Substituent Order Rules For Organic Chemicals

In order to have a reasonable and simple expression of the stereochemical relations of asymmetric compounds in organic chemistry, R.S. Ingold, R.C. Kane, V. Prelug and others proposed to arrange the substituent groups by atomic number, with the highest atomic number at the front and the lowest atomic number at the back. The method is called priority rule of atoms or groups of atoms, or order rule or order rule. In determining the priority of atoms or groups, certain provisions have been formulated, the main contents of which are as follows:
The various substituent atoms are arranged according to their atomic number size, the larger is the "better" group, and if it is an isotope, the higher quality is the "better" group. E.g. Cl>O>C>H; D>H, > indicates superior.
If the first element of two groups is the same (e.g. C), compare the atoms directly connected to it. In order of atomic number, the largest of each group is compared first, and if it is still the same, then the second and third are compared successively. For example Cl, H, H>O, O, C; Cl, O, H>Cl, C, C, if still the same, are compared successively along the substitution chain.
(3) Groups containing double and triple bonds are treated as two or three single bonds, and can be considered to have two or three identical atoms.
By mastering the order rules of substituents, we can not only correctly express the Z.E name in geometric isomers, but also correctly judge the configuration R.S of optical isomers. In the naming of compounds, the atoms or groups of atoms that act as substituents in the same compound should be arranged in a regular order, with the more advantageous groups in the back