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In IUPAC nomenclature, a number of prefixes, suffixes and infixes are used to describe the type and position of functional groups in the compound.
Straight-chain alkanes take the suffix "-ane" and are prefixed depending on the number of carbon atoms in the chain, as given by the following table:
| Number of carbons | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Prefix | Meth | Eth | Prop | But | Pent | Hex | Hept | Oct | Non | Dec | Undec | Dodec |
For example, the simplest alkane is CH4 methane, and the nine-carbon alkane CH3(CH2)7CH3 is named nonane.
Cyclic alkanes are simply prefixed with "cyclo-", for example C4H8 is cyclobutane and C6H12 is cyclohexane.
Branched alkanes are named as a straight-chain alkane with attached alkyl groups. They are prefixed with a number indicating the carbon the group is attached to, counting from the end of the alkane chain. Infixed is the name of the substituant, as for alkanes in the table above, plus "-yl". For example, (CH3)2CHCH3, commonly known as isobutane, is treated as a propane chain with a methyl group bonded to the middle (2) carbon, and given the systematic name 2-methylpropane. Numbers may be dropped when there is no ambiguity, so 2-methylpropane is just methylpropane. (1-methylpropane would be identical to butane).
If there is ambiguity in the position of the substituant, depending on which end of the alkane chain is counted as "1", then numbering is chosen so that the smallest number is used. For example, (CH3)2CHCH2CH3 (isopentane) is named 2-methylbutane, not 3-methylbutane. Since this resolves the ambiguity, the number is again dropped in this case.
If there are multiple side-branches of the same size alkyl group, their positions are separated by commas and the group prefixed with di-, tri-, tetra-, etc., depending on the number of branches (e.g. C(CH3)4 2,2-dimethylpropane). If there are different groups, they are added in alphabetical order, separated by commas or hypens: 3-ethyl-4-methylhexane. The longest possible main alkane chain is used; therefore 3-ethyl-4-methylhexane instead of 2,3-diethylpentane, even though these describe equivalent structures. The di-, tri- etc. prefixes are ignored for the purpose of alphabetical ordering of side chains. (eg 3-ethyl-2,4-dimethylpentane, not 2,4-dimethyl-3-ethylpentane)
Subsidiary branches off a side-chain are prefixed according to a secondary numbering system specific to that side branch, numbering from the point of attachment to the main chain, and then the whole side-branch is parenthesised and treated as a single substituent. For example, 4-(1-methylpropyl)octane is a octane chain with a side chain bonded to the 4th carbon, the side chain consisting of a propyl group with a methyl group attached to the carbon closest to the main chain.
Alkenes are named for their parent alkane chain with the suffix "-ene" and an infixed number indicating the position of the double-bonded carbon in the chain: CH2=CHCH2CH3 is but-1-ene. Ethene ( ethyleneProperties General Name Ethene Chemical formula C H C H Formula weight 28. 05 amu Synonyms Ethylene, Olefiant gas CAS number 74-85-1 UN number 1038 Phase behavior Melting point 104 K (-169. 1 °C) Boiling point 169. 7°C) Thermal decomposition ? K (?°C) Tri) and propene do not require infixed numbers, since there is no ambiguity in the structures. As before, the lowest number is used.
Multiple double bonds take the form -diene, -triene, etc., with the size prefix of the chain taking an extra "a": CH2=CHCH=CH2 is buta-1,3-diene. Simple cisThis article is about uses of the word "cis"; for the abbreviation "CIS" see CIS. Cis is a Latin word meaning "on the same side" and is the opposite of trans''. Its uses include: In chemistry, a double bond in which the greater radical on both ends is on and transIn chemistry, a double bond in which the greater radical on both ends is on the opposite side of the bond is called trans . Compare with cis''. In the diagram on the right, the hydrogen atoms are on opposite sides of the double bond. They cannot rotate to isomersIn chemistry, geometric isomerism is a form of stereoisomerism and describes the orientation of functional groups at the ends of a bond around which no rotation is possible. Such bonds are typically double bonds, but they can also be part of a ring struct are indicated with a prefixed cis- or trans-: cis-but-2-ene, trans-but-2-ene. More complex geometric isomerisations are described using the Cahn Ingold Prelog priority rulesFor compounds found in organic chemistry, the Cahn Ingold Prelog priority rules are used to determine the orientation of a molecule for purposes of assigning stereochemistry at a stereocenter and for assigning the name of isomers of molecules possessing d.
Alkynes are named using the same system, with the suffix "-yne" indicating a triple bond: ethyne ( acetyleneThe chemical compound acetylene also called ethyne was discovered in 1836 by Edmund Davy, in England; its chemical formula is C H and its structure is: Acetylene is a colorless and extremely flammable gas at standard temperature and pressure with a garlic), propyne ( methylacetyleneMethylacetylene propyne is an alkyne with the chemical formula H C≡ C H. It is a component of MAPP gas, which is commonly used in gas welding.).