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Hydrocarbons are a family of organic compounds that are made up solely of carbon and hydrogen. These compounds include linear, branched, cyclic, and polycyclic alkanes and spirans, as well as alkenes, alkynes, aromatic hydrocarbons, and more.
As they are the compounds with the simplest composition and structure of all organic compounds, hydrocarbons, and in particular linear alkanes, form the basis of all organic nomenclature. In this sense, even the compound with the most complex structure and composition can be considered as a linear or cyclic main chain derived from some alkane, provided with different substituents, functional groups, etc.; therefore, it can be named as such.
Even the same branches can be seen as radicals obtained by the removal of one or more hydrogens from an alkane, which allows it to join the main chain. In short, since both the main chains of all organic compounds and their branches can be related to a linear alkane, then the names of the former can also be related to the names of the latter.
The nomenclature of linear alkanes: a system of prefixes and a suffix
Chemical nomenclature has two main purposes:
- Give a unique and unequivocal name to each organic compound; that is, give different names to all the compounds so that they are not confused.
- Deduce the molecular structure of a chemical compound from its name, a process that in nomenclature is called “formulation”.
In the construction of names in systematic chemical nomenclature (particularly that of the International Union of Pure and Applied Chemistry or IUPAC), names usually consist of two halves: a prefix followed by a suffix. This is precisely the structure of the names of linear alkanes.
The suffix of the alkanes
We will start with the suffix, despite being the final part of every name. The suffix is always used in IUPAC nomenclature to identify the type of compound in question. That is, it represents the general part of the compound name. When dealing with an alkane, the name of the compound ends with the same suffix that the word alkane has, i.e. -ane . This suffix comes from the Latin – anus which indicates origin or belonging.
This means that the names of all the alkanes share the same and unique suffix, or what is the same, they end in the same three letters.
The prefixes of the alkanes
If the suffix identifies the general type of compound, the prefixes, instead, are used to identify the particular compound.
Due to their very simple structure, both naming and formulating linear alkanes is very easy. Linear alkanes consist of saturated hydrocarbons with the general molecular formula C n H 2n+2 . With the exception of methane, which has a single carbon atom surrounded by four hydrogens, the structure of linear alkanes consists of two CH 3 – groups linked by a chain of –CH 2 – groups.
This means that alkanes can be distinguished simply by the number of carbon atoms they have, since their structure can be deduced from that number. Therefore, the nomenclature of linear alkanes only needs to unambiguously identify the number of carbon atoms in the structure, and it does this by means of a set of prefixes.
The prefixes of the first four alkanes
The names of the first four alkanes are among the few names in IUPAC nomenclature that are not derived from the application of a set of systematic rules. Instead, they are names derived from ancient names to which the suffix for the alkanes seen above was added. These are the first four alkanes and the origin of their respective prefixes:
| Alkane | number of carbons | Prefix | Origin of the Prefix |
| Methane | 1 | met- | The prefix met- is used to identify compounds and radicals with a single carbon atom and comes from methanol. This alcohol is obtained from wood, and its name comes from a Greek expression that literally means wood alcohol. |
| ethane | 2 | et- | The prefix et- comes from the word ether, which is how the ethyl ether produced by the condensation of ethanol catalyzed by sulfuric acid was formerly known. |
| Propane | 3 | prop- | This prefix comes from propionic acid (today known as propanoic acid). The name consists of the union of the Greek terms protos and pion that mean first fat. This refers to the fact that it is the smallest carboxylic acid (the first) that is insoluble in water (just like fatty acids). |
| Butane | 4 | but- | The prefix but- also comes from a carboxylic acid, in this case the four-carbon one that was first isolated from butter ( butyrum in Latin). |
The prefixes of the other alkanes
The prefixes of all alkanes and their derivatives having five or more carbon atoms consist of the Greek numeral prefixes and indicate directly how many carbons are in the chain.
These prefixes are, in many cases, of daily use. This is the case of tri- , which is part of the word tricycle or trilogy and penta- or hexa- which are part of pentagon and hexagon and indicate the number of sides of said geometric figures. When used as units, the final a is omitted ( tetr- , pent- , hex- , etc.)
The prefixes for the first two tens are deca- and eicosa- , but for the rest of the tens it is constructed by combining the respective numerical prefix with -conta- (as in triaconta- , tetraconta- , etc.)
Likewise, 100 carbon atoms are identified with the prefix hecta- and the other hundreds are built by combining the first prefixes with -hecta- ( dohecta- , trihecta- , tetrahecta- , etc.).
The following section presents a long list of prefixes ranging from the smallest to the largest. It should be noted that, in the particular case of cyclic alkanes, all the prefixes in the following list must be preceded by the prefix cilco- (for example, cyclopropa- , cyclopenta- , etc.).
