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The IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created. For ordinary communication, to spare a tedious description, the official IUPAC naming recommendations are not always followed in practice, except when it is necessary to give an unambiguous and absolute definition to a compound, or when the IUPAC name is simpler (e.g. ethanol instead of ethyl alcohol). Otherwise the common or trivial name may be used, often derived from the source of the compound (see below). In addition, very long names may be less concise than structural formulae. ==Basic principles== In chemistry, a number of prefixes, suffixes and infixes are used to describe the type and position of functional groups in the compound. The steps for naming an organic compound are: # Identification of the parent hydrocarbon chain. This chain must obey the following rules, in order of precedence: ##It should have the maximum number of substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, the one with highest precedence should be used. ##It should have the maximum number of multiple bonds ##It should have the maximum number of single bonds. ##It should have the maximum length. # Identification of the parent functional group, if any, with the highest order of precedence. # Identification of the side-chains. ''Side chains are the carbon chains that are not in the parent chain, but are branched off from it.'' # Identification of the remaining functional groups, if any, and naming them by their ionic prefixes (such as hydroxy for -OH, oxy for =O, oxyalkane for O-R, etc.). Different side-chains and functional groups will be grouped together in alphabetical order. (The prefixes di-, tri-, etc. are not taken into consideration for grouping alphabetically. For example, ethyl comes before dihydroxy or dimethyl, as the "e" in "ethyl" precedes the "h" in "dihydroxy" and the "m" in "dimethyl" alphabetically. The "di" is not considered in either case). When both side chains and secondary functional groups are present, they should be written mixed together in one group rather than in two separate groups. # Identification of double/triple bonds. # Numbering of the chain. This is done by first numbering the chain in both directions (left to right and right to left), and then choosing the numbering which follows these rules, in order of precedence ##Has the lowest-numbered locant (or locants) for the suffix functional group. Locants are the numbers on the carbons to which the substituent is directly attached. ##Has the lowest-numbered locants for multiple bonds (The locant of a multiple bond is the number of the adjacent carbon with a lower number). ##Has the lowest-numbered locants for prefixes. #Numbering of the various substituents and bonds with their locants. If there is more than one of the same type of substituent/double bond, a prefix is added showing how many there are ( di - 2 tri - 3 tetra - 4 then as for the number of carbons below with 'a' added) The numbers for that type of side chain will be grouped in ascending order and written before the name of the side-chain. If there are two side-chains with the same alpha carbon, the number will be written twice. Example: 2,2,3-trimethyl- . If there are both double bonds and triple bonds, "en" (double bond) is written before "yne" (triple bond). When the main functional group is a terminal functional group (A group which can only exist at the end of a chain, like formyl and carboxyl groups), there is no need to number it. # Arrangement in this form: Group of side chains and secondary functional groups with numbers made in step 3 + prefix of parent hydrocarbon chain (eth, meth) + double/triple bonds with numbers (or "ane") + primary functional group suffix with numbers. Wherever it says "with numbers", it is understood that between the word and the numbers, the prefix(di-, tri-) is used. # Adding of punctuation: ## Commas are put between numbers (2 5 5 becomes 2,5,5) ## Hyphens are put between a number and a letter (2 5 5 trimethylheptane becomes 2,5,5-trimethylheptane) ## Successive words are merged into one word (trimethyl heptane becomes trimethylheptane) Note: IUPAC uses one-word names throughout. This is why all parts are connected. The finalized name should look like this: #,#-di''<side chain>''-#-''<secondary functional group>''-#-''<side chain>''-#,#,#-tri''<secondary functional group><parent chain prefix><If all bonds are single bonds, use "ane">''-#,#-di''<double bonds>''-#-''<triple bonds>''-#-''<primary functional group>'' Note: # is used for a number. The group secondary functional groups and side chains may not look the same as shown here, as the side chains and secondary functional groups are arranged alphabetically. The di- and tri- have been used just to show their usage. (di- after #,#, tri- after #,#,#, etc.) Example: Here is a sample molecule with the parent carbons numbered: center For simplicity, here is an image of the same molecule, where the hydrogens in the parent chain are removed and the carbons are shown by their numbers: center Now, following the above steps: # The parent hydrocarbon chain has 23 carbons. It is called tricosa-. # The functional groups with the highest precedence are the two ketone groups. ## The groups are on carbon atoms 3 and 9. As there are two, we write 3,9-dione. ## The numbering of the molecule is based on the ketone groups. When numbering from left to right, the ketone groups are numbered 3 and 9. When numbering from right to left, the ketone groups are numbered 15 and 21. 3 is less than 15, therefore the ketones are numbered 3 and 9. The smaller number is always used, not the sum of the constituents numbers. # The side chains are: an ethyl- at carbon 4, an ethyl- at carbon 8, and a butyl- at carbon 12. Note:The -O-CH3 at carbon atom 15 is not a side chain, but it is a methoxy functional group # * There are two ethyl- groups. They are combined to create, 4,8-diethyl. # * The side chains are grouped like this: 12-butyl-4,8-diethyl. (But this is not the final grouping, as functional groups may be added in between.) # The secondary functional groups are: a hydroxy- at carbon 5, a chloro- at carbon 11, a methoxy- at carbon 15, and a bromo- at carbon 18. Grouped with the side chains, this gives 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxy # There are two double bonds: one between carbons 6 and 7, and one between carbons 13 and 14. They would be called "6,13-diene", but the presence of alkynes switches it to 6,13-dien. There is one triple bond between carbon atoms 19 and 20. It will be called 19-yne #The arrangement (with punctuation) is: 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricosa-6,13-dien-19-yne-3,9-dione #Finally, due to Cis-trans isomerism, we have to specify the relative orientation of functional groups around each double bond. For this example, we have (6''E'',13''E'') The final name is (6''E'',13''E'')-18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricosa-6,13-dien-19-yne-3,9-dione. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IUPAC nomenclature of organic chemistry」の詳細全文を読む スポンサード リンク
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