R-COOH
Carboxy-
R-SO3H
Sulfo-
R-CO-O-CO-R'
Anhydride
R-CO-X
Halocarbonyl-
R-CN
Cyano-
R-CO-H
Formyl-
R-CO-R'
Oxo-
R-OH
Hydroxy-
Ar-OH
R-SH
Sulfanyl-
R-NH2 (R2)
Amino-
R-C=N-R'
Imino-