Functional group: An atom or group of atoms within a molecule responsible for the characteristic reactions of a particular compound

Nucleophile: A substance that donates a pair of electrons in a reaction

Electrophile: A substance that accepts a pair of electrons in a reaction

Sigma bond: A type of covalent bond formed by head-on overlap of atomic orbitals in which the majority of the electron density is in the same plane as the nuclei, the strongest type of covalent bond

Pi bond: A type of covalent bond formed by the side-by-side overlap of orbitals with the electron density concentrated above and below the plane of the nuclei

Alkyl group: A functional group of an organic molecule that only contains C and H atoms

Chiral: Describes molecules that cannot be superimposed on its mirror image

Free radical: Molecules or ions with unpaired electrons

Isomer: Compounds with the same molecular formula but different chemical structure

Substitution reaction: A reaction in which one atom or group of atoms is replaced by another atom or group of atoms

Addition reaction: A reaction in which an atom or group of atoms is added to a molecule across a double bond

Elimination reaction: A reaction in which atoms are removed from a molecule

Oxidation: A reaction in which the oxidation number is increased or the proportion of electronegative substituents in a compound is increased

Reduction: A reaction in which the oxidation number is decreased or the proportion of electronegative substituents in a compound is decreased

Hydrolysis: The addition of water to a substance to break it down

Lone pair: A pair of electrons in a molecule not shared between two atoms

Steric hindrance: The physical blockage of a particular site within a molecule by the presence of local atoms or groups of atoms

Transition state: A short-lived configuration of atoms formed during a chemical reaction that is the least stable and associated with the highest energy level on a reaction path

Intermediate: A chemical substance produced during the conversion of reactant to product

Electronegativity: The tendency for atoms in a molecule to attract a bonding pair of electrons