List of hydrocarbon prefixes from 1 to 10,000
| number of carbons | Linear Alkane Name | Prefix | number of carbons | Linear Alkane Name | Prefix | |
| 1 | Methane | Met- | 27 | Heptacosane | Heptacos- | |
| 2 | ethane | Et- | 28 | Octacosan | Octacos- | |
| 3 | Propane | Prop- | 29 | Nonacosan | Nonacos- | |
| 4 | Butane | But- | 30 | triacontano | Triacont- | |
| 5 | pentane | Pent- | 31 | henetriacontano | Henetriacont- | |
| 6 | hexane | Hex- | 32 | dotriacontano | Dotriacont- | |
| 7 | heptane | Hept- | 33 | tritriacontane | Tritriacont- | |
| 8 | Octane | Oct- | 3. 4 | Tetratriacontane | Tetratriacont- | |
| 9 | Nonane | No N- | 35 | pentatriacontane | Pentatriacont- | |
| 10 | Dean | Dec- | 36 | hexatriacontano | Hexatriacont- | |
| eleven | undecano | Undec- | 37 | Heptatriacontano | Heptatriacont- | |
| 12 | dodecane | Dodec- | 38 | hexatriacontano | Hexatriacont- | |
| 13 | tridecane | Tridec- | 39 | nonatriacontano | Nonatriacont- | |
| 14 | tetradecane | Tetradec- | 40 | Tetracontane | Tetracont- | |
| fifteen | pentadecane | Pentadec- | fifty | pentacontane | Pentacont- | |
| 16 | hexadecane | hexadec- | 60 | hexacontane | Hexacont- | |
| 17 | heptadecane | Heptadec- | 70 | Heptacontane | Heptacont- | |
| 18 | octadecan | Octadec- | 80 | octacontane | Octacont- | |
| 19 | nonadecane | Nonadec- | 90 | Nonacontano | Nonacont- | |
| twenty | Eicosan | Eicos- | 100 | hectane | Hect- | |
| twenty-one | heneicosan | heneicos- | 150 | Pentacontactane | Pentacontahect- | |
| 22 | Docosan | Docos- | 200 | dihectane | Diject- | |
| 23 | tricosan | Tricos- | 500 | Pentahectane | Pentahect- | |
| 24 | Tetracosan | Tetracos- | 1,000 | kilano | Kil- | |
| 25 | pentacosan | Pentacos- | 5,000 | Pentakilano | Pentakil- | |
| 26 | hexacosane | Hexacos- | 10,000 | miriano | Miri- |
Other hydrocarbon suffixes
As mentioned at the beginning, hydrocarbons are not limited to alkanes, but there are also other types of hydrocarbons such as alkenes, alkynes, and aromatics, to name just a few.
In the case of alkenes and alkynes , which are compounds that have double and triple bonds , respectively, the type of compound is indicated by using the suffixes –ene and –yne instead of –ane. If a compound has several double bonds, then the suffix –ene is preceded by a numeral prefix (equivalent to those in the previous list) and indicating the number of double bonds it contains. For example -diene if it has two double bonds, -tetraene if it has four and so on.
The same can be said for polyfunctional alkynes . Finally, some hydrocarbons contain both double and triple bonds, in which case both suffixes (–ene and –yne) are combined preceded by any relevant numeral prefix.
The use of these suffixes is shown in the following table:
| number of carbons | Number of double bonds | number of triple bonds | Suffix | Name |
| 2 | 1 | 0 | -eno | ethene |
| 2 | 0 | 1 | -ino | ethyno |
| 3 | 1 | 0 | -eno | propene |
| 3 | 0 | 1 | -ino | tipping |
| 4 | 1 | 0 | -eno | butene |
| 4 | 0 | 1 | -ino | Butino |
| 4 | 1 | 1 | -dwarf | butenine |
| 5 | 2 | 0 | -diene | Pentadiene |
| 5 | 0 | 2 | -diino | pentadiino |
| 6 | 2 | 1 | -dienino | hexadienino |
| 10 | 2 | 2 | -diendiino | decadiendin |
Suffixes of radicals, ions and branches
Finally, when an alkane loses a hydrogen, it can be transformed into an alkyl radical, a cation, or an anion. These radicals or ions have the same formula of the branches in the branched hydrocarbons, for which reason both are named in the same way, and it consists of adding the suffix –yl to the prefix of the respective alkane.
Some examples of this type of radicals or ramifications together with their respective prefixes and suffixes are:
| number of carbons | Prefix | Suffix | Name |
| 1 | Met- | -ilo | Methyl Radical |
| 2 | Et- | -ilo | Ethyl Radical |
| 3 | Prop- | -ilo | Propyl radical |
| 4 | But- | -ilo | Butyl radical |
| 5 | Pent- | -ilo | pentyl radical |
| 6 | Hex- | -ilo | Hexyl Radical |
| 7 | Hept- | -ilo | Heptyl Radical |
| 8 | Oct- | -ilo | Octyl Radical |
| 9 | No N- | -ilo | Nonyl Radical |
| 10 | Dec- | -ilo | Decyl Radical |
References
- corner. (nd). Formulation and nomenclature of Alkanes, paraffins or saturated hydrocarbons . Retrieved from http://acorral.es/solucionario/quimica/alcanos.html
- Carey, F., & Giuliano, R. (2014). Organic Chemistry (9th ed .). Madrid, Spain: McGraw-Hill Interamericana de España SL
- Estelrich, AR (2018, May 23). Etymology of small molecule prefixes . Retrieved from https://oushia.com/etimologia-los-prefijos-las-moleculas-pequenas/
- Hekady. (2018, September 11). Alkanes from 1 to 100 names and formulas . Recovered from https://brainly.lat/tarea/10326110
- Couple, E. (2017). What are these called: “mono”, “bi”, “tri”, “tetra”, “penta”? –Quora . Retrieved from https://es.quora.com/C%C3%B3mo-se-llaman-estos-mono-bi-tri-tetra-penta
