Order rules:
1． What is an order rule? The order rule is the rule that the various substituents are prioritized.
2． What are the main contents of the order rules?
(1) Atoms: The number of atoms with large numbers is in the front, and the number of isotopes with large mass is preferred. The priority of several common atoms is: i>br>cl>s>p>o>n>c>h
(2) Saturated group: If the number of the first atom is the same, the atomic number of the second atom is compared, and so on. Common hydrocarbon group priorities are: (ch3)3c->(ch3)2ch->ch3ch2->ch3-
(3) Unsaturated groups: can be seen as connected to two or three identical atoms. The priority of unsaturated hydrocarbon groups is: -cch>-ch=ch2>(ch3)2ch-
3． Where are the order rules mainly applied?
(1) When the cis- and transverse isomers of olefins are named, when the four groups on the double-bonded carbon atoms are not even the same, they cannot be expressed by cis-trans, but can only be expressed by z and e. Comparing the priority of the two pairs of groups according to the "order rule", the preferred groups on the same side of the double bond carbon atom are z-type, and vice versa, they are e-type. For example:
c=c
According to the "order rule", the priority order of the two pairs of groups connected by the double bond carbon atoms is compared, -ch3 >-h, -ch2ch2ch3 >-ch2ch3, and the two preferred groups are on the same side of the double bond carbon atom, so it is z-type.
The longest carbon chain containing double bonds in the structural formula is selected as the main chain, and the main chain in the above formula is 6 carbon atoms, called hexene.
The main chain carbon atoms are numbered, starting with Arabic numerals at the end closest to the double bond, to determine the position of the double bond and the substituent. The above equation starts from the left to number, the double bond carbon atom is in 2 bits, and the ethyl group is in 3 bits.
Write the name, placing the configuration, substituent name before the parent name, the substituent bit before the substituent name, and the double key bit before the parent name, separated by a half-word line "-".
The above compound is named (z)-3-ethyl-2-hexene.
(2) Enantiomers are represented by a Fischer projection, and the configuration of the chiral carbon atoms should be represented when naming. The configuration of the enantiomer has d, l and r, s two labeling methods, d, l labeling method to glyceraldehyde as the standard, there are certain limitations, some compounds are difficult to determine its correspondence with the structure of glyceraldehyde, therefore, more is the application of r, s labeling, it is based on the chiral carbon atoms connected by four different atoms or groups in the order of arrangement in space labeling. For example:
According to the projection type to judge the configuration, first of all, it should be clear that in the projection type, the groups connected by the horizontal line are forward, and the groups connected by the vertical line are backward; and then the priority order of the four groups connected by the chiral carbon atoms is arranged according to the "order rules" in the above formula: -oh>-cooh>-ch2-ch3>-h; the smallest group hydrogen atom is the top of the regular tetrahedron centered on the carbon atom, and the remaining three groups are the corner top of the triangle at the bottom of the tetrahedron, and the three groups are viewed from the bottom of the tetrahedron to the top direction. Or, stand opposite the smallest atom and observe the order of the remaining three groups, starting with the optimal group, clockwise r and counterclockwise s. In the above formula, from -oh -cooh -ch2-ch3 is clockwise, so the compound represented by the projection formula is the r configuration, named: (r)-2-hydroxybutyric acid.
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