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| Shared Idea |
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| Nomenclature of Organic Rings
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| Organic Rings
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| I previously mentioned the use of the prefix "cyclo" when naming hydrocarbons that have a chain of carbon atoms joined in a ring. More complicated organic rings also exist, and some were named before the actual structure was known, meaning that alternative names exist for the same compound. Many of these compounds appear in organic chemistry, biology and industry and are therefore worth understanding.
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| A central compound among this group of chemicals is benzene. The formula of benzene is C6H6. It consists of a ring of six carbon atoms joined in a ring of alternating single and double bonds. In 1865, Friedrich August Kekule published a paper describing this structure. He explained that he had dreamt of a snake eating its tail. Each carbon atom also has a single hydrogen atom and the twelve atoms exist in a flat plane structure. However, the crystal structure shows that the molecule is symmetrical, with bonds between the carbon atoms that are shorter than a single carbon-carbon bond yet longer than a double carbon-carbon bond. This leads to several alternate ways of representing a benzene ring, but benzene has remained as the IUAPC name for this compound.
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| Toluene is a highly toxic organic compound that is commonly used as a solvent. It consists of a single carbon atom with three hydrogen atoms (that is, a methyl group) joined to a benzene ring. The IUAPC name for this molecule is methylbenzene, though several alternate names also exist, such as phenylmethane. This is because the prefix "phenyl" refers to a benzene ring joined to a molecule.
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| Xylene has a broad use in industry, as a solvent, thinner or degreasing agent. It has a sweet odor and is also used in forming plastics. Xylene has two methyl groups joined to a benzene ring and is named dimethylbenzene, but that is not sufficient. Three isomers exist, depending on how the methyl groups are situated. The prefixes ortho, meta and para are used to discern the geometry. "Ortho" refers to the methyl groups being attached to neighboring carbon atoms (numbers 1 and 2). Therefore, ortho-xylene is 1,2-dimethylbenzene. Similarly, meta-xylene is 1,3-dimethylbenzene and para-xylene is 1,4-dimethylbenzene. Following a previously noted nomenclature rule, the numbering of the carbon atoms in the ring start with one branch and then numbering so as to have the smallest possible numbers used in the name.
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| Phenol, also known as carbolic acid, is used to make plastics, medicines and other products. It has a hydroxyl group replacing a hydrogen atom in a benzene ring. The chemical formula is C6H5OH and the IUPAC name is benzenol.
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| Another interesting set of organic rings are purines and pyrimidines. In addition to having carbon, hydrogen and oxygen atoms, they also include nitrogen atoms. These are the central components of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Purines (adenine and guanine) each have a double ring, making them longer. Pyrimidines (thymine, cytosine and uracil) have a single ring. In both DNA and RNA, a purine pairs with a pyrimidine, storing the genetic information. In RNA, uracil replaces thymine.
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