Bromination of Arenes

710 Words3 Pages
Bromination of Arenes This lab demonstrated the application of adding bromine to various arenes, hydrocarbons with alternating single bonds. This process, bromination, is a mechanism which treats hydrogen as a functional group. This being the case, the rate of reaction of certain arenes can be measured and compared to that of other arenes upon the addition of the bromine. The reaction occurs when the bromine radical generates from the halide diatomic molecule, using light energy. The fact that the energy needed to break the necessary bonds falls within the visible light spectrum is the basis on which the experiment is based. This brings up the issue of selectivity. For example, the bromine radical is more selective than the chlorine radical. This has to do with electronegativity. It is known that chlorine is more electronegative than bromine, and thus chlorine is more reactive, and less discriminatory as to what it will react with, thus making bromine more “selective”. Another pertinent piece of information to look at would be stability. The stability of a free radical increases as the number of carbon substituents increases. Therefore, primary is the least stable and tertiary is the most stable. Also, the more stable the free radical that is left behind, the weaker its C-H bond strength will be. The difference between the bromine and chlorine product ratios can be partially explained by the Hammond postulate, which states that species with similar energy levels also have more similar structures and react more quickly and less selectively. In the experiment, five different hydrocarbons were tested to measure the rate of reaction with the addition of bromine. Two trials were done, one with the test tubes containing the hydrocarbons and added bromine sitting directly under a lamp, and another with the test tubes in a closed, dark space. Both trials contained a

More about Bromination of Arenes

Open Document