Number of compounds from the following which cannot undergo Friedel-Crafts reactions is: ________. toluene, nitrobenzene, xylene, cumene, aniline, chlorobenzene, $$m$$-nitroaniline, $$m$$-dinitrobenzene

Friedel-Crafts reactions don't work with strongly deactivated aromatic rings (those with powerful electron-withdrawing groups).

Cannot undergo Friedel-Crafts: nitrobenzene (strongly deactivated), aniline (amine complexes with AlCl₃ catalyst), m-nitroaniline (strongly deactivated), m-dinitrobenzene (very strongly deactivated).

Can undergo: toluene, xylene, cumene (all activated), chlorobenzene (mildly deactivated but can still react).

Count of those that CANNOT: nitrobenzene, aniline, m-nitroaniline, m-dinitrobenzene = 4.

The answer is $$\boxed{4}$$.