*X for any (pseudo)halogen atom (in the related MLXZ notation, X represents a one-electron donor ligand)
*L or L for a ligand or ligands (in the related MLXZ notation, L represents a two-electron donor ligand)
*M or Met for any metal atom ([M] is used to indicate a ligated metal, ML, when the identities of the ligands are unknown or irrelevant)
*E or El for any electrophile (in some contexts, E is also used to indicate any p-block element)
*Nu for any nucleophile
*Z for conjugating electron-withdrawing groups (in the related MLXZ notation, Z represents a zero-electron donor ligand; in unrelated usage, Z is also an abbreviation for the carboxybenzyl group.)
*D for deuterium (H)
*T for tritium (H)