IB Chemistry R3.4 Electron-pair Sharing Reactions Key Definitions

The positively charged, non-aromatic intermediate formed when a benzene ring donates a pair of π-electrons to an electrophile. Its delocalized system is broken, so it is less stable than benzene.

A carbocation is a carbon atom that carries a positive charge, formed when a bond is broken heterolytically, leaving the carbon electron-deficient.

A coordination bond (also known as a dative covalent bond) forms when both electrons in the shared pair come from the same atom.

An electrophile is a species that accepts an electron pair to form a covalent bond.

In chemistry, heterolytic fission refers to the breaking of a covalent bond where both bonding electrons are transferred to one of the two bonded atoms.

A leaving group is an atom or group of atoms that detaches during a substitution reaction.

Lewis acid is a species that accepts an electron pair. It is often electron-deficient, meaning it has an incomplete octet or a positively charged center that makes it eager to gain electrons.

Lewis base is a species that donates an electron pair. It is electron-rich, often possessing a lone pair of electrons that can be shared.

A molecule or ion that donates a lone pair of electrons to a central metal ion to form a coordination bond.

When a hydrogen halide (HX) adds to an unsymmetrical alkene, the hydrogen atom attaches to the carbon with more hydrogen atoms, while the halogen attaches to the carbon with fewer hydrogen atoms.

A nucleophile is an electron-rich species that donates a pair of electrons to form a covalent bond. The term “nucleophile” originates from the Greek words nucleus (meaning core) and philos (meaning loving), indicating its affinity for positively charged or electron-deficient centers.

Nucleophilic substitution reactions occur when a nucleophile (an electron-rich species) attacks an electrophile (an electron-deficient species) and replaces a leaving group.