Electrophilic Addition Reactions of Alkenes

When a molecule accepts electrons from other compounds, it is termed as electrophiles. Whereas, if electrons are donated by a component, then this entity is said to be the nucleophile. Electrophilic addition mechanism is a chemical reaction between a nucleophile and an electrophile, adding to triple or double bonds. 


To be more precise, an electrophilic addition reaction is the tendency to combine and react with chemical substances that possess a donatable electron pair (‘electron lover’). This is an interesting and important phenomenon in the study of organic chemistry. Thus, we will learn about the electrophilic addition to alkenes and the same with oxidizing agents. 


Before learning about the electrophilic addition reaction mechanism, let us understand what alkenes are. Present in the group of unsaturated hydrocarbons, Alkenes are elements that have a minimum of 1 double bond with at least 1 molecule. Additional products are formed from alkenes through pi electrons, where an electrophile attacks a carbon dioxide double bond. Hence the term electrophilic addition reactions of alkenes.


Electrophilic Addition Reactions of Alkenes

As we are about to move in-depth with the addition of alkenes through an electrophilic reaction, it is important to know the 2 other ways this process happens. They are namely ozonolysis and oxidation reactions (particularly with alkenes). Common examples for electrophilic addition reactions with hydrogen halides include hydrogen chloride and hydrogen bromide. 


It can happen through the procedure of Free Radical Mechanism as well. Free radical mechanism reactions follow the hierarchy of Chain Initiation, Chain Propagation and Chain Termination in the free radical group of compounds (reaction with stable molecules). 


The widely accepted order of hydrogen halide is HI > HBr > HCl. symmetrical alkenes (double bonds have the same ligands) such as ethene are easily predictable in their end products, as compared to non-symmetrical like propene (double bonds have a varied count of ligands) alkenes. This phenomenon is also sometimes referred to as Markownikoff's or Markovnikov rule.


Markovnikov Rule for Electrophilic Addition Reaction

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According to the Markovnikov rule, considering the negative part of an adding molecule, it will get linked to that 1 carbon atom that already has a fewer count of hydrogen atoms.


The Oxidation Reaction of Alkenes

When alkenes get oxidized, it leads to the production of alcohols and ketones. Oxidation reactions are also termed as the Baeyer test. 


Let us consider an example with potassium permanganate (KMnO₄). When potassium permanganate, in an aqueous and cool state, is used in the oxidation process of alkenes, this will help in the formation of vicinal glycols.


Oxidation Reaction Of Potassium Permanganate

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Note that an oxidising agent like Potassium Permanganate and the presence of a cold condition is necessary for oxidation reactions to take place.

FAQ (Frequently Asked Questions)

1. As per the Markovnikov’s rule, in which Carbon will the Electrophile Attack?

The electrophile will attack the less substituted carbon molecule whereas the most substituted one is taken over by a nucleophile.

2. List out some of the Electrophilic Addition Reactions with Alkene Reagents.

The Prins reaction, Hydroboration-oxidation reactions (using Diborane), Oxymercuration reactions to form water and mercuric acetate, Hydration reactions (H2O), Hydrogenation reactions, Hydrohalogenations (HX) and di-halo addition reactions (X2) are some of the common electrophilic addition reactions of alkene reagents.

3. Is an Electrophile Positive in Ion Charge?

Considering the aspect of an electrophile getting attracted to negatively charged ion, that is a nucleophile, an electrophile can be regarded to have a positive charge completely or at least slight the amount for achieving the opposite charge attraction.

4. What is an Additional Reaction in Organic Chemistry?

An additional reaction in organic chemistry is a process where the individual molecules bond together with another compound to form a single bigger unit. Not even a single atom is lost from the structure of the original molecule since they all join together as 1 big compound.

5. Why is the Additional Reaction of Hydrogen and Fluorine Said to be the Slowest?

The addition reaction of hydrogen and fluorine is said to be the slowest because of the property of its toughness in the H-F bond. The bond between Hydrogen (H) and Fluorine (F) is difficult to break as compared to other halogens in the periodic table. This makes the complete addition reaction of H-F slower than the rest.