In free-radical chain reactions, a diatomic halogen molecule is reacted with the most reactive hydrogen atom on a carbon chain to form a halide and a haloalkane. In the case of bromination, diatomic bromine is reacted with a carbon chain to form hydrobromic acid and an alkyl halide. The first step in the reaction is initiation, or the formation of bromine radicals. These radicals can then react with hydrogens along the carbon chain through propagation to form hydrobromic acid and a carbon radical. Additionally, the carbon radicals can react with other bromine radicals to form carbon-bromine bonds. The reaction is stopped through the termination step where two radicals react with each other to diminish the concentrations of free reacting radicals. Bromine was used because it is much more selective in reaction than other halogens. For example, diatomic chlorine …show more content…
The rates of reaction are determined by the types of hydrogens present in each molecule. Aromatic hydrogens are hydrogen atoms on a benzene or ring structure. Aliphatic hydrogens are hydrogen atoms attached to a sp3 hybridized carbon that are attached to another sp3 hybridized carbon. Benzylic hydrogens are hydrogen atoms attached to a sp3 hybridized carbon that are attached to an aromatic ring structure. Compounds with benzylic hydrogens react faster that compounds with aliphatic or aromatic hydrogens. Structures with aliphatic hydrogens react slightly faster than those with only aromatic hydrogens. Additionally, secondary benzylic structures react faster than primary benzylic structures. For aliphatic hydrogen structures, tertiary hydrogens are the most reactive while primary hydrogens are the least reactive. Secondary aliphatic hydrogens react faster than primary aliphatic hydrogens, but slower than tertiary aliphatic