product.

Regioselectivity of Electrophilic Additions-Peroxide Effect

Regioselectivity of Electrophilic Additions-Peroxide Effect

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.

E2 Reaction: Stereochemistry and Regiochemistry

E2 Reaction: Stereochemistry and Regiochemistry

Elimination reactions of alkyl halides can yield one or more alkenes depending on the specific regiochemical and stereochemical considerations. While the regiochemistry of the reaction governs the location of the double bond in the product, the stereochemical requirements often influence the geometry.
When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major...

Reactions at the Benzylic Position: Oxidation and Reduction

Reactions at the Benzylic Position: Oxidation and Reduction

The benzylic position describes the position of a carbon atom attached directly to a benzene ring. Benzene by itself does not undergo oxidation. In contrast, the benzylic carbon is quite reactive in the presence of strong oxidizing agents such as KMnO4 or H2CrO4. Therefore, alkylbenzenes are readily oxidized to benzoic acid, irrespective of the type of alkyl groups.

Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration

Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration

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.

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

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...

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Related Experiment Video

Updated: Feb 28, 2026

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy

Published on: February 20, 2020

Zr-Site Lewis Acidity Determines Terpenoid Reduction Selectivity.

Kinga Gołabek¹, Svetlana Kurucová¹, Juan Francisco Miñambres¹

¹Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Albertov 6, Prague, Praha 128 43, Czech Republic.

ACS Catalysis

|February 26, 2026

Summary

Lewis acid zeolites, specifically Zr-beta, show distinct catalytic activities based on "open" versus "closed" Lewis acid sites. "Closed" sites favor Meerwein-Ponndorf-Verley reduction, while "open" sites promote cyclization, enabling targeted catalyst design.

Keywords:

MPV reduction Zr-zeolite acetone adsorption citronellal citronellol isopulegol lewis acidity transfer hydrogenation

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Published on: January 17, 2020

Area of Science:

Catalysis
Materials Science
Organic Chemistry

Background:

Lewis acid zeolites, particularly Al-free Zr and Sn silicates, are effective catalysts for Meerwein-Ponndorf-Verley (MPV) reduction of carbonyl compounds.
The precise role of different types of Zr sites (open vs. closed) in Zr-zeolites for chemoselective reduction and competing reactions remains unclear.
Understanding site-specific catalysis is crucial for optimizing reactions like citronellal reduction, which can yield multiple products.

Purpose of the Study:

To correlate the characteristics of Lewis acid sites in Zr-substituted beta and MFI zeolites with their catalytic selectivity.
To elucidate the role of

Main Methods:

Fourier transform infrared (FTIR) spectroscopy using deuterated acetonitrile and acetone to probe and differentiate between

Main Results:

Zr-beta zeolites with a high concentration of

Conclusions:

The Lewis acidity of Zr sites in zeolites dictates selectivity in terpenoid reduction.
Weaker Zr-beta "closed" sites selectively catalyze MPV reduction of citronellal to citronellol.
Stronger Zr-beta "open" sites preferentially catalyze intramolecular carbonyl-ene cyclization to isopulegol.