Editing Alkene (section)

==Physical properties==
Many of the physical properties of alkenes and [[alkane]]s are similar: they are colorless, nonpolar, and combustible.  The [[physical state]] depends on [[molecular mass]]: like the corresponding saturated hydrocarbons, the simplest alkenes ([[ethylene]], [[propylene]], and [[butene]]) are gases at room temperature. Linear alkenes of approximately five to sixteen carbon atoms are liquids, and higher alkenes are waxy solids. The melting point of the solids also increases with increase in molecular mass.

Alkenes generally have stronger smells than their corresponding alkanes.  Ethylene has a sweet and musty odor.  Strained alkenes, in particular, like norbornene and [[Trans-Cyclooctene|''trans''-cyclooctene]] are known to have strong, unpleasant odors, a fact consistent with the stronger π complexes they form with metal ions including copper.<ref>{{Cite journal|last1=Duan|first1=Xufang|last2=Block|first2=Eric|last3=Li|first3=Zhen|last4=Connelly|first4=Timothy|last5=Zhang|first5=Jian|last6=Huang|first6=Zhimin|last7=Su|first7=Xubo|last8=Pan|first8=Yi|last9=Wu|first9=Lifang|date=2012-02-28|title=Crucial role of copper in detection of metal-coordinating odorants|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=109|issue=9|pages=3492–7|doi=10.1073/pnas.1111297109 |pmc=3295281|pmid=22328155|bibcode=2012PNAS..109.3492D|doi-access=free}}</ref>

=== Boiling and melting points ===
Below is a list of the boiling and melting points of various alkenes with the corresponding alkane and alkyne analogues.<ref name="alkene properties">{{cite web|url=https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Alkenes/Properties_of_Alkenes/Physical_Properties_of_Alkenes|title=Physical Properties of Alkenes|last1=Nguyen|first1=Trung|last2=Clark|first2=Jim|date=April 23, 2019|access-date=May 27, 2019|website=Chemistry LibreTexts}}</ref><ref>{{cite web|url=http://chemistry.elmhurst.edu/vchembook/501hcboilingpts.html|title=Boiling Points and Structures of Hydrocarbons |last=Ophardt|first=Charles|date=2003|access-date=May 27, 2019|website=Virtual Chembook}}</ref> 
{| class="wikitable"
|+Melting and boiling points in [[Celsius|°C]]
!Number of<br>carbons
!
!Alkane
!Alkene
!Alkyne
|-
|rowspan="3" |2
|Name||ethane||ethylene||acetylene
|-
|Melting point||−183||−169||−80.7
|-
|Boiling point||−89||−104||−84.7
|-
| rowspan="3" |3
|Name||propane||propylene||propyne
|-
|Melting point||−190||−185||−102.7
|-
|Boiling point||−42||−47||−23.2
|-
| rowspan="3" |4
|Name||butane||1-butene||1-butyne
|-
|Melting point||−138||−185.3||−125.7
|-
|Boiling point||−0.5||−6.2||8.0
|-
| rowspan="3" |5
|Name||pentane||1-pentene||1-pentyne
|-
|Melting point||−130||−165.2||−90.0
|-
|Boiling point||36||29.9||40.1
|}

=== Infrared spectroscopy ===
In the [[infrared|IR]] spectrum, the stretching/compression of C=C bond gives a peak at 1670–1600&nbsp;[[wave number|cm<sup>−1</sup>]].  The band is weak in symmetrical alkenes. The bending of C=C bond absorbs between 1000 and 650&nbsp;cm<sup>−1</sup> wavelength

=== NMR spectroscopy ===
In <sup>1</sup>H [[NMR]] spectroscopy, the [[hydrogen]] bonded to the carbon adjacent to double bonds will give a [[chemical shift|δ<sub>H</sub>]] of 4.5–6.5&nbsp;[[parts per million|ppm]]. The double bond will also [[Electromagnetic shielding|deshield]] the hydrogen attached to the carbons adjacent to sp<sup>2</sup> carbons, and this generates δ<sub>H</sub>=1.6–2.&nbsp;ppm peaks.<ref>{{cite web|url=http://www2.ups.edu/faculty/hanson/Spectroscopy/NMR/HNMRshift.htm|title=Overview of Chemical Shifts in H-NMR|last=Hanson|first=John|website=ups.edu|access-date=May 5, 2019}}</ref> Cis/trans isomers are distinguishable due to different [[J-coupling]] effect. Cis [[Vicinal (chemistry)|vicinal]] hydrogens will have coupling constants in the range of 6–14&nbsp;[[Hz]], whereas the trans will have coupling constants of 11–18&nbsp;Hz.<ref name="NMR of Alkenes">{{cite web|url=https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Alkenes/Properties_of_Alkenes/Nuclear_Magnetic_Resonance_(NMR)_of_Alkenes|author=<!--Not stated-->|title=Nuclear Magnetic Resonance (NMR) of Alkenes|website=Chemistry LibreTexts|date=April 23, 2019|access-date=May 5, 2019}}</ref>

In their <sup>13</sup>C NMR spectra of alkenes, double bonds also deshield the carbons, making them have low field shift. C=C double bonds usually have chemical shift of about 100–170&nbsp;ppm.<ref name="NMR of Alkenes" />

=== Combustion ===
Like most other [[hydrocarbon]]s, alkenes [[combustion|combust]] to give carbon dioxide and water.

The combustion of alkenes release less energy than burning same [[molarity]] of saturated ones with same number of carbons. 
This trend can be clearly seen in the list of [[enthalpy of combustion|standard enthalpy of combustion]] of hydrocarbons.<ref>{{cite web|url=http://www2.ucdsb.on.ca/tiss/stretton/database/organic_thermo.htm|title=Organic Compounds: Physical and Thermochemical Data|website=ucdsb.on.ca|access-date=May 5, 2019}}</ref>
{| class="wikitable"
|+Combustion energies of various hydrocarbons
!Number of<br>carbons
!Substance
!Type
!Formula
!H<sub>c</sub><sup>ø</sup><br>(kJ/mol)
|-
| rowspan="3" |2
|[[ethane]]
|saturated
|C<sub>2</sub>H<sub>6</sub>
| −1559.7
|-
|[[ethylene]]
|unsaturated
|C<sub>2</sub>H<sub>4</sub>
| −1410.8
|-
|[[acetylene]]
|unsaturated
|C<sub>2</sub>H<sub>2</sub>
| −1300.8
|-
| rowspan="3" |3
|[[propane]]
|saturated
|CH<sub>3</sub>CH<sub>2</sub>CH<sub>3</sub>
| −2219.2
|-
|[[propene]]
|unsaturated
|CH<sub>3</sub>CH=CH<sub>2</sub>
| −2058.1
|-
|[[propyne]]
|unsaturated
|CH<sub>3</sub>C≡CH
| −1938.7
|-
| rowspan="3" |4
|[[butane]]
|saturated
|CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>
| −2876.5
|-
|[[1-butene]]
|unsaturated
|CH<sub>2</sub>=CH−CH<sub>2</sub>CH<sub>3</sub>
| −2716.8
|-
|[[1-butyne]]
|unsaturated
|CH≡C-CH<sub>2</sub>CH<sub>3</sub>
| −2596.6
|}