aromatic hydrocarbons

Aromatic hydrocarbons are hydrocarbons with a single bond or a double bond, and between carbon atoms. Configuration 6 carbon atoms in an aromatic compound called benzene rings. Aromatic hydrocarbons can be monocyclic or polycyclic. Some aromatic compounds that are not called heteroarena benzene derivatives, these compounds follow Hückel Rule.In organic chemistry, Hückel rule determines a planar ring molecules have aromatic properties. This rule was proposed by the German chemist Erich Hückel in 1931.

A planar ring molecules meet Hückel rule, if it has as many as π electron-4N +2, where n is an integer.

From the data aromatics hydrogenation of alkenes are more stable than expected, the stability of the "extra" is caused by a cloud of delocalized electrons, called resonance energy. Criteria for simple aromatic compounds:

    1. Meet Hückel rule, have much 4N π electron cloud +2 in the delocalized p-orbital.
    2. Shaped planar and cyclic.
    3. Each atom in the ring must be able to participate in the delocalization of electrons by having a p-orbital or lone pair.
In these aromatic compounds, at least one carbon atom is replaced by another atom, such as oxygen, nitrogen, or sulfur. One example is the compound furan, a heterocyclic ring compound having 5 members, one oxygen atom. Another example is pyridine, a heterocyclic ring compound with 6 members, one nitrogen atom. 

aromatic substitution 
In aromatic substitution, 1 substituents on the ring arena (usually hydrogen) will be replaced with other substituents. 2 main types are electrophilic aromatic substitution (active electrophile reagent) and nucleophilic aromatic substitution (reagennya nucleophile). In the radical-nucleophilic aromatic substitution, a radical form of active reagents. One example is the nitration of salicylic acid. 

couplings
At couplings, metal will catalyze the coupling between the two radical fragments formal. The results are usually obtained from the coupling reaction is the formation of new carbon-carbon bonds, for example alkilarena, vinyl arena, biraril, the carbon-nitrogen (aniline) or a carbon-oxygen bond new. An example is the arylation of perfluorobenzena

Polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons are carcinogenic particular one, meaning that there are cancerous. These compounds can produce tumors in mice within a very short time even though only a few are applied to the skin. This is not only carcinogenic hydrocarbons present in coal tar, but also the soot and tobacco smoke and can form in the meat baker. Biological effects have been known for a long time, ie since 1775, when the soot is defined as a cause of cancer of the penis chimney cleaning. Incidence of lip cancer and heart disease are also found in the smoker.

How these carcinogens cause cancer now began to unfold. To eliminate hydrocarbons, mengoksidasinya body to be more soluble in water, making it easier excreted. Metabolic oxidation product appears to be the major cause of cancer. For example, one of the most potent carcinogens of this type is benzo [a] pirena. Enzymatic oxidation converts it into diol-epoxide as shown in the figure below.

Diol-epoxide is then reacted with the cell's DNA, causing mutations that ultimately prevents cells reproduce normally.

Benzene is highly toxic (toxic) to humans and can cause severe liver damage, but toluene, though not dangerous, is much less toxic. How might these two similar compounds behave differently? To eliminate benzene from the body, must be in cinci aromatic oxidation, and this oxidation intermediates of a destructive nature. However, the side chain methyl of toluene can be oxidized to produce benzoic acid, which can be excreted. Intermediates in this process can not cause health problems.

While some chemicals can cause cancer, other substances can change or heal. Many substances that can prevent cancer growth, and assessment of cancer chemotherapy has been widely sumbangnya human health.