Some crude ASCII structural diagrams for MDMA and related chemicals. See also the Lycaeum and PiHKAL.

MDMA (3,4-methylenedioxy-N-methylamphetamine):

                  NH
   O   /\   /\   / \
  / \ /--\ /  \ /   CH3
 /   ||  ||    |
CH2  ||  ||    CH3
 \   ||  ||    
  \ / \--/
   O   \/
MDA (3,4-methylenedioxyamphetamine)
                  NH2
   O   /\   /\   /
  / \ /--\ /  \ / 
 /   ||  ||    |
CH2  ||  ||    CH3
 \   ||  ||    
  \ / \--/
   O   \/
MMDA (3-methoxy-4,5-methylenedioxyamphetamine)
                  NH2
   O   /\   /\   /
  / \ /--\ /  \ / 
 /   ||  ||    |
CH2  ||  ||    CH3
 \   ||  ||    
  \ / \--/
   O   \/
        |
        OCH3
methamphetamine (N-methylamphetamine)
             NH
  /\   /\   / \
 /--\ /  \ /   CH3
||  ||    |
||  ||    CH3
||  ||    
 \--/
  \/
Bupropion (1-(3-chlorophenyl)-2-[(1,1-dimethylethyl)amino]-1-propanone; the active ingredient of Wellbutrin and Zyban)
         O    H 
        ||    N
   /\   /\   / \  /
  /--\ /  \ /   \/
 ||  ||    |    /\
 ||  ||    |   /  \  
 ||  ||    
  \--/  
   \/    
    |     
    Cl    
PEA (phenethylamine)
            NH2
  /\   /\  /
 /--\ /  \/
||  ||
||  ||
||  ||    
 \--/
  \/
dopamine (3,4-dioxyphenethylamine):
               NH2
HO   /\   /\  /
  \ /--\ /  \/
   ||  ||
   ||  ||
   ||  ||    
  / \--/
HO   \/