How to name organic compounds?
The systematic nomenclature of alkanes can be divided into straight chain and branched chain.
1. Linear alkane:
The naming of straight-chain alkanes is the same as customary law, except that the orthography in "normal alkanes" is removed and directly called "normal alkanes". Example:
CH3CH2CH2CH2CH3
It is called n-pentane in common law.
It is called n-pentane in the system method.
2. Naming principles of branched alkanes:
(1). Select the main chain.
The chain with the largest number of carbon atoms is selected as the main chain, and it is named as "an alkane" according to the carbon number (straight chain) of the main chain. Example:
The longest C chain has four C atoms, which is called "butane", and the remaining methyl groups are used as substituents.
2- methylbutane
If two or more longest carbon chains (with the same number of C) can be selected, the carbon chain with the most substituents should be the main chain. Example:
The longest carbon chain contains six C's, three of which can be selected, and the substitution bases are 2, 3 and 4 respectively. The main chain should be selected on the carbon chain with the most substituents.
2,5-dimethyl-3,4-diethylhexane
(2). Main chain carbon number
Numbering principle: minimum series principle-that is, the main chain carbon is numbered from the end closest to the substituent.
After numbering, determine the position of each substituent. Numbers are written before the substituent names, separated by short crosses, and then written before the main chain names to form a complete name.
In order to indicate the position of substituents, the main chain carbon should be numbered with Arabic numerals.
Example:
2,7,8-trimethyldecane (not 3,4,9-trimethyldecane)
(3) When there are multiple substituents on the main chain, the number should be based on the principle of minimum series, and the number of similar substituents should be indicated in Chinese, such as "two, three, four ……", and the order of substituents should be separated by commas. For example:
When it is impossible to judge whether the substituent is the lowest series from left to right, it depends on the position of other substituents and still follows the principle of the lowest series. The correct name is 2,4,8-trimethyl nonane, as shown in the above example.
(4) When different alkyl groups are attached to the main chain.
Simple alkyl groups are written at the front, and complex alkyl groups are written at the back, such as:
3- ethyl -4- methylheptane
Order of alkyl size:
(See cis-trans isomerization of olefins for details).
Note that the size of alkyl groups is arranged in alphabetical order when naming in English.
(5) If alkyl groups with different sizes are in the same position from both ends,
Then the smaller group should have a smaller rank.
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1. Select the main chain (the longest carbon chain)
2. Main chain number (principle 1. Minimum series. 2. The smaller the group, the smaller the order)
3. Write down the name (first small, then big)
Author: Lecturer A replied to this speech on 2006- 12-22 13:32.
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4 Reply: Naming method of organic compounds
According to IUPAC nomenclature and chinese chemical society nomenclature principle 1980, the compounds are described as follows.
1. Branched alkanes
The main chain is the longest carbon chain with the most branches.
Number according to the lowest series of rules. Number from the nearest end of the * side chain. If the numbers at both ends are the same, the next substituent is compared in turn, and the lowest system is the one that satisfies the minimum first (regardless of the nature of the substituent). For example,
It is named 2,3,5-trimethylhexane instead of 2,4,5-trimethylhexane because 2,3,5 is the lowest series compared with 2,4,5.
IUPAC stipulates that the order of substituents is arranged in alphabetical order of English names. Our country adopts the "order rule" in stereochemistry: the priority group is put behind, and if the first atom is the same, the next atom is compared. For example,
It's called 2- methyl -3- ethylpentane, because -ch2ch3 >-CH3, so -CH3 comes first.
2. Monofunctional compounds
The main chain is the longest carbon chain with functional groups, and it is also the carbon chain with the most side chains, which is called olefins (or alkynes, alcohols, aldehydes, ketones, acids, esters, ...). Halogenated hydrocarbons, nitro compounds and ethers are based on hydrocarbons, with halogen, nitro and alkoxy as substituents, and the positions of substituents are indicated.
The numbering starts from the end of the functional group (or the above substituent) near *, and the priority groups are listed in turn. For example,
3. Multifunctional compounds
(1) fat
Choose the longest carbon chain with the most functional groups (including heavy bonds as far as possible) as the main chain. The suffixes of functional groups are usually indicated in the following order,
—OH>—NH2(=NH)>C≡C>C=C
If the olefin and alkyne are in the same grade, give the number with the lowest double bond. For example,
(2) cycloaliphatic and aromatic
If the side chain is simple, choose the ring as the matrix; If the substituents are complex, the carbon chain is the main chain. For example:
(3) Heterocycles
Numbers from heteroatoms. If there are many heteroatoms, number them in the order of O, S, N and P ... For example:
4. cis-trans isomers
(1) cis-trans nomenclature
Cyclic compounds are represented by cis and trans. The same or similar atoms or genes on the same side are called cis, and those on the other side are called trans. For example,
(2)Z, E nomenclature
When the compound contains a double bond, it is represented by Z and E. According to the "order rule", the size of the groups connected by the double bond atoms is compared. The larger group on the same side is called Z, and the one on the opposite side is called E. ..
The sorting rule is:
(I) the number of atoms is large, such as I > br > cl > s > p > f > o > n > c > h, and the unshared electron pair is the smallest;
(ii) high isotope mass is preferred, for example, d > h；;
(iii) When the first atom in the two groups is the same, the second and third atoms are compared in turn;
(4) Heavy key
Can be regarded as
(Ⅴ) Z takes precedence over E and R takes precedence over S. ..
take for example
(E)- benzaldehyde oxime
5. Optical isomers
(1)D, l configuration
It is mainly used in sugar and related compounds. The sugar with glyceraldehyde as the standard, D-handed configuration and L-handed configuration, and the configuration of chiral carbon atom farthest from carbonyl group in the molecule is the same as D-(+)- glyceraldehyde is called D-type; On the contrary, it is L-shaped. For example,
Amino acids are also labeled with D and L. Except glycine has no optical activity, the carbon atoms of α -amino acids are all L-shaped.
The remaining compounds can be determined by chemical transformation and contact with reference materials. For example:
(2)R, s configuration
When naming the compound Cabcd containing chiral carbon atoms, the four atoms or groups connecting chiral carbon atoms are arranged from big to small according to the "sequence rule" (such as A > B > C > D), and then the smallest D is placed far away from the observer, and the other three groups point to the observer, so that a→b→c is R clockwise and S counterclockwise; If d points to the observer, it is s clockwise and r counterclockwise. In practical use, the most commonly used expression is Fisher projection, such as:
It is called (R)-2- chlorobutane. Because Cl > C2H5 > CH3 > H, and the smallest group H is above and below the C atom (meaning backward), which is far away from the observer, the nomenclature stipulates that Cl→C2H5→CH3 is R clockwise. Another example is that,
Named (2R, 3r)-(+)- tartaric acid, because
The H of C2 is around the C atom (meaning forward), which points in the direction of the observer, so it is stipulated by the nomenclature, although
Seen counterclockwise, C2 is r. C3, and C2 is similar.