Cyclohexane Synthesis Lab

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Discussion The experiment conducted in lab was the bromination of arenes. Arenes are aromatic hydrocarbons. Doing a free radical substitution reaction, the bromine-bromine bond is broken through homolytic cleavage. Homolytic cleavage is defined as shared electrons being given to each atom. The mechanism of the bromination of arenes is composed of the initiation, propagation, and termination steps. During the initiation step, the bromine-bromine bond is broken forming bromine radicals in the presence of light. In the next step, propagation, the bromine radical attacks a hydrogen from a carbon-hydrogen bond forming a carbon radical and a haloalkane. The electrophilic carbon then attacks the other bromine radical to produce the product and a…show more content…
The predicted order was wrong because the ordered was based on the stability of the aromatic rings and steric hindrance. With that notion in mind, cyclohexane was predicted to have the fastest relative rate due to not having pi bonds, making it nonaromatic, and because of the hydrogen substituents, not having steric hindrance. On the contrary, cyclohexane was one not one of the first to react because aromatic rings increase the stability of benzene rings and benzylic hydrogens are more reactive than the aliphatic hydrogens on cyclohexane. The next hydrocarbon expected to have a faster relative rate was methyl cyclohexane. Methyl cyclohexane similar to cyclohexane is nonaromatic but due to the methyl group as a substituent, methyl cyclohexane was expected to be less reactive than cyclohexane. The opposite happened where methyl cyclohexane reacts before cyclohexane. The reason being that methyl cyclohexane has a 3˚ aliphatic hydrogen while cyclohexane only has a 2˚ aliphatic hydrogen. Toluene was predicted next because it was the only aromatic ring with the least amount of substituents. Toluene actually had the second fastest reaction rate due to having 1˚ benzylic hydrogens. Benzylic hydrogens tend to react first and quickly. Tert-butylbenzene was then predicted to be next because it seemed to have more stability than ethyl benzene since it has more substituents. In actuality, the reaction rate of tert-butylbenzene reaction was slower than ethylbenzene and ended up being the last hydrocarbon to react because it only has a 1˚ aliphatic and aromatic hydrogens. The predictions made were on the basis of bulkier substituents would increase steric hindrance making the hydrocarbon less reactive. Ethylbenzene has a 2˚ benzylic hydrogen which reacted first in light. In
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