Neopentyl bromide reacts with benzene under Friedel-Crafts conditions to give mainly

In this step, neopentyl bromide reacts with a Lewis acid, such as aluminum chloride (AlCl3) under Friedel-Crafts reaction conditions. The Lewis acid coordinates to the bromine atom, which weakens the carbon-bromine bond and facilitates the formation of the neopentyl carbocation intermediate. The reaction can be written as: \[ R-\text{Br} + AlCl_3 \rightarrow R^+ + \text{AlCl}_4^– \] Where R is neopentyl group.

In the second step, the carbocation electrophile reacts with the benzene ring via an electrophilic aromatic substitution reaction. The electron-rich π-system of the benzene ring acts as a nucleophile and attacks the positive carbon atom in the carbocation intermediate, forming a new carbon-carbon bond. This attack generates a positively charged cyclohexadienyl cation intermediate. The reaction can be expressed as: \[ C_6H_6 + R^+ \rightarrow [C_6H_6R]^+ \] Where R is neopentyl group and '+' indicates the positive charge on the carbon where the electrophile attached itself.

In the final step, a base (for example, Cl– or AlCl_4–) abstracts a proton from the carbon atom adjacent to the one with the positive charge in the cyclohexadienyl cation intermediate. This step restores the aromaticity of the benzene ring, giving us neopentylbenzene as the main product. The reaction can be written as: \[ [C_6H_6R]^+ + B^- \rightarrow C_6H_6R + H^\text{+}B^- \] Where R is the neopentyl group, B- is the base, and '+' indicates the positive charge on the carbon where the electrophile was attached. As a result, we have demonstrated the reaction mechanism for neopentyl bromide reacting with benzene under Friedel-Crafts conditions to form mainly neopentylbenzene, which involved the formation of a carbocation electrophile, electrophilic attack onto the benzene ring, and the restoration of aromaticity through the loss of a proton.