Chirality (optical activity) of lactic acid molecule Mutual image (mirror images). Asymmetric carbon (atomic carbon) and four different atoms or atoms Group The asymmetric carbon is the chiral centers. When there are n Symmetrical center At most 2 n Stereoisomerism Things. If sp three The four groups connected to carbon are different, so these four groups space There are two different ways to arrange: (Figure)
The material with such structure can make polarized light The polarization plane of optical rotation These two structures are called optical isomers. At the same time, these two structures happen to be material object The relationship with mirror image, such as the left and right hands of the same person, is also called Enantiomer or Chiral isomer 。 This phenomenon is called Enantiomerism , this center carbon atom be called Chiral carbon , denoted by * C. In 1849, chemist louis pasteur (Louis Pasteur) found that tartaric acid Salt can deflect the plane aurora Rotate, but use the Tartrate This property cannot be determined. The difference between the two is whether the plane polarized light can rotate. The reason is that the two are Optical isomerism Things. In 1874, Van Hoff and Lebel （ Joseph Le Bel ）Successfully connected to with carbon atom Of tetrahedron Structural theoretical explanation Of this isomer type optical rotation Quality. cause Optical rotation There are two reasons for isomerism: the molecule contains one or more chirality atom 。 1: Contains a Chiral carbon atom There are two Optical rotation Isomers, which have mutual material object and image Is also called Enantiomer 。 Enantiomer It has the same optical rotation ability, but the direction of rotation is opposite chemical property Very similar. 2: Contains two identical attributes carbon atom There are three optically active isomers. 3: When there are several different chiralities in the molecule Atomic time , the number of optical isomers is 2 n , n is the number of different chiral atoms. First Chiral molecule , such as 2-Chlorobutane No. 2 is carbon SP3 hybrid , so it is space tetrahedron The structure is connected with four different Group , respectively H - CH three - CH three CH two -Cl - So this molecule has two structures (I'm sorry I don't have a picture, I can try to draw which two are). If you compare them together, you will find that these two structures are like the real image and Virtual image , which is called chiral molecule. Chiral molecules can rotate the polarization at a certain angle, so this pair Isomer Optical isomer! Most optical isomers have Chiral carbon One carbon is connected to four different molecules Group It must be chiral carbon, that is, optical isomer, on the contrary, it must not be chiral carbon. It should be noted that some Complex There are similar situations, such as CaEDTA. Enantiomer Of Optical rotation The direction is exactly opposite, so it will have different optical rotation Of Main isomer It is called optical isomer. The two substances with equal amount of each other as optical isomers are evenly mixed, and the optical rotations cancel each other to form Racemate 。 For racemate, it can be separated by [1] To separate. 
