Definition of substituent in US English:



  • An atom or group of atoms taking the place of another atom or group or occupying a specified position in a molecule.

    • ‘Under rigorous conditions benzene will undergo substitution for one of its hydrogen substituents, by a process called electrophilic aromatic substitution.’
    • ‘In an interstitial solid solution, substituent atoms or ions are added to void spaces (interstitial sites) between normal atomic sites.’
    • ‘These compounds differ in the level of oxidation of the flavane nucleus and in the number and position of hydroxyl, methyl, and methoxyl substituents.’
    • ‘Other substituents coax beta-peptides into antiparallel hairpin and sheetlike structures.’
    • ‘Any groups attached to the main chain are called substituents, they are there in place of hydrogen atoms.’


Late 19th century: from Latin substituent- ‘standing in place of’, from the verb substituere (see substitute).