An electrophile is a chemical species that accepts an electron pair and forms bonds with nucleophiles. Electrophiles are Lewis acids because they accept electrons. Most electrophiles are positively charged, have a partial positive charge on an atom, or have an atom without an octet of electrons.
Addition and substitution reactions are the most common interactions between electrophiles and nucleophiles. Cations like H+ and NO+ polarised neutral molecules like HCl, alkyl halides, acyl halides, and carbonyl compounds, polarizable neutral molecules like Cl2 and Br2, oxidizing agents like organic peracids, chemical species that don't satisfy the octet rule like carbenes and radicals, and some Lewis acids like BH3 and DIBAL are all popular electrophiles in organic syntheses.
They are electron-deficient and are attracted to electrons.
They can either have a positive or a negative charge.
Electrons attack atoms with a lot of electrons, including carbon-carbon double bonds.
The density influences electron movement, which generally occurs from a high-density to a low-density region.
Electrophilic addition and electrophilic replacement reactions should be favored.
Since they accept electrons, they are also known as Lewis acids.
In electrophilic substitution and addition reactions, electrophiles are involved.
This article will study what is electrophile and electrophile examples in detail.
Electrophilic Reagent Examples
1. Addition of Halogens
In halogen addition reactions, these occur between alkenes and electrophiles, most commonly halogens. The use of bromine water to titrate against a sample to determine the number of double bonds present is a common reaction.
C2H4+ Br2 → BrCH2CH2Br
The electrophilic Br-Br molecule forms a -complex with the electron-rich alkene molecule.
Bromine acts as an electrophile and the alkene acts as an electron donor. With the release of Br, the three-membered bromonium ion 2 with two carbon atoms and a bromine atom emerges.
The assault of Br from the backside opens the bromonium ion. The vicinal dibromide has an antiperiplanar configuration as a result of this reaction. When other nucleophiles like water or alcohol are present, they can attack 2 and create alcohol or ether.
2. Addition of Hydrogen Halides
In hydrohalogenation, hydrogen halides such as hydrogen chloride (HCl) are added to alkenes to create alkyl halides. The reaction of HCl with ethylene, for example, produces chloroethane. In comparison to the halogen addition above, the reaction proceeds through a cation intermediate. The following is an example:
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Proton (H+) adds to one of the carbon atoms on the alkene to form cation 1 (by acting as an electrophile).
The adducts 2 and 3 are formed when the chloride ion (Cl) interacts with cation 1.
Many electrophiles are optically stable and chiral. Optical purity is typically a characteristic of chiral electrophiles. The fructose-derived organocatalyst used in Shi epoxidation is one such reagent. The catalyst will epoxidate trans-disubstituted and trisubstituted alkenes with high enantioselectivity. Until continuing in the catalytic cycle, the Shi catalyst, which is a ketone, is oxidised to the active dioxirane form by stoichiometric oxone.
Given below is the Electrophiles List-
The different types of electrophiles can be classified as:
1. Positively Charged Electrophiles:
H+, SO3H+, NO+, NO2+, X+, R+ , C6H5N2+
2. Neutral Electrophiles: These showcase electron deficiency.
(a) All Lewis acids: BF3, SO3 , FeCl3 , AlCl3 , BeCl2 , SnCl2 , SnCl4 ,ZnCl2.
(b) The neutral atom that accepts electrons from the substrates :
R *COCl, R – * Mg – X, *I – Cl, CH3 – *CN, R*–Cl, R*–O
Which is an Electrophile?
Although the hydrogen ion has a positive charge, it does not qualify as an electrophile because it has absolute empty orbitals in its outer shell.
The ammonium ion, on the other hand, does not have any empty orbitals to draw electrons. As a result, ammonium ions are not considered electrophiles.
Did You Know?
In the presence of superacids, super-electrophiles are characterised as cationic electrophilic reagents with greatly enhanced reactivities. George A. Olah was the first to identify these compounds. By proto-solvation of a cationic electrophile, super-electrophiles form as a doubly electron-deficient super-electrophile. When mixed with hydrofluoric acid, a mixture of acetic acid and boron trifluoride can extract a hydride ion from isobutane through the formation of a superacid from BF3 and HF, as Olah discovered. The [CH3CO2H3]2+ dictation is the responsible reactive intermediate.
This is all about electrophile, a chemical species, and its features. Focus on the examples and explanations given in this article to develop your conceptual foundation.