The key difference between nucleophile and electrophile is that the nucleophile is a substance that seeks a positive centre whereas the electrophiles seek negative centres that have extra electrons.
We can name the species arising due to a charge separation as “electrophiles” and “nucleophiles”. We will discuss what is exactly a nucleophile or an electrophile in this article. Electrophiles and nucleophiles are important to initiate chemical reactions. Further, they are important to describe how the reactions proceed. In organic chemistry, we can categorize reaction mechanisms depending on the initial species (either an electrophile or nucleophile) that begins to attack the other species. Nucleophilic substitution, nucleophilic addition, electrophilic substitution, and electrophilic addition are the four major types of mechanisms describing organic reactions.
CONTENTS
1. Overview and Key Difference
2. What is Nucleophile
3. What is Electrophile
4. Side by Side Comparison – Nucleophile vs Electrophile in Tabular Form
5. Summary
What is Nucleophile?
A nucleophile is any negative ion or any neutral molecule that has at least one unshared electron pair. Nucleophile is a substance that is very electropositive, therefore, like to interact with positive centres. It can initiate reactions using the lone electron pair. For example, when a nucleophile reacts with an alkyl halide, the lone pair of the nucleophile attacks the carbon atom that bears the halogen. This carbon atom has a partial positive charge due to the difference between the electronegativity values of this carbon and the halogen atom. After the nucleophile attaches to the carbon, the halogen leaves. We call this type of reactions as nucleophilic substitution reactions.
Figure 01: A Nucleophilic Addition Reaction
There is another type of reaction which nucleophiles can initiate; we call it nucleophilic elimination reaction. Nucleophilicity tells about the reaction mechanisms; thus, it is an indication of the reaction rates. For example, if the nucleophilicity is high, then a certain reaction becomes fast, and if the nucleophilicity is low, the reaction rate is slow. Since nucleophiles donate electrons, according to the Lewis definition, they are bases.
What is Electrophile?
Electrophiles are reagents, which in their reactions seek the extra electrons that will give them a stable valence shell of electrons. Carbocations are electrophiles. They are electron deficient and have only six electrons in their valence shell. Because of this, carbocations can act as Lewis acids. They are accepting an electron pair from a nucleophile and fill the valence shell.
Figure 02: An Electrophilic Addition Reaction
Electrophiles may have a formal-positive charge, partial-positive charge, or a valance shell with an incomplete octet. Electrophilic substitution and electrophilic addition reactions are the two major reactions that electrophiles can initiate. In an electrophilic substitution reaction, an electrophile displaces an atom or group in a compound. We can see this incident mainly in aromatic compounds. For example, this is the mechanisms with a nitro group attaches to the benzene ring by displacing hydrogen. In electrophilic addition reaction, a pi bond in a molecule breaks down and a new sigma bond forms between the molecule and the electrophile.
What is the Difference Between Nucleophile and Electrophile?
A nucleophile is any negative ion or any neutral molecule that has at least one unshared electron pair whereas the electrophiles are reagents, which in their reactions seek the extra electrons that will give them a stable valence shell of electrons. Thus, the key difference between nucleophile and electrophile is that the nucleophile is a substance that seeks a positive centre whereas the electrophiles seek negative centres that have extra electrons. Moreover, we can consider nucleophiles as Lewis bases while electrophiles as Lewis acids. Hence, this is another difference between nucleophile and electrophile.
The below infographic tabulates the difference between nucleophile and electrophile as a side by side comparison.
Summary – Nucleophile vs Electrophile
Nucleophiles and electrophiles are two different forms of chemical species that have the capability of initiating different chemical reactions. The key difference between nucleophile and electrophile is that the nucleophile is a substance that seeks a positive centre whereas the electrophiles seek negative centres that have extra electrons.