Aniline does not undergo Friedel-Crafts reaction, though it contains an electron -donating group-Why ?

Explanation

Aniline (Lewis base) combines with `AlCl_3` (Lewis acid ) by donating the unshared electron pair on nitrogen, to form a complex. As a result , the N-atom of `-NH_2` group acquires a positive charge and this , being converted into an electron attracting group, decreases the electron density of the ring to such an extent that the Friedel-Crafts reaction does not occur.
`C_6H_5overset(..)NH_2+AlCl_3tounderset("Lewis acid -Lewis base complex")(C_6H_5-overset(oplus)NH_2tooverset(Theta)(AlCl_3))`