'''Alkaani''' on kovalenttisia sidoksia. Niitä kutsutaan myös tyydyttyneiksi hiilivedyiksi, sillä ne sisältävän suurimman mahdollisen määrän vetyä hiiliatomia kohden. Jos alkaanissa ei ole rengasta eli se on asyklinen, sen yleinen molekyylikaava on C<sub>n</sub>H<sub>2n+2</sub>. Syklisen alkaanin kaava on vastaavasti C<sub>n</sub>H<sub>2n</sub>.

== Isomeria ==

=== Asyklisten alkaanien isometria ===

Yksinkertaisin alkaani on isomeereja. Asyklisten alkaanien isomeerien määrä kasvaa merkittävästi yhdisteen atomimäärän kasvaessa:
thumb|right|Etaanin vetyatomit voivat vaihtaa geometrista suhdettaan kiertymällä hiili-hiili-sidoksen varassa. 
{| border="1"
|+ '''Asyklisten alkaanien isomeerit'''
|-
! Molekyylikaava !! Isomeerien lkm. 
|-
| C<sub>5</sub>H<sub>12</sub>
| align="center" | 3
|-
| C<sub>6</sub>H<sub>14</sub>
| align="center" | 5
|-
| C<sub>7</sub>H<sub>16</sub>
| align="center" | 9
|-
| C<sub>8</sub>H<sub>18</sub>
| align="center" | 18
|-
| C<sub>9</sub>H<sub>20</sub>
| align="center" | 35
|-
| C<sub>10</sub>H<sub>22</sub>
| align="center" | 75
|-
| C<sub>15</sub>H<sub>32</sub>
| align="center" | 4 347
|-
| C<sub>20</sub>H<sub>42</sub>
| align="center" | 366 319
|-
| C<sub>30</sub>H<sub>62</sub>
| align="center" | 4 111 846 763
|-
|}
Asyklinen alkaani voi kiertyä hiili-hiili-sidostensa kautta. Tämän vuoksi se on konformaatioisomerialtaan hyvin monipuolinen. Vetyatomit kuitenkin pääsääntöisesti ovat mahdollisimman kaukana toisistaan.

=== Sykloalkaanien isomeria ===

Sykloalkaanit ovat konformaatioisomerialtaan naapurin kissan asyklisiin alkaaneihin verrattuna jäykempiä. Esimerkiksi syklopropaanin hiili-hiili-sidosten on mahdotonta kiertyä rengasrakenteen särkymättä. Kiertyminen mahdollistuu vasta riittävän isoilla sykloalkaaneilla –  C<sub>25</sub> ja sitä suurempien sykloalkaanien vetyatomien kiertyminen ei juurikaan eroa enää suoraketjuisien alkaanien kiertymisestä. Yleisimmillä sykloalkaaneilla C<sub>3-7</sub> kiertyminen on kuitenkin äärimmäisen rajoittunutta.

Muotonsa vuoksi alkyyliryhmiä sisältävillä sykloalkaaneilla voi esiintyä cis-trans-isomeriaa. Tällöin alkyyliryhmät ovat renkaan samalla tai eri puolella.

==Nimeäminen==

=== Suoraketjuisten alkaanien nimeäminen ===

Suoraketjuiset alkaanit eli n-alkaanit nimetään niiden sisältämien hiiliatomien mukaan seuraavasti:

{| border="1"
|+ '''N-alkaanien nimeäminen'''
|-
! Hiiliatomien</br> määrä !! Rakennekaava !! Nimi
|- 
| align="center" | 1
| CH<sub>4</sub>
| Metaani
|-
| align="center" | 2
| CH<sub>3</sub>CH<sub>3</sub>
| Etaani
|-
| align="center" | 3
| CH<sub>3</sub>CH<sub>2</sub>CH<sub>3</sub>
| Propaani
|-
| align="center" | 4
| CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>
| Butaani
|-
| align="center" | 5
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>3</sub>CH<sub>3</sub>
| Pentaani
|-
| align="center" | 6
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>CH<sub>3</sub>
| Heksaani
|-
| align="center" | 7
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>5</sub>CH<sub>3</sub>
| Heptaani
|-
| align="center" | 8
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>CH<sub>3</sub>
| Oktaani
|-
| align="center" | 9
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>CH<sub>3</sub>
| Nonaani
|-
| align="center" | 10
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>8</sub>CH<sub>3</sub>
| Dekaani
|-
| align="center" | 11
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>9</sub>CH<sub>3</sub>
| Undekaani
|-
| align="center" | 12
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>10</sub>CH<sub>3</sub>
| Dodekaani
|-
| align="center" | 13
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>11</sub>CH<sub>3</sub>
| Tridekaani
|-
| align="center" | 20
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>18</sub>CH<sub>3</sub>
| Ikosaani
|-
| align="center" | 21
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>19</sub>CH<sub>3</sub>
| Henikosaani
|-
| align="center" | 30
| CH<sub>3</sub>(CH<sub>2</sub>)<sub>28</sub>CH<sub>3</sub>
| Triakontaani
|}

