Common and important organic chemical functional groups found in biological molecules  (R -- any oganic group):

NAME GROUP EXAMPLE
hydroxyl: -OH ethanol:  CH3-CH2-OH
aldehyde: -CHO acetaldehyde:  CH3-CHO
 O
  ||
-C-H
acid: -COOH acetic acid:  CH3-COOH
 O
  ||
-C-OH
<--->
 O
  ||
-C-O-
<--->
 O-
  |
-C=O
amine: -NH2 methyl amine:  CH3-NH2
(-NH3+)
ketone: -CO- pyruvic acid:  CH3-CO-COOH
 O
  ||
-C-
ether: -O- ethyl ether:  CH3-CH2-O-CH2-CH3
ester: -COOR methyl ester of acetic acid:  CH3-CO-OCH3
 O
  ||
-C-O-R
amide: -CONH2 acetamide:  CH3-CONH2
 O
  ||
-C-NH2
sulfhydryl: -SH 2-mercaptoethanol: HO-CH2-CH2-SH
disulfide: -S-S- R-S-S-R
phenyl: phenol:  C6H5-OH, or -OH