monobromination

Monobromination is the introduction of a single bromine atom into an organic molecule, in contrast to polybromination where multiple bromine atoms are incorporated. The approach and mechanism depend on the substrate and the desired position of substitution. In arenes, monobromination typically proceeds by electrophilic aromatic substitution, giving mono-brominated derivatives such as bromobenzenes. Regioselectivity is governed by directing groups and substituents on the ring, which influence ortho, meta, or para outcomes. Reaction conditions often rely on bromine in a nonpolar solvent with an appropriate catalyst or Lewis acid, with careful control of temperature and time to avoid further bromination.

For aliphatic substrates, monobromination frequently occurs through radical pathways. Alkanes can undergo bromination to yield brominated products, but these reactions often produce mixtures of mono- and polybrominated compounds. A common way to achieve greater selectivity for a single bromine atom is to use N-bromosuccinimide (NBS), which preferentially abstracts allylic or benzylic C–H bonds to form allylic or benzylic bromides under light or radical initiators. NBS is widely employed for the synthesis of allyl and benzylic bromides in various solvents.

In applications, monobrominated intermediates serve as versatile building blocks for cross-coupling reactions and further functionalization, enabling subsequent C–C or C–heteroatom bond formation. Limitations include the tendency of many substrates to undergo overbromination, the hazard and corrosivity of brominating reagents, and the need for careful control of stoichiometry and reaction conditions to obtain the desired monobrominated product.