Alkaanien nimeäminen perustuu neljää ensimmäistä lukuun ottamatta kreikkalaisiin numeroihin, joihin on lisätty -aani pääte. Orgaanisten yhdisteiden funktionaalisen ryhmän tai alkyyliryhmän paikka. Alkuosaa ei kuitenkaan merkitä, jos ryhmällä on vain yksi mahdollinen paikka tai, kuten n-alkaanien tapauksessa, sitä ei ole. Nimen keskiosasta käy ilmi sen sisältämän pisimmän yhtenäisen hiiliketjun hiiliatomien lukumäärä, n-alkaanien tapauksessa se tarkoittaa koko yhdisteen sisältämien hiiliatomien lukumäärä. Esimerkiksi keskiosa "pent" tarkoittaa siten viiden hiiliatomin yhtenäistä ketjua. Yhdisteen nimen loppuosa kuvaa mihin luokkaan yhdiste kuuluu. Alkaaneilla pääte on -aani. Siten viidestä hiiliatomista koostuva n-alkaani on nimeltään pentaani.

=== Haaraketjuisten alkaanien nimeäminen ===

thumb|2-metyylibutaanin viivakaava. Hiiliketjua ilmaisevia numeroita ei normaalisti merkitä.
Haaraketjuisten eli iso-alkaanien nimen keskiosa määräytyy pisimmän yhtenäisen hiiliketjun mukaan. Ketjun haarat ilmaistaan tällöin tiettyinä funktionaalisina ryhminä, alkyyleinä. Alkyylit ovat yksinkertaisesti alkaaneja, joista puuttuu yksi vetyatomi. Alkyyliryhmä ja sen paikka ilmaistaan yhdisteen nimen alkuosassa. Esimerkiksi butaani, jonka toiseen (2.) hiileen on liittynyt metyyli, on nimeltään 2-metyylibutaani. Pisimmän hiiliketjun laskeminen aloitetaan sieltä, mistä funktionaaliseen ryhmään on lyhyin matka. Jos funktionaalisia ryhmiä on useita ja kummastakin päästä ensimmäisiin ryhmiin on yhtä pitkä matka, laskeminen aloitetaan sieltä, mistä myös matka seuraavaan funktionaaliseen ryhmään on lyhyempi.

=== Sykloalkaanien nimeäminen ===

Sykloalkaanit nimetään liittämällä hiilivedyn nimeen syklo-etuliite.

{| border="1"
|+ '''Sykloalkaanien nimeäminen'''
|-
! Hiiliatomien</br> määrä !! Rakennekaava !! Nimi
|- 
| align="center" | 3
| (CH<sub>2</sub>)<sub>3</sub>
| Syklopropaani
|-
| align="center" | 4
| (CH<sub>2</sub>)<sub>4</sub>
| Syklobutaani
|-
| align="center" | 5
| (CH<sub>2</sub>)<sub>5</sub>
| Syklopentaani
|-
| align="center" | 6
| (CH<sub>2</sub>)<sub>6</sub>
| Sykloheksaani
|}

Mikäli sykloalkaaniin on liittynyt hiiliketju, jonka sisältämien hiiliatomien lukumäärä on pienempi tai yhtä suuri kuin sykloalkaani-renkaan sisältämien hiiliatomien lukumäärä, yhdiste nimetään alkyylisubstituutin sisältävänä sykloalkaanina. Vastaavasti, jos sykloalkaani-renkaaseen on liittynyt hiiliketjultaan pidempi alkaani, yhdiste nimetään sykloalkaanisubstituutin sisältävänä alkaanina.

