Friedel - Craft's reaction involves electrophilic substitution and electrophile attacks at the electron rich site. Presence of electron releasing substituent (like $- CH _{3}$ ) increases the electron density over benzene nucleus, and thus activates it towards electrophilic substitution. $- NO _{2}$ is a electron withdrawing group and thus, deactivates the benzene nucleus strongly. Hence, nitrobenzene does not give Friedel-Craft's reaction.