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{{short description|Covalent compound that contains two double bonds}}
{{short description|Covalent compound that contains two double bonds}}
{{About|organic chemicals|the surname "Diene" used in West Africa|Serer people}}
{{About|organic chemicals|the surname "Diene" used in West Africa|Serer people|and|Diène}}


[[File:1,3-butadiene.svg|thumb|150px|[[1,3-Butadiene|1,3-butadiene]]]]
[[File:1,3-butadiene.svg|thumb|150px|[[1,3-Butadiene|1,3-butadiene]]]]


In [[organic chemistry]], a '''diene''' ({{IPAc-en|ˈ|d|aɪ|iː|n}} {{respell|DY|een}}); also '''diolefin''', {{IPAc-en|d|aɪ|ˈ|oʊ|l|ə|f|ᵻ|n}} {{respell|dy|OH|lə|fin}}) or '''alkadiene''') is a [[covalent compound]] that contains two [[double bond]]s, usually among [[carbon]] atoms.<ref name="IUPAC dienes">{{GoldBookRef|file=D01699|title=dienes}}</ref> They thus contain two [[alkene|alk''ene'']] units, with the standard prefix ''di'' of [[systematic nomenclature]].  As a subunit of more complex molecules, dienes occur in naturally occurring and synthetic chemicals and are used in [[organic synthesis]].  [[Conjugated system|Conjugated]] dienes are widely used as [[monomer]]s in the [[polymer]] industry. [[Polyunsaturated fat]]s are of interest to [[nutrition]].
In [[organic chemistry]], a '''diene''' ({{IPAc-en|ˈ|d|aɪ|iː|n}} {{respell|DY|een}}); also '''diolefin''', {{IPAc-en|d|aɪ|ˈ|oʊ|l|ə|f|ᵻ|n}} {{respell|dy|OH|lə|fin}}) or '''alkadiene''') is a [[covalent compound]] that contains two [[double bond]]s, usually among [[carbon]] atoms.<ref name="IUPAC dienes">{{GoldBookRef|file=D01699|title=dienes}}</ref> They thus contain two [[alkene|alk''ene'']] units, with the standard prefix ''di'' of [[systematic nomenclature]].  As a subunit of more complex molecules, dienes occur in naturally occurring and synthetic chemicals and are used in [[organic synthesis]].  [[Conjugated system|Conjugated]] dienes are widely used as [[monomer]]s in the [[polymer]] industry. [[Polyunsaturated fat]]s are of interest to [[nutrition]]. According to the ''[[Gold Book]]'' definition, a "diene" could include one or more [[heteroatom]]s which replace unsaturated carbon atoms, giving structures that could more specifically be called ''heterodienes''.<ref name="IUPAC dienes"/>


==Classes==
Compounds that contain more than two double bonds are called [[polyene]]s. Polyenes and dienes share many properties.
 
==Classification==
Dienes can be divided into three classes, depending on the relative location of the double bonds:<ref name="IUPAC dienes"/>
Dienes can be divided into three classes, depending on the relative location of the double bonds:<ref name="IUPAC dienes"/>
#'''Cumulated dienes''' have the double bonds sharing a common atom. The result is more specifically called an [[allene]].
#'''Cumulated dienes''' have the double bonds sharing a common atom. The result is more specifically called an [[allene]].
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[[File:Dienes various examples.png|thumb|center|650px|alt=Structure of various alkadienes (also called dienes or diolefins)|Some dienes: '''A''': 1,2-Propadiene, also known as [[allene]], is the simplest cumulated diene. '''B''': [[Isoprene]], also known as 2-methyl-1,3-butadiene, the precursor to natural rubber. '''C''': [[1,3-Butadiene]], a  precursor to synthetic polymers.  '''D''': [[1,5-Cyclooctadiene]], an unconjugated diene (notice that each double bond is two carbons away from the other). '''E''': [[Norbornadiene]], a strained bicyclic and unconjugated  diene.  '''F''': [[Dicyclopentadiene]].]]
[[File:Dienes various examples.png|thumb|center|650px|alt=Structure of various alkadienes (also called dienes or diolefins)|Some dienes: '''A''': 1,2-Propadiene, also known as [[allene]], is the simplest cumulated diene. '''B''': [[Isoprene]], also known as 2-methyl-1,3-butadiene, the precursor to natural rubber. '''C''': [[1,3-Butadiene]], a  precursor to synthetic polymers.  '''D''': [[1,5-Cyclooctadiene]], an unconjugated diene (notice that each double bond is two carbons away from the other). '''E''': [[Norbornadiene]], a strained bicyclic and unconjugated  diene.  '''F''': [[Dicyclopentadiene]].]]


According to the ''[[Gold Book]]'' definition, a "diene" could include one or more [[heteroatom]]s which replace unsaturated carbon atoms, giving structures that could more specifically be called ''heterodienes''.<ref name="IUPAC dienes"/>
==Conjugated dienes==
Conjugated dienes are also called 1,3-dienes. Commercially significant conjugated dienes include 1,3-butadiene, [[isoprene]], [[chloroprene]], and [[cyclopentadiene]].  Other common members are [[1,3-Pentadiene|1,3-pentadiene]] (piperylene) and [[1,3-Cyclohexadiene|1,3-cyclohexadiene]].  


Compounds that contain more than two double bonds are called [[polyene]]s. Polyenes and dienes share many properties.
On an industrial scale, butadiene and pentadiene are prepared by [[steam cracking]]. In a similar process, [[dicyclopentadiene]] is obtained from [[coal tar]]s.  Conjugated dienes can be formed by the addition of two good leaving groups across a double bond, followed by base workup.<ref>Not exactly on point, but see: {{OrgSynth|author1=Block |first1=E.|author2= Aslam |first2=M.|title=A General Synthetic Method for the Preparation of Conjugated Dienes from Olefins using Bromomethanesulfonyl