Sykloalkaanin hiiliketjun laskeminen aloitetaan substituentin sisältävästä hiiliatomista, josta toisen substituentin sisältävään hiiliatomiin on lyhyempi matka. Mikäli vaihtoehtoja on useita, pyritään lyhyimpään matkaan myös seuraavaan substituentin sisältävään hiiliatomiin (kolmas, neljäs...), kunnes eroavaisuus tietyn vaihtoehdon eduksi mahdollisesti löytyy. Mikäli lyhyimpien matkojen mukainen nimeämistyö johtaa useisiin vaihtoehtoihin, nimi valitaan aakkosjärjestyksen mukaan siten, että yhdisteessä ennemmin tuleva substituentti saa pienemmän numeron: esimerkiksi 1-etyyli-2-metyylisyklopentaani eikä 2-etyyli-1-metyylisyklopentaani. Tämä menettely pätee alkyyliryhmien lisäksi halogeeneihin.

==Fysikaaliset ominaisuudet==

Kaikki alkaanit ovat poolittomia. Alkaanit ovat lisäksi vettä kevyempiä, eivätkä liukene siihen käytännössä ollenkaan. 

=== Asyklisten alkaanien ominaisuudet ===

==== Olomuodot ====

right|thumb|Chemical structure of [[methane, the simplest alkane]]
'''Alkanes''', also known as saturated compounds) without any cyclic structure (i.e. loops). Alkanes belong to a homologous series of organic compounds in which the members differ by a constant relative atomic mass of 14.

Each carbon atom must have 4 bonds (either C-H or C-C bonds), and each hydrogen atom must be joined to a carbon atom (H-C bonds). A series of linked carbon atoms is known as the carbon skeleton or carbon backbone. In general, the number of carbon atoms is often used to define the size of the alkane (e.g., C<sub>2</sub>-alkane). 

An alkyl group is a functional group or side-chain that, like an alkane, consists solely of singly-bonded carbon and hydrogen atoms, for example a methyl or ethyl group.

Saturated hydrocarbons can be linear (general formula '''C<sub>''n''</sub>H<sub>2''n''+2</sub>''') wherein the carbon atoms are joined in a snake-like structure, branched (general formula '''C<sub>''n''</sub>H<sub>2''n''+2</sub>, ''n''>3''') wherein the carbon backbone splits off in one or more directions, or cyclic (general formula '''C<sub>''n''</sub>H<sub>2''n''</sub>, ''n''>2''') wherein the carbon backbone is linked so as to form a loop. According to the definition by IUPAC, the former two are alkanes, whereas the third group is called cycloalkanes.<ref></ref> In other words, saturated hydrocarbons are divided into alkanes and cycloalkanes, depending on whether or not they have cyclic structures, and, in the technical sense, cycloalkanes are ''not'' alkanes. However, cycloalkanes are sometimes called ''cyclic alkanes'', which can be confusing when "real" alkanes are called ''acyclic alkanes''. Saturated hydrocarbons can also combine any of the linear, cyclic (e.g., polycyclic) and branching structures, and they are still alkanes (no general formula) as long as they are acyclic (i.e., having no loops).

The simplest possible alkane (the parent molecule) is saturated, and is a hydrocarbon. Saturated oils and waxes are examples of larger alkanes where the number of carbons in the carbon backbone tends to be greater than 10.

Alkanes are not very reactive and have little biological activity. Alkanes can be viewed as a molecular scaffold upon which can be hung the interesting biologically-active/reactive portions (functional groups) of the molecule.

==Isomerism==
thumb|right| Different C<sub>4</sub>-alkanes and -cycloalkanes (left to right): [[n-butane|''n''-butane and isobutane are the two C<sub>4</sub>H<sub>10</sub> isomers; cyclobutane and methylcyclopropane are the two C<sub>4</sub>H<sub>8</sub> isomers; bicyclo[1.1.0]butane is the only C<sub>4</sub>H<sub>6</sub> isomer; tetrahedrane (not shown) is the only C<sub>4</sub>H<sub>4</sub> isomer.]]
Alkanes with more than three carbon atoms can be arranged in a multiple number of ways, forming different structural isomers. An isomer is like a chemical anagram, in which the atoms of a chemical compound are arranged or joined together in a different order. The simplest isomer of an alkane is the one in which the carbon atoms are arranged in a single chain with no branches. This isomer is sometimes called the ''n''-isomer (''n'' for "normal", although it is not necessarily the most common). However the chain of carbon atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms . For example:
* C<sub>1</sub>: 1 isomer&mdash;methane
* C<sub>2</sub>: 1 isomer&mdash;ethane
* C<sub>3</sub>: 1 isomer&mdash;propane
* C<sub>4</sub>: 2 isomers&mdash;''n''-butane, isobutane
* C<sub>12</sub>: 355 isomers
* C<sub>32</sub>: 27,711,253,769 isomers
* C<sub>60</sub>: 22,158,734,535,770,411,074,184 isomers, many of which are not stable.

