Question

An electrostatic potential map of (trifluoromethyl)benzene, ${\mathbf{C}}_6{\mathbf{H}}_5{\mathbf{CF}}_3$, is shown. Would you expect (trifluoromethyl)benzene to be more reactive orless reactive than toluene toward electrophilic substitution? Explain.

Short answer

Trifluoromethyl benzene will be less reactive than toulene towards electrophilic substitution.

Step-by-step solution

Activating and Deactivating Effects

Activating groups contribute electrons to the ring making it more electron rich, stabilizing the carbocation intermediate. Deactivating groups withdraw electrons from the ring making it electron poor, thereby destabilizing the carbocation intermediate. The contribution or withdrawal of electrons by a group happens by the inductive and resonance effects.

Reactivity of trifluoromethyl benzene and toulene

Since fluorine is highly electronegative, the combined electron withdrawing effects of all the three fluorine atoms reduce the electron density in the benzene to a greater extent and the ring gets deactivated. This is shown in the electrostatic potential map. Hence trifluoromethyl benzene is less reactive than toulene towards electrophilic substitution.

The methyl group in toulene is electron activating and enhances the electron density in the benzene ring making toulene more reactive towards electrophilic substitution.