Light
A substitution reaction is a type of chemical reaction where one functional group in a molecule is replaced by another functional group. It's common in organic chemistry and plays a crucial role in the synthesis of many compounds.
An electrophile is a reagent attracted to electrons that participates in chemical reactions by accepting an electron pair.
A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to reaction mechanisms.
A leaving group is an atom or group that can depart with an electron pair, resulting in the formation of a cation or positive charge on the residue.