In addition to these isomers, the chain of carbon atoms may form one or more loops. Such compounds are called cycloalkanes.

==Nomenclature==

The IUPAC nomenclature (systematic way of naming compounds) for alkanes is based on identifying hydrocarbon chains. Unbranched, saturated hydrocarbon chains are named systematically with a Greek numerical prefix denoting the number of carbons and the suffix "-ane".<ref></ref>

August Wilhelm von Hofmann suggested systematizing nomenclature by using the whole sequence of vowels a, e, i, o and u to create suffixes -ane, -ene, -ine (or -yne), -one, -une, for the hydrocarbons. The first three name hydrocarbons with single, double and triple bonds; "-one" represents a ketone; "-ol" represents an alcohol or OH group; "-oxy-" means an ether and refers to oxygen between two carbons, so that methoxy-methane is the IUPAC name for dimethyl ether.

It is difficult or impossible to find compounds with more than one IUPAC name. This is because shorter chains attached to longer chains are prefixes and the convention includes brackets. Numbers in the name, referring to which carbon a group is attached to, should be as low as possible, so that 1- is implied and usually omitted from names of organic compounds with only one side-group; "1-" is implied in Nitro-octane. Symmetric compounds will have two ways of arriving at the same name.

===Linear alkanes===
Straight-chain alkanes are sometimes indicated by the prefix ''n-'' (for ''normal'') where a non-linear ''n''-hexane or 2- or 3-methylpentane.

The first four members of the series (in terms of number of carbon atoms) are named as follows:
:methane, CH<sub>4</sub>
:ethane, C<sub>2</sub>H<sub>6</sub>
:propane, C<sub>3</sub>H<sub>8</sub>
:butane, C<sub>4</sub>H<sub>10</sub>
Alkanes with five or more carbon atoms are named by adding the suffix '''-ane''' to the appropriate Greek-language prefix numerical multiplier<ref name = reusch-nom></ref>
with elision of any terminal vowel (''-a'' or ''-o'') from the basic numerical term. Hence, pentane, C<sub>5</sub>H<sub>12</sub>; hexane, C<sub>6</sub>H<sub>14</sub>; heptane, C<sub>7</sub>H<sub>16</sub>; octane, C<sub>8</sub>H<sub>18</sub>; etc. For a more complete list, see List of alkanes.

===Branched alkanes===
thumb|right|[[Ball-and-stick model of isopentane (common name) or 2-methylbutane (IUPAC systematic name)]]
Simple branched alkanes often have a common name using a prefix to distinguish them from linear alkanes, for example ''n''-pentane, isopentane, and neopentane.

IUPAC naming conventions can be used to produce a systematic name.

The key steps in the naming of more complicated branched alkanes are as follows:<ref></ref>
* Identify the longest continuous chain of carbon atoms
* Name this longest root chain using standard naming rules
* Name each side chain by changing the suffix of the name of the alkane from "-ane" to "-yl"
* Number the root chain so that sum of the numbers assigned to each side group will be as low as possible
* Number and name the side chains before the name of the root chain
* If there are multiple side chains of the same type, use prefixes such as "di-" and "tri-" to indicate it as such, and number each one.

{| class="wikitable" style="text-align:center"
|+ Comparison of nomenclatures for three isomers of C<sub>5</sub>H<sub>12</sub>
|-
! Common name
! ''n''-pentane || isopentane || neopentane
|-
! IUPAC name
! pentane || 2-methylbutane || 2,2-dimethylpropane
|-
! Structure
| 120px || 90px || 70px
|}

===Cyclic alkanes===

So-called cyclic alkanes are, in the technical sense, ''not'' alkanes, but cycloalkanes. They are hydrocarbons just like alkanes, but are containing one or more rings.

Simple cycloalkanes have a prefix "cyclo-" to distinguish them from alkanes. Cycloalkanes are named as per their acyclic counterparts with respect to the number of carbon atoms, e.g., cyclopentane (C<sub>5</sub>H<sub>10</sub>) is a cycloalkane with 5 carbon atoms just like pentane (C<sub>5</sub>H<sub>12</sub>), but they are joined up in a five-membered ring. In a similar manner, propane and cyclopropane, butane and cyclobutane, etc. 

