Final answer:
The reaction of 1-bromo-4-methylbenzene with NH₃ results in the formation of 4-methylbenzenamine (4-methyl-aniline), through a nucleophilic aromatic substitution mechanism.
Step-by-step explanation:
The reaction of 1-bromo-4-methylbenzene with NH₃ (ammonia) is an example of a nucleophilic substitution reaction, specifically an aromatic nucleophilic substitution (SNAr). Ammonia acts as a nucleophile and can replace the bromine atom in 1-bromo-4-methylbenzene to form 4-methylbenzenamine (4-methyl-aniline) as the principal product. This reaction may proceed under certain conditions such as elevated temperatures and the presence of a base, and it may also compete with elimination reactions depending on the reaction conditions.
The mechanism involves the attack of the lone pair of electrons from the ammonia molecule on the bromine-substituted carbon of the benzene ring, displacing the bromide ion. Since we are dealing with an aromatic compound, the benzene ring needs to temporarily lose its aromaticity during the reaction, which generally requires more harsh conditions compared to aliphatic nucleophilic substitutions.
The product is named by identifying the benzene ring with an amino (NH₂) group as aniline, and since the methyl group is at the fourth position, the resulting compound is called 4-methylbenzenamine or 4-methyl-aniline. This newly formed compound belongs to the class of aromatic amines, which are important intermediates in the chemical industry, particularly for the synthesis of dyes, drugs, and polymers.