Optical isomerism

Isomerism is a type of stereoisomerism that has the same general chemical properties but differs only in optical rotation. It is a type of stereoisomerism. Generally, optically active substances, such as lactic acid, exist in a pair of isomers, the dextrorotatory D -isomer and the levorotatory L -isomer. Their stereochemical structures are in a mirror image relationship, and are represented by a pair of figures called antipodes (enantiomers). Figure (A) and (B) are in a mirror image relationship, and cannot be superimposed on each other, so they represent different substances. In this case, the central carbon atom is surrounded by different atoms or groups a, b, c, and d, making it an asymmetric carbon atom. In this way, a compound of the C _abcd type, which has one asymmetric carbon atom at the center of the molecule, has a pair of enantiomers and their racemic compounds. However, when there are two asymmetric carbon atoms, four types of isomers are produced as compounds of the C _abc -C _a′b′c′ type, resulting in two pairs of enantiomers and two racemic compounds. In this case, a compound with a symmetrical chemical structure, C _abc -C _abc , will produce a pair of enantiomers, one racemic compound, and one meso compound that has lost its optical rotation.
(1) In addition to those with asymmetric carbon atoms,
(2) Those in which the asymmetric carbon atom is part of a ring structure (e.g., terpenes, alkaloids),
(3) Molecular asymmetry,
(4) Compounds in which atoms such as N, S, Se, Sn, Si, and P contained in the compound as tetravalent atoms are asymmetric atoms, and
(5) Complexes in which the asymmetric atom is a metal,
It can be seen in.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

通常の化学的性質が同じで，旋光性のみを異にする異性．立体異性の一つ．一般に旋光性の物質には，たとえば乳酸のように，右旋性のD-体と左旋性のL-体の一対の異性体が存在する．その立体化学構造は，実体と鏡像の関係にあり，互いに対掌体(鏡像異性体)といわれる一対の図形によって表される．図の(A)と(B)とは互いに実体と鏡像の関係にあって，重ね合わすことができないから異なる物質を表している．この場合，中心の炭素原子はa，b，c，dの相互に異なる原子または基で囲まれており，不斉炭素原子である．このように1個の不斉炭素原子を分子の中心に有する C_abcd 形の化合物には，一対の対掌体とそのラセミ化合物とがある．しかし，2個の不斉炭素原子がある場合には，C_abc-C_a′b′c′ 形の化合物として4種類の異性体ができるから，二対の対掌体と2個のラセミ化合物ができる．この場合，化学構造が対称的な C_abc-C_abc 形の化合物では，一対の対掌体と1個のラセミ化合物，それに旋光性を失った1個のメソ化合物ができる．光学異性を示す物質は，上記のように，
(1)不斉炭素原子をもつもののほかに，
(2)不斉炭素原子が環構造の一部をなすもの(例：テルペン類，アルカロイド類)，
(3)分子不斉によるもの，
(4)四価として化合物中に含まれるN，S，Se，Sn，Si，Pなどの原子が不斉原子となっている化合物，および，
(5)不斉原子が金属である場合の錯体，
にみられる．

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