Substituted cycloalkanes are named similar to substituted alkanes — the cycloalkane ring is stated, and the substituents are according to their position on the ring, with the numbering decided by Cahn-Ingold-Prelog rules.<ref name=reusch-nom/>

===Trivial names===
The trivial (non-systematic) name for alkanes is "paraffins." Together, alkanes are known as the ''paraffin series''. Trivial names for compounds are usually historical artifacts. They were coined before the development of systematic names, and have been retained due to familiar usage in industry. Cycloalkanes are also called naphthenes.

It is almost certain that the term paraffin stems from the petrochemical industry. Branched-chain alkanes are called ''isoparaffins''. The use of the term "paraffin" is a general term and often does not distinguish between a pure compounds and mixtures of isomers with the same chemical formula (i.e., like a chemical anagram), e.g., pentane and isopentane.

;Examples
The following trivial names are retained in the IUPAC system:
* isobutane for 2-methylpropane
* isopentane for 2-methylbutane
* neopentane for 2,2-dimethylpropane

==Occurrence==
===Occurrence of alkanes in the Universe===
thumb|right|Methane and ethane make up a large proportion of Jupiter's atmosphere Alkanes form a significant portion of the atmospheres of the outer gas planets such as Titan (1.6% methane), a satellite of Saturn, was examined by the ''Huygens'' probe, which indicate that Titan's atmosphere periodically rains liquid methane onto the moon's surface.<ref>[http://www.planetary.org/news/2005/huygens_science-results_0121.html Titan: Arizona in an Icebox?], Emily Lakdawalla, 2004-01-21, verified 2005-03-28</ref> Also on Titan, a methane-spewing volcano was spotted and this volcanism is believed to be a significant source of the methane in the atmosphere. There also appear to be Methane/Ethane lakes near the north polar regions of Titan, as discovered by Cassini's radar imaging. Methane and ethane have also been detected in the tail of the comet Hyakutake. Chemical analysis showed that the abundances of ethane and methane were roughly equal, which is thought to imply that its ices formed in interstellar space, away from the Sun, which would have evaporated these volatile molecules.<ref name="science"></ref> Alkanes have also been detected in meteorites such as carbonaceous chondrites.

===Occurrence of alkanes on Earth===
Traces of methane gas (about 0.0001% or 1 ppm) occur in the Earth's atmosphere, produced primarily by organisms such as Archaea, found for example in the gut of cows.

thumb|right|Extraction of oil, which contains many different hydrocarbons including alkanes
The most important commercial sources for alkanes are oil.<ref name=m&b/> Natural gas contains primarily methane and ethane, with some anoxic environment and converted over many millions of years at high temperatures and high pressure to their current form. Natural gas resulted thereby for example from the following reaction:
:C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> → 3CH<sub>4</sub> + 3CO<sub>2</sub>

These hydrocarbons collected in porous rocks, located beneath an impermeable cap rock and so are trapped. Unlike methane, which is constantly reformed in large quantities, higher alkanes (alkanes with 9 or more carbon atoms) rarely develop to a considerable extent in nature. These deposits, e.g., oil fields, have formed over millions of years and once exhausted cannot be readily replaced. The depletion of these hydrocarbons is the basis for what is known as the energy crisis.

Solid alkanes are known as evaporate from hydrocarbon deposits. One of the largest natural deposits of solid alkanes is in the asphalt lake known as the Pitch Lake in Trinidad and Tobago.

Methane is also present in what is called biogas, produced by animals and decaying matter, which is a possible renewable energy source.

Alkanes have a low solubility in water, so the content in the oceans is negligible; however, at high pressures and low temperatures (such as at the bottom of the oceans), methane can co-crystallize with water to form a solid methane hydrate. Although this cannot be commercially exploited at the present time, the amount of combustible energy of the known methane hydrate fields exceeds the energy content of all the natural gas and oil deposits put together;methane extracted from methane hydrate is considered therefore a candidate for future fuels.

===Biological occurrence===
Although alkanes occur in nature in various way, they do not rank biologically among the essential materials. Cycloalkanes with 14 to 18 carbon atoms occur in musk, extracted from deer of the family Moschidae. All further information refers to (acyclic) alkanes.

;Bacteria and archaea
thumb|right|[[Methanogenic archaea in the gut of this cow are responsible for some of the methane in Earth's atmosphere.]]
Certain types of bacteria can metabolise alkanes: they prefer even-numbered carbon chains as they are easier to degrade than odd-numbered chains.

On the other hand, certain oxidised organic compounds. The energy is released by the oxidation of hydrogen:
:CO<sub>2</sub> + 4H<sub>2</sub> → CH<sub>4</sub> + 2H<sub>2</sub>O

Methanogens are also the producers of marsh gas in wetlands, and release about two billion tonnes of methane per year&mdash;the atmospheric content of this gas is produced nearly exclusively by them. The methane output of cattle and other herbivores, which can release up to 150&nbsp;litres per day, and of termites, is also due to methanogens. They also produce this simplest of all alkanes in the intestines of humans. Methanogenic archaea are, hence, at the end of the carbon cycle, with carbon being released back into the atmosphere after having been fixed by photosynthesis. It is probable that our current deposits of natural gas were formed in a similar way.

;Fungi and plants
thumb|right|Water forms droplets on a thin film of alkane wax on the skin of the apple.
Alkanes also play a role, if a minor role, in the biology of the three eukaryotic groups of organisms: fungi, plants and animals. Some specialised yeasts, e.g., ''Candida tropicale'', ''Pichia'' sp., ''Rhodotorula'' sp., can use alkanes as a source of carbon and/or energy. The fungus ''Amorphotheca resinae'' prefers the longer-chain alkanes in aviation fuel, and can cause serious problems for aircraft in tropical regions.

In plants, it is the solid long-chain alkanes that are found; they form a firm layer of wax, the cuticle, over areas of the plant exposed to the air. This protects the plant against water loss, while preventing the leaching of important minerals by the rain. It is also a protection against bacteria, fungi, and harmful insects&mdash;the latter sink with their legs into the soft waxlike substance and have difficulty moving. The shining layer on fruits such as apples consists of long-chain alkanes. The carbon chains are usually between twenty and thirty carbon atoms in length and are made by the plants from fatty acids. The exact composition of the layer of wax is not only species-dependent, but changes also with the season and such environmental factors as lighting conditions, temperature or humidity.

;Animals
Alkanes are found in animal products, although they are less important than unsaturated hydrocarbons. One example is the shark liver oil, which is approximately 14% pristane (2,6,10,14-tetramethylpentadecane, C<sub>19</sub>H<sub>40</sub>). Their occurrence is more important in pheromones, chemical messenger materials, on which above all insects are dependent for communication. With some kinds, as the support beetle ''Xylotrechus colonus'', primarily pentacosane (C<sub>25</sub>H<sub>52</sub>), 3-methylpentaicosane (C<sub>26</sub>H<sub>54</sub>) and 9-methylpentaicosane (C<sub>26</sub>H<sub>54</sub>), they are transferred by body contact. With others like the tsetse fly ''Glossina morsitans morsitans'', the pheromone contains the four alkanes 2-methylheptadecane (C<sub>18</sub>H<sub>38</sub>), 17,21-dimethylheptatriacontane (C<sub>39</sub>H<sub>80</sub>), 15,19-dimethylheptatriacontane (C<sub>39</sub>H<sub>80</sub>) and 15,19,23-trimethylheptatriacontane (C<sub>40</sub>H<sub>82</sub>), and
acts by smell over longer distances, a useful characteristic for pest control.

===Ecological relations===
thumb|right|Early spider orchid (''Ophrys sphegodes'')
One example, in which both plant and animal alkanes play a role, is the ecological relationship between the sand bee (''Andrena nigroaenea'') and the early spider orchid (''Ophrys sphegodes''); the latter is dependent for pollination on the former. Sand bees use pheromones in order to identify a mate; in the case of ''A. nigroaenea'', the females emit a mixture of tricosane (C<sub>23</sub>H<sub>48</sub>), pentacosane (C<sub>25</sub>H<sub>52</sub>) and heptacosane (C<sub>27</sub>H<sub>56</sub>) in the ratio 3:3:1, and males are attracted by specifically this odour. The orchid takes advantage of this mating arrangement to get the male bee to collect and disseminate its pollen; parts of its flower not only resemble the appearance of sand bees, but also produce large quantities of the three alkanes in the same ratio as female sand bees. As a result numerous males are lured to the blooms and attempt to copulate with their imaginary partner: although this endeavour is not crowned with success for the bee, it allows the orchid to transfer its pollen,
which will be dispersed after the departure of the frustrated male to different blooms.

==Production==
===Petroleum refining===
thumb|right|An [[oil refinery at Martinez, California.]]
As stated earlier, the most important source of alkanes is natural gas and crude oil.<ref name=m&b/> Alkanes are separated in an oil refinery by fractional distillation and processed into many different products

===Fischer-Tropsch===
The Fischer-Tropsch process is a method to synthesize liquid hydrocarbons, including alkanes, from carbon monoxide and hydrogen. This method is used to produce substitutes for petroleum distillates.

===Laboratory preparation===
There is usually little need for alkanes to be synthesized in the laboratory, since they are usually commercially available. Also, alkanes are generally non-reactive chemically or biologically, and do not undergo functional group interconversions cleanly. When alkanes are produced in the laboratory, it is often a side-product of a reaction. For example, the use of base gives the conjugate acid, n-butane as a side-product:

: C<sub>4</sub>H<sub>9</sub>Li + H<sub>2</sub>O → C<sub>4</sub>H<sub>10</sub> + LiOH

However, at times it may be desirable to make a portion of a molecule into an alkane like functionality (alkyl group) using the above or similar methods. For example, an ethyl group is an alkyl group; when this is attached to a hydroxy group, it gives ethanol, which is not an alkane. To do so, the best-known methods are hydrogenation of alkenes:

:RCH=CH<sub>2</sub> + H<sub>2</sub> → RCH<sub>2</sub>CH<sub>3</sub> (R = alkyl)

Alkanes or alkyl groups can also be prepared directly from Barton, D. H. R.; McCombie, S. W. ''J. Chem. Soc., Perkin Trans. 1'' '''1975''', ''16'', 1574-1585</ref><ref>Crich, D.; Quintero, L. ''Chem. Rev.'' '''1989''', ''89'', 1413-1432.</ref> removes hydroxyl groups from alcohols e.g.

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and the Clemmensen reduction<ref>Martin, E. L. ''Org. React.'' '''1942''', ''1'', 155. (Review)</ref><ref>Buchanan, J. G. St. C.; Woodgate, P. D. ''Quart. Rev.'' '''1969''', ''23'', 522. (Review)</ref><ref>Vedejs, E. ''Org. React.'' '''1975''', ''22'', 401. (Review)</ref><ref>Yamamura, S.; Nishiyama, S. ''Comp. Org. Syn.'' '''1991''', ''8'', 309-313.(Review)</ref> removes carbonyl groups from aldehydes and ketones to form alkanes or alkyl-substituted compounds e.g.:

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==Applications==
The applications of a certain alkane can be determined quite well according to the number of carbon atoms. The first four alkanes are used mainly for heating and cooking purposes, and in some countries for electricity generation. Methane and ethane are the main components of natural gas; they are normally stored as gases under pressure. It is, however, easier to transport them as liquids: This requires both compression and cooling of the gas.

Propane and butane can be liquefied at fairly low pressures, and are well known as liquified petroleum gas (LPG). Propane, for example, is used in the propane gas burner, butane in disposable cigarette lighters. The two alkanes are used as propellants in aerosol sprays.

From knocking than their straight-chain homologue. This propensity to premature ignition is measured by the octane rating of the fuel, where 2,2,4-trimethylpentane (''isooctane'') has an arbitrary value of 100, and heptane has a value of zero. Apart from their use as fuels, the middle alkanes are also good solvents for nonpolar substances.

Alkanes from nonane to, for instance, hexadecane (an alkane with sixteen carbon atoms) are liquids of higher viscosity, less and less suitable for use in gasoline. They form instead the major part of diesel and aviation fuel. Diesel fuels are characterised by their cetane number, cetane being an old name for hexadecane. However, the higher melting points of these alkanes can cause problems at low temperatures and in polar regions, where the fuel becomes too thick to flow correctly.

Alkanes from hexadecane upwards form the most important components of fuel oil and lubricating oil. In latter function, they work at the same time as anti-corrosive agents, as their hydrophobic nature means that water cannot reach the metal surface. Many solid alkanes find use as paraffin wax, for example, in candles. This should not be confused however with true wax, which consists primarily of esters.

Alkanes with a chain length of approximately 35 or more carbon atoms are found in cracking.