Directing Effects on Aromatic Compounds

     The terms ortho, para, and meta are used in organic chemistry to explain the regiochemistry of

heteroatoms as they are substituted on the ring.  The following molecular structures depict the ortho,

para, and meta positions.
 

Ortho Position                    Para Position                    Meta Position
                        Ortho                                      Para                                 Meta
                 The ether oxygen is                    The ether oxygen              The carbon-carbonyl bond
                 a sufficient ortho                         is also a sufficient para     acts as a meta director and
                 director and directs                     director and directs           directs chlorine to the meta
                 the chlorine atom ortho.               chlorine para.                   position.

     The directing effects are based only with respect to the director (the atom on the ring that directs

the other added substituents.  In our example, the ether (~O-CH2-COOH) directs the substituents (in

this case chlorine) to the ortho and para positions. Directors are classified as the following:  Strongly

activating ortho, para directors; Moderately activating ortho, para directors; Weakly activating ortho,

para directors, Weakly deactivating ortho, para directors; and Moderately and strongly deactivating

meta directors.  A table consisting of the different substituent directors and their directing effects

follows:
 

Strongly activating; ortho, para directors
            
 
 
Moderately activating; ortho, para directors
       
 
 
Weakly activating; ortho, para directors
        
 
 
 
Weakly deactivating; ortho, para directors
               
 
 
 
Moderately and strongly deactivating; meta directors
                        
 
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