Nucleophile

Nucleophile

A Nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in a reaction. Nucleophiles can be ions (such as the chloride ion, Cl-) or molecules (such as ammonia, NH3). Nucleophiles may take part in nucleophilic substitution reactions, which are of prime importance in organic chemistry.

Characteristics

Nucleophiles are characterized by the presence of lone pair of electrons and the ability to form a new bond to a hydrogen ion. The charge on the nucleophile can be negative, neutral or positive. The strength of a nucleophile is not determined by charge but by several factors including: polarizability, charge, and orbital type.

Types of Nucleophiles

There are several types of nucleophiles:

• Neutral Nucleophiles: These are nucleophiles which have a neutral charge. They do not have any extra electrons, but they have a lone pair which can be donated. Examples include water, ammonia, and alcohols.

• Anionic Nucleophiles: These are nucleophiles with a negative charge. They have an extra electron which can be donated and are thus very strong nucleophiles. Examples include: hydroxide, alkoxide, and carboxylate ions.

• Cationic Nucleophiles: These are very rare and can be found in certain organic reactions.

Nucleophilicity

Nucleophilicity refers to the affinity of a nucleophile towards a positive charge. It is often used to compare the affinity of atoms. It is affected by charge, electronegativity, and polarizability.

Nucleophile vs Base

While a nucleophile attacks atoms that are electron deficient, a base attacks atoms that are proton rich. The terms nucleophile and base are often used interchangeably in organic chemistry.

See Also

• Electrophile
• Nucleophilic substitution
• Nucleophilic addition

References

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