Hey Everybody, here is a good trick to keep in your back pocket if you run across an EAS question where you have something in the ortho position, but not the para.

Here is a good trick to do it: First, bromonate your benzene ring under standard condition, then sulfonate using SO3/H2SO4.  This will make the para bromo sulfonate.  Now the next substituent, our chlorine, will be directed ortho to the bromine.  We now have a trisubstituted arene ring and can remove the sulfonate unsing acidic water.  This gives us a nice route to the ortho di-halide without having to justify why we got a mixture of the ortho and para products. 

 

For more information on this, please go to organic chemistry