Consider the following resonance structures of aryl alkyl ethers :(i) From the above structures we find that the presence of the OR group has increased the electron density on the benzene ring and therefore the ring is said to have been activated towards incoming electrophiles.
(ii) From structures (II), (III) and (IV) we find that and the electron density has increased on C-2, C-4 and C-6, i.e., at the ortho and para positions. As a result the electrophile (E⊕) attaches itself to these e– rich sites and the –OR group is said to have directed the E⊕ to ortho and para positions.