View source for Cycloalkane

{{Short description|Saturated alicyclic hydrocarbon}}
[[Image:Cyclobutane-buckled-3D-balls.png|thumb|right|Ball-and-stick model of [[cyclobutane]]]]
In [[organic chemistry]], the '''cycloalkanes''' (also called '''naphthenes''', but distinct from [[naphthalene]]) are the [[ring (chemistry)|monocyclic]] [[Saturated and unsaturated compounds|saturated]] [[hydrocarbons]].<ref>{{GoldBookRef |title=Cycloalkane|file=C01497|year=2014}}</ref> In other words, a cycloalkane consists only of [[hydrogen]] and [[carbon]] atoms arranged in a structure containing a single ring (possibly with [[side chains]]), and all of the carbon-carbon bonds are [[single bond|single]].  The larger cycloalkanes, with more than 20 <!--this could be less, now that I think about it the information in the [[paraffin]] article could be wrong, or not apply to the ring varieties --> carbon atoms are typically called '''''cycloparaffins'''''. All cycloalkanes are isomers of [[alkenes]].<ref name="MSU">{{Cite web|title=Alkanes & Cycloalkanes|url=https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/chapt5.htm|access-date=2022-02-20|website=www2.chemistry.msu.edu}}</ref>

The cycloalkanes without side chains (also known as '''monocycloalkanes''') are classified as small ([[cyclopropane]] and [[cyclobutane]]), common ([[cyclopentane]], [[cyclohexane]], and [[cycloheptane]]), medium ([[cyclooctane]] through [[cyclotridecane]]), and large (all the rest). <!--The need for the delineation between medium and large rings, is that ring strain is zero for all rings with 14 or more members, i.e. the large rings -->

Besides this standard definition by [[IUPAC|the International Union of Pure and Applied Chemistry]] (IUPAC), in some authors' usage the term ''cycloalkane'' includes also those saturated hydrocarbons that are polycyclic.<ref name="MSU"/>
In any case, the general form of the [[chemical formula]] for cycloalkanes is C<sub>''n''</sub>H<sub>2(''n''+1−''r'')</sub>, where ''n'' is the number of carbon atoms and ''r'' is the number of rings. The simpler form for cycloalkanes with only one ring is C<sub>''n''</sub>H<sub>2''n''</sub>.

==Examples==
<gallery>
File:Cyclopropane.svg|[[Cyclopropane]]
File:Cyclobutane-compressed.svg|[[Cyclobutane]]
File:Cyclopentane.svg|[[Cyclopentane]]
File:Cyclohexane-2D-skeletal.svg|[[Cyclohexane]]
File:Cycloheptane 200.svg|[[Cycloheptane]]
File:Cyclooctane crown conformation.svg|[[Cyclooctane]]
</gallery>

== Nomenclature ==
{{See also|IUPAC nomenclature}}
{{See also|Alkanes}}

[[Image:Norbornane-2D-skeletal.png|thumb|[[Norbornane]] (also called ''bicyclo[2.2.1]heptane'')]]
Unsubstituted cycloalkanes that contain a single ring in their molecular structure are typically named by adding the prefix "cyclo" to the name of the corresponding linear [[alkane]] with the same number of [[carbon]] atoms in its chain as the cycloalkane has in its ring. For example, the name of [[cyclopropane]] (C<sub>3</sub>H<sub>6</sub>) containing a three-membered ring is derived from [[propane]] (C<sub>3</sub>H<sub>8</sub>) - an [[alkane]] having three [[carbon]] atoms in the main chain. 

The naming of polycyclic alkanes such as [[Bicyclic compound|bicyclic]] alkanes and [[Spiro compound|spiro]] alkanes is more complex, with the base name indicating the number of carbons in the ring system, a prefix indicating the number of rings ( "''bicyclo''-" or "''spiro''-"), and a numeric prefix before that indicating the number of carbons in each part of each ring, exclusive of junctions. For instance, a bicyclooctane that consists of a six-membered ring and a four-membered ring, which share two adjacent carbon atoms that form a shared edge, is [4.2.0]-bicyclooctane. That part of the six-membered ring, exclusive of the shared edge has 4 carbons. That part of the four-membered ring, exclusive of the shared edge, has 2 carbons. The edge itself, exclusive of the two vertices that define it, has 0 carbons.

There is more than one convention (method or nomenclature) for the naming of compounds, which can be confusing for those who are just learning, and inconvenient for those who are well-rehearsed in the older ways. For beginners, it is best to learn IUPAC nomenclature from [[IUPAC Blue Book|a source that is up to date]],<ref>{{Cite web |title=Blue Book |url=https://iupac.qmul.ac.uk/BlueBook/PDF/ |access-date=2023-04-01 |website=iupac.qmul.ac.uk}}</ref> because this system is constantly being revised. In the above example [4.2.0]-bicyclooctane would be written bicyclo[4.2.0]octane to fit the conventions for IUPAC naming. It then has room for an additional numerical prefix if there is the need to include details of other attachments to the molecule such as chlorine or a methyl group. Another convention for the naming of compounds is the ''common name'', which is a shorter name and it gives less information about the compound. An example of a common name is [[terpineol]], the name of which can tell us only that it is an alcohol (because the suffix "-ol" is in the name) and it should then have a [[hydroxyl group]] (–OH) attached to it.

The IUPAC naming system for organic compounds can be demonstrated using the example provided in the adjacent image. The base name of the compound, indicating the total number of carbons in both rings (including the shared edge), is listed first. For instance, "heptane" denotes "hepta-", which refers to the seven carbons, and "-ane", indicating single bonding between carbons. Next, the numerical prefix is added in front of the base name, representing the number of carbons in each ring (excluding the shared carbons) and the number of carbons present in the bridge between the rings. In this example, there are two rings with two carbons each and a single bridge with one carbon, excluding the carbons shared by both the rings. The prefix consists of three numbers that are arranged in descending order, separated by dots: [2.2.1]. Before the numerical prefix is another prefix indicating the number of rings (e.g., "bicyclo+"). Thus, the name is bicyclo[2.2.1]heptane.

Cycloalkanes as a group are also known as '''naphthenes''', a term mainly used in the [[petroleum]] industry.<ref>{{cite book |doi=10.1016/C2009-0-16348-1 |title=Fundamentals of Petroleum Refining |date=2010 |isbn=978-0-444-52785-1 |vauthors=Fahim, MA etal |page=14 |url=https://books.google.com/books?id=UcFsv1mMFHIC&q=naphthenes }}</ref>

== Properties ==
Containing only C–C and C–H bonds, cycloalkanes are similar to alkanes in their general properties. Cycloalkanes with high angle strain, such as cyclopropane, have weaker C–C bonds, promoting ring-opening reactions.

Cycloalkanes have higher [[boiling point]]s, [[melting point]]s, and [[density|densities]] than alkanes. This is due to stronger [[London forces]] because the ring shape allows for a larger area of contact.

Even-numbered cycloalkanes tend to have higher melting points than odd-numbered cycloalkanes. While variations in [[enthalpy]] and orientational [[entropy]] of the solid-phase crystal structure largely explain the odd-even alternation found in [[Alkane#Melting points|alkane melting points]],<ref>{{cite journal | last=Boese | first=Roland | last2=Weiss | first2=Hans-Christoph | last3=Bläser | first3=Dieter | title=The Melting Point Alternation in the Short-Chain ''n''-Alkanes: Single-Crystal X-Ray Analyses of Propane at 30&nbsp;K and of ''n''-Butane to ''n''-Nonane at 90&nbsp;K | journal=Angewandte Chemie International Edition | volume=38 | issue=7 | date=1999-04-01 | issn=1433-7851 | doi=10.1002/(SICI)1521-3773(19990401)38:7<988::AID-ANIE988>3.0.CO;2-0 | pages=988–992}}</ref><ref name=Brown2000>{{cite journal |last1=Brown |first1=RJC |last2=Brown |first2=RFC |title=Melting Point and Molecular Symmetry |journal=Journal of Chemical Education |date=June 2000 |volume=77 |issue=6 |pages=724 |doi=10.1021/ed077p724}}</ref> conformational entropy of the solid and liquid phases has a large impact on cycloalkane melting points.<ref name="Dale1963c">{{cite journal |last1=Dale |first1=Johannes |title=15. Macrocyclic compounds. Part III. Conformations of cycloalkanes and other flexible macrocycles |journal=Journal of the Chemical Society (Resumed) |date=1963 |pages=93–111 |doi=10.1039/JR9630000093}}</ref>{{rp|p=98}}<ref name=condis>{{cite book |author-last1=Wunderlich |author-first1=Bernhard |author-last2=Möller |author-first2=Martin |author-last3=Grebowicz |author-first3=Janusz |author-last4=Baur |author-first4=Herbert |title=Conformational Motion and Disorder in Low and High Molecular Mass Crystals |date=1988 |publisher=Springer-Verlag Springer e-books |location=Berlin, Heidelberg |isbn=978-3-540-38867-8 |chapter=Condis crystals of cyclic alkanes, silanes and related compounds |pages=26–44 |doi=10.1007/BFb0008610}}</ref> For example, cycloundecane has a large number of accessible conformers near room temperature, giving it a low melting point,<ref name=Dragojlovic/>{{rp|p=22}} whereas cyclododecane adopts a single lowest-energy conformation<ref name=Dragojlovic/>{{rp|p=25}} (up to [[chirality]]) in both the liquid phase and solid phase (above 199&nbsp;K),<ref name=condis/>{{rp|p=32–34}} and has a high melting point. These trends are broken from cyclopentadecane onwards, due to increasing variation in solid-phase conformational mobility, though higher cycloalkanes continue to display large odd-even fluctuations in their [[plastic crystal]] transition temperatures.<ref name="Dale1963c"/>{{rp|pp=99–100}} Sharp plastic crystal [[phase transition]]s disappear from {{chem2|C48H96}} onwards, and sufficiently high molecular weight cycloalkanes, such as {{chem2|C288H576}}, have similar crystal lattices and melting points to [[high-density polyethylene]].<ref name=condis/>{{rp|pp=27,37}}

=== Table of cycloalkanes ===
{| class="wikitable sortable"
! Alkane
! Formula
! Melting point [°C]
! Boiling point [°C]
! Liquid density [g·cm<sup>−3</sup>] (at 20&nbsp;°C)
|-
|[[Cyclopropane]]
|C<sub>3</sub>H<sub>6</sub>
| −127.6<ref name=condis/>{{rp|p=27}}
| −33
|
|-
|[[Cyclobutane]]
|C<sub>4</sub>H<sub>8</sub>
| −90.7<ref name=condis/>{{rp|p=27}}
| 12.5
| 0.720
|-
|[[Cyclopentane]]
|C<sub>5</sub>H<sub>10</sub>
| −93.4<ref name=condis/>{{rp|p=27}}
| 49.2
| 0.751
|-
|[[Cyclohexane]]
|C<sub>6</sub>H<sub>12</sub>
| 6.7<ref name=condis/>{{rp|p=27}}
| 80.7
| 0.778
|-
|[[Cycloheptane]]
|C<sub>7</sub>H<sub>14</sub>
| −8.0<ref name=condis/>{{rp|p=27}}
| 118.4
| 0.811
|-
|[[Cyclooctane]]
|C<sub>8</sub>H<sub>16</sub>
| 14.5<ref>{{cite web |title=ECHA CHEM |url=https://chem.echa.europa.eu/100.005.484/dossier-view/3e1667e8-ea5d-4ddf-97cc-3cdac851bc16/80062f6b-8b88-4fc0-bd92-5011cb0d3746_f73f2ad6-9144-4fac-984d-885c4fec7b63 |website=chem.echa.europa.eu}}</ref>
| 151.2<ref>{{cite web |title=ECHA CHEM |url=https://chem.echa.europa.eu/100.005.484/dossier-view/3e1667e8-ea5d-4ddf-97cc-3cdac851bc16/5978e774-6b57-4c45-8172-78863845d50d_f73f2ad6-9144-4fac-984d-885c4fec7b63 |website=chem.echa.europa.eu}}</ref>
| 0.840<ref>{{cite web |title=ECHA CHEM |url=https://chem.echa.europa.eu/100.005.484/dossier-view/3e1667e8-ea5d-4ddf-97cc-3cdac851bc16/0521449b-092d-4883-9121-2459ff0a21c7_f73f2ad6-9144-4fac-984d-885c4fec7b63 |website=chem.echa.europa.eu}}</ref>
|-
|[[Cyclononane]]
|C<sub>9</sub>H<sub>18</sub>
| 10–11<ref name=Kaarsemaker1952>{{cite journal |last1=Kaarsemaker |first1=Sj. |last2=Coops |first2=J. |title=Thermal quantities of some cycloparaffins. Part III. results of measurements |journal=Recueil des Travaux Chimiques des Pays-Bas |date=January 1952 |volume=71 |issue=3 |pages=261–276 |doi=10.1002/recl.19520710307}}</ref>{{rp|p=262}}
| 178<ref name=Kaarsemaker1952/>{{rp|p=265}}
| 0.8534
|-
|[[Cyclodecane]]
|C<sub>10</sub>H<sub>20</sub>
| 9.9<ref name=condis/>{{rp|p=27}}
| 201
| 0.871
|-
|[[Cycloundecane]]
|C<sub>11</sub>H<sub>22</sub>
| −7.2<ref>{{cite journal |last1=Ruzicka |first1=L |author-link1=Leopold Ružička |last2=Plattner |first2=PA |last3=Wild |first3=H |title=209. Zur Kenntnis des Kohlenstoffringes. (40. Mitteilung). Über die Schmelzpunkte in der Reihe der Polymethylen-Kohlenwasserstoffe von Cyclo-propan bis Cyclo-octadecan |trans-title=209. On carbon rings. (Part 40). On the melting points in the series of polymethylene hydrocarbons from cyclopropane to cyclooctadecane |lang=de |journal=[[Helvetica Chimica Acta]] |date=January 1946 |volume=29 |issue=6 |pages=1611–1615 |doi=10.1002/hlca.19460290631}}</ref>{{rp|p=1613}}
| 179–181<ref name="Egloff"/>{{rp|p=142}}
| 0.81<ref name="Egloff">{{cite book |last1=Egloff |first1=Gustav |author-link1=Gustav Egloff |title=Physical constants of hydrocarbons. Vol. 2 : Cyclanes, cyclenes, cyclynes, and other alicyclic hydrocarbons |date=1940 |publisher=Reinhold Publishing Corporation |url=https://archive.org/details/physicalconstant030969mbp}}</ref>{{rp|p=142}}
|-
|[[Cyclododecane]]
|C<sub>12</sub>H<sub>24</sub>
| 60.4<ref>{{cite web |title=ECHA CHEM |url=https://chem.echa.europa.eu/100.005.486/dossier-view/48fb0c95-bec2-454d-bc38-2d3bde522825/IUC5-aac305f0-c810-4d61-aeae-f66f6b00fc4c_40cc91bb-88f0-4232-9284-1490cbdfbe2e |website=chem.echa.europa.eu}}</ref>
| 244.0<ref>{{cite web |title=ECHA CHEM |url=https://chem.echa.europa.eu/100.005.486/dossier-view/48fb0c95-bec2-454d-bc38-2d3bde522825/IUC5-fb10790e-5b4f-420a-a45e-8ff674cc8627_40cc91bb-88f0-4232-9284-1490cbdfbe2e |website=chem.echa.europa.eu}}</ref>
| 0.855 (extrapolated)<ref>{{cite web |title=ECHA CHEM |url=https://chem.echa.europa.eu/100.005.486/dossier-view/48fb0c95-bec2-454d-bc38-2d3bde522825/IUC5-2078b800-f50b-4203-a30f-dc4deed97c3a_40cc91bb-88f0-4232-9284-1490cbdfbe2e |website=chem.echa.europa.eu |quote=The density of cyclododecane was measured at 8 temperatures between 66 and 134 °C with a dilatometer. Extrapolation to 20 °C leads to 0.855 g·cm<sup>−3</sup>.}}</ref>
|-
|[[Cyclotridecane]]
|C<sub>13</sub>H<sub>26</sub>
| 24.5<ref name=condis/>{{rp|p=27}}
| <!--112–113 (at 9&nbsp;Torr)-->
| 0.861<ref name=Egloff/>{{rp|p=143}}{{efn|Liquid-phase density measured for a sample melting at 18&nbsp;°C. The same sample was measured to have a solid density of 0.864 g·cm<sup>−3</sup> at 16&nbsp;°C.}}
|-
|[[Cyclotetradecane]]
|C<sub>14</sub>H<sub>28</sub>
| 56.2<ref name=condis/>{{rp|p=27}}
| <!--131 (at 11&nbsp;Torr)-->
| <!--0.83 (at 75&nbsp;°C)<ref name=Egloff/>{{rp|p=143}}-->
|-
|[[Cyclopentadecane]]
|C<sub>15</sub>H<sub>30</sub>
| 63.5<ref name=condis/>{{rp|p=27}}
| <!--45–60 (at 5&nbsp;Torr)-->
| <!--0.8364 (at 61.5&nbsp;°C)<ref name="Ruzicka1926">{{cite journal |last1=Ruzicka |first1=L. |author-link1=Leopold Ružička |last2=Brugger |first2=W. |last3=Pfeiffer |first3=M. |last4=Schinz |first4=H. |last5=Stoll |first5=M. |title=Zur Kenntnis des Kohlenstoffringes VI. Über die relative Bildungsleichtigkeit, die relative Beständigkeit und den räumlichen Bau der gesättigten Kohlenstoffringe |trans-title=On carbon rings VI. On the relative ease of formation, the relative stability and the spatial structure of the saturated carbon rings |lang=de |journal=[[Helvetica Chimica Acta]] |date=January 1926 |volume=9 |issue=1 |pages=499–520 |doi=10.1002/hlca.19260090164}}</ref>{{rp|p=518}}-->
|-
|[[Cyclohexadecane]]
|C<sub>16</sub>H<sub>32</sub>
| 60.6<ref name=condis/>{{rp|p=27}}
| 319
| <!--0.82 (at 72&nbsp;°C)<ref name=Egloff/>{{rp|p=144}}-->
|-
|[[Cycloheptadecane]]
|C<sub>17</sub>H<sub>34</sub>
| 64–67<ref name=Dale1963a/>
|
| <!--0.82 (at 77&nbsp;°C)<ref name=Egloff/>{{rp|p=145}}-->
|-
|[[Cyclooctadecane]]
|C<sub>18</sub>H<sub>36</sub>
| 74–75<ref name=Dale1963a/>
|
| <!--0.82 (at 76&nbsp;°C)<ref name=Egloff/>{{rp|p=145}}-->
|-
|[[Cyclononadecane]]
|C<sub>19</sub>H<sub>38</sub>
| 79–82<ref name=Dale1963a>{{cite journal |last1=Dale |first1=Johannes |last2=Hubert |first2=A. J. |last3=King |first3=G. S. D. |title=13. Macrocyclic compounds. Part I. Synthesis of macrocyclic polyynes: conformational effects in ring formation and in physical properties |journal=Journal of the Chemical Society (Resumed) |date=1963 |page=77 |doi=10.1039/JR9630000073}}</ref>
|
|
|-
|[[Cycloeicosane]]
|C<sub>20</sub>H<sub>40</sub>
| 49.9<ref name=condis/>{{rp|p=27}}{{efn|Dale et al. (1963) instead gives a melting point of 61–62&nbsp;°C.<ref name=Dale1963a/>}}
|
|
|}

== Conformations and ring strain ==
{{Main|Strain (chemistry)}}
In cycloalkanes, the carbon atoms are ''sp''<sup>3</sup> [[orbital hybridization|hybridized]], which would imply an ideal [[Tetrahedral molecular geometry#Tetrahedral bond angle|tetrahedral bond angle]] of 109°&nbsp;28{{prime}} whenever possible. Owing to evident geometrical reasons, rings with 3, 4, and (to a small extent) also 5 atoms can only afford narrower angles; the consequent deviation from the ideal tetrahedral bond angles causes an increase in potential energy and an overall destabilizing effect. Eclipsing of hydrogen atoms is an important destabilizing effect, as well. The [[Ring strain#Angle_strain_(Baeyer_strain)|strain energy]] of a cycloalkane is the increase in energy caused by the compound's geometry, and is calculated by comparing the experimental [[standard enthalpy change of combustion]] of the cycloalkane with the value calculated using average bond energies. Molecular mechanics calculations are well suited to identify the many conformations occurring particularly in medium rings.<ref name=Dragojlovic>{{cite journal |doi=10.1007/s40828-015-0014-0 |url=https://link.springer.com/content/pdf/10.1007/s40828-015-0014-0.pdf |title=Conformational analysis of cycloalkanes |year=2015 |last1=Dragojlovic |first1=Veljko |journal=Chemtexts |volume=1 |issue=3 |page=14 |bibcode=2015ChTxt...1...14D |s2cid=94348487 }}</ref>{{rp|pp=16–23}}

Ring strain is highest for [[cyclopropane]], in which the carbon atoms form a triangle and therefore have {{not a typo|60°}} C–C–C bond angles. There are also three pairs of eclipsed hydrogens. The ring strain is calculated to be around 120&nbsp;kJ&nbsp;mol<sup>&minus;1</sup>.

[[Cyclobutane]] has the carbon atoms in a puckered square with approximately 90° bond angles; "puckering" reduces the eclipsing interactions between hydrogen atoms. Its ring strain is therefore slightly less, at around 110&nbsp;kJ&nbsp;mol<sup>&minus;1</sup>.

For a theoretical planar [[cyclopentane]] the C–C–C bond angles would be 108°, very close to the measure of the tetrahedral angle. Actual cyclopentane molecules are puckered, but this changes only the bond angles slightly so that angle strain is relatively small. The eclipsing interactions are also reduced, leaving a ring strain of about 25&nbsp;kJ&nbsp;mol<sup>&minus;1</sup>.<ref>{{cite book |last1=McMurry |first1=John |title=Organic chemistry |date=2000 |publisher=Brooks/Cole |location=Pacific Grove, CA |isbn=0534373674 |pages=126 |edition=5th}}</ref>

In [[cyclohexane]] the ring strain and eclipsing interactions are negligible because the puckering of the ring allows ideal tetrahedral bond angles to be achieved. In the most stable ''chair form'' of cyclohexane, axial hydrogens on adjacent carbon atoms are pointed in opposite directions, virtually eliminating eclipsing strain. 
In medium-sized rings (7 to 13 carbon atoms) conformations in which the angle strain is minimised create [[transannular strain]] or [[Pitzer strain]]. At these ring sizes, one or more of these sources of strain must be present, resulting in an increase in strain energy, which peaks at 9 carbons (around 50&nbsp;kJ&nbsp;mol<sup>&minus;1</sup>). After that, strain energy slowly decreases until 12 carbon atoms, where it drops significantly; at 14, another significant drop occurs and the strain is on a level comparable with 10&nbsp;kJ&nbsp;mol<sup>&minus;1</sup>.  At larger ring sizes there is little or no strain since there are many accessible conformations corresponding to a diamond lattice.<ref name=Dragojlovic/>

Ring strain can be considerably higher in [[bicyclic molecule|bicyclic systems]].  For example, [[bicyclobutane]], C<sub>4</sub>H<sub>6</sub>, is noted for being one of the most strained compounds that is isolatable on a large scale; its strain energy is estimated at 267&nbsp;kJ&nbsp;mol<sup>&minus;1</sup>.<!-- The source gives 63.9 kcal/mol, which equates to 267.4 kJ/mol --><ref>{{cite book|title = Advances in Alicyclic Chemistry|volume = 2|editor1-first = H.|editor1-last = Hart|editor2-first = G. J.|editor2-last = Karabatsos|year = 1968|first = K. B.|last = Wiberg|author-link = Kenneth B. Wiberg|chapter = Small Ring Bicyclo[''n''.''m''.0]alkanes|publisher = [[Academic Press]]|isbn = 9781483224213|pages = 185–254|chapter-url = https://books.google.com/books?id=9h0SBQAAQBAJ&pg=PA191}}</ref><ref>{{cite journal|first1 = K. B.|last1 = Wiberg|author-link1 = Kenneth B. Wiberg|first2 = G. M.|last2 = Lampman|first3 = R. P.|last3 = Ciula|first4 = D. S.|last4 = Connor|first5 = P.|last5 = Schertler|first6 = J.|last6 = Lavanish|title = Bicyclo[1.1.0]butane|journal = [[Tetrahedron (journal)|Tetrahedron]]|year = 1965|volume = 21|issue = 10|pages = 2749–2769|doi = 10.1016/S0040-4020(01)98361-9}}</ref>

== Reactions ==
Cycloalkanes, referred to as naphthenes, are a major substrate for the catalytic reforming process.<ref name="Ullmann">{{cite book |doi=10.1002/14356007.a18_051 |chapter=Oil Refining |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2000 |last1=Irion |first1=Walther W. |last2=Neuwirth |first2=Otto S. |isbn=3-527-30673-0 }}</ref> In the presence of a catalyst and at temperatures of about 495 to 525&nbsp;°C, naphthenes undergo [[dehydrogenation]] to give aromatic derivatives:
[[File:KatReforming1.svg|300px|center|noice]]
The process provides a way to produce high octane gasoline.

In another major industrial process, cyclohexanol is produced by the [[oxidation]] of [[cyclohexane]] in air, typically using cobalt [[catalyst]]s:<ref>Michael Tuttle Musser "Cyclohexanol and Cyclohexanone" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.</ref>
:2 C<sub>6</sub>H<sub>12</sub> + O<sub>2</sub> → 2 C<sub>6</sub>H<sub>11</sub>OH
This process coforms [[cyclohexanone]], and this mixture ("KA oil" for ketone-alcohol oil) is the main feedstock for the production of [[adipic acid]], used to make [[nylon]].

The small cycloalkanes – in particular, cyclopropane – have a lower stability due to [[Baeyer strain theory|Baeyer strain]] and [[ring strain]]. They react similarly to [[alkenes]], though they do not react in [[electrophilic addition]], but in [[nucleophilic aliphatic substitution]]. These reactions are ring-opening reactions or ring-cleavage reactions of [[alkyl cycloalkane]]s.

== Preparation ==
Many simple cycloalkanes are obtained from petroleum.  They can be produced by [[hydrogenation]] of unsaturated, even aromatic precursors.  

Numerous methods exist for preparing cycloalkanes by ring-closing reactions of difunctional precursors.  For example, diesters are cyclized in the [[Dieckmann condensation]]:
:[[File:DieckmannCondensation.png|center|290px|The Dieckmann condensation]]
The [[acyloin condensation]] can be deployed similarly. 

For larger rings ([[macrocyclization]]s) more elaborate methods are required since intramolecular ring closure competes with intermolecular reactions.
:[[File:MusconeViaRCM (cropped).svg|center]]

The [[Diels-Alder reaction]], a [4+2] cycloaddition, provides a route to cyclohexenes:
[[File:Diels-alder-stereospecificity (cropped).png|center|290px|The Dieckmann condensation]]

The corresponding [2+2] cycloaddition reactions, which usually require photochemical activation, result in cyclobutanes.

==See also==
* [[Prelog strain]]
* [[Conformational isomerism]]
* [[Alkane]]
* [[Cycloalkene]]
* [[Cycloalkyne]]

==Notes==
{{notelist}}

==References==
{{Reflist}}
*{{GoldBookRef| title=Cycloalkanes | file=C01497 | year=1995}}
*Organic Chemistry IUPAC Nomenclature. Rule A-23. Hydrogenated Compounds from Fused Polycyclic Hydrocarbons http://www.acdlabs.com/iupac/nomenclature/79/r79_73.htm
*Organic Chemistry IUPAC Nomenclature.Rule A-31. Bridged Hydrocarbons: Bicyclic Systems. http://www.acdlabs.com/iupac/nomenclature/79/r79_163.htm
*Organic Chemistry IUPAC Nomenclature.Rules A-41, A-42: Spiro Hydrocarbons http://www.acdlabs.com/iupac/nomenclature/79/r79_196.htm
*Organic Chemistry IUPAC Nomenclature.Rules A-51, A-52, A-53, A-54:Hydrocarbon Ring Assemblies http://www.acdlabs.com/iupac/nomenclature/79/r79_158.htm

==External links==
*[http://www.britannica.com/eb/article-79615/chemical-compound#615967.hook "Cycloalkanes"] at the online [[Encyclopædia Britannica]]

{{Hydrocarbons}}
{{Cycloalkanes}}

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[[Category:Cycloalkanes| ]]