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Alpha and beta carbon
The alpha carbon (α carbon) in organic molecules refers to the first carbon atom that attaches to a functional group, such as a carbonyl. The second carbon atom is called the beta carbon, and the system continues naming in alphabetical order with Greek letters.
The nomenclature can also be applied to the hydrogen atoms attached to the carbons. A hydrogen attached to an alpha carbon is called an alpha-hydrogen, a hydrogen on the beta-carbon is a beta hydrogen, and so on.
This naming standard may not be in compliance with IUPAC nomenclature, which encourages that carbons be identified by number, not by Greek letter, but it nonetheless remains very popular, in particular because it is useful in identifying the relative location of carbons to other functional groups.
Organic molecules with more than one functional group can be a source of confusion. Generally the functional group responsible for the name or type of the molecule is the "reference" group for purposes of carbon naming. For example, the molecules nitrostyrene and phenethylamine are very similar; the former can even be reduced into the latter. However, nitrostyrene's α-carbon is adjacent to the styrene group; in phenethylamine this same carbon is the β-carbon, as phenethylamine (being an amine rather than a styrene) counts its atoms from the opposite "end" of the molecule.
==Examples==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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