Carcinogenic Hydrocarbons

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Are Aromatic Hydrocarbons Carcinogenic
Aromatic hydrocarbons or arenes are hydrocarbons characterized by alternating double and single bonds between carbons. Benzene is the most common aromatic hydrocarbon, but there are some non-benzene based compounds called heteroarenes, where a carbon is replaced by an oxygen, nitrogen, or sulfur, that are also aromatic compounds.

Aromatic hydrocarbons exist in our daily lives regardless if we recognize them or not. Aromatic hydrocarbons are ingested or inhaled in our body by way of drugs, cigarette smoke, and automobile exhaust. Once in the body, they are converted into arene oxides by cytochrome P₄₅₀. An arene oxide is a compound in which one of the double bonds of the aromatic ring has been converted into an epoxide. The changing of the aromatic hydrocarbon into an epoxide forms a more water-soluble compound that can be eliminated from the body.

Arene oxides can react in two ways. They can undergo attack by a nucleophile to form addition products or rearrange to form a phenol.

Some aromatic hydrocarbons are carcinogens, meaning they can cause cancer. Investigations have shown that hydrocarbons themselves are not carcinogenic, but the carcinogens are the oxidation products of the aromatic molecules. Nucleophiles react with epoxides to form addition products. 2’-Deoxyguanosine, a component of DNA, has a nucleophilic NH₂ group that is known to react with certain arene oxides. Once it attaches to an arene oxide, the 2’-deoxyguanosine can no longer fit into the DNA. This results in the genetic code not being properly transcribed, which can lead to mutations that cause cancer.

Arene oxides’ becoming carcinogenic depends on the rates of its two reaction pathways: rearrangement and reaction with a nucleophile. When an arene oxide rearranges, it forms phenols which are not carcinogenic. However, the formation of two addition products from nucleophilic attack by DNA can be carcinogenic. If the rate of arene oxide...
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