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Diastereomers (sometimes called diastereoisomers) are a type of a stereoisomer.〔IUPAC "Gold Book" (''diastereoisomerism'' ) 〕 Diastereomerism occurs when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and are not mirror images of each other.〔.〕 When two diastereoisomers differ from each other at only one stereocenter they are epimers. Each stereocenter gives rise to two different configurations and thus increases the number of stereoisomers by a factor of two. Diastereomers differ from enantiomers in that the latter are pairs of stereoisomers that differ in all stereocenters and are therefore mirror images of one another.〔IUPAC "Gold Book" (''enantiomer'' ) 〕 Enantiomers of a compound with more than one stereocenter are also diastereomers of the other stereoisomers of that compound that are not their mirror image. Diastereomers have different physical properties (unlike enantiomers) and different chemical reactivity. Diastereoselectivity is the preference for the formation of one or more than one diastereomer over the other in an organic reaction. ==Syn / anti== When the single bond between the two centres is free to rotate, cis/trans descriptors are invalid. Two widely accepted prefixes used to distinguish diastereomers on sp³-hybridised bonds in an open-chain molecule are syn and anti. Masamune proposed the descriptors which work even if the groups are not on adjacent carbons. It also works regardless of CIP priorities. Syn describes groups on the same face while anti describes groups on opposite faces. The concept applies only to the Zigzag projection. The descriptors only describe relative stereochemistry rather than absolute stereochemistry. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「diastereomer」の詳細全文を読む スポンサード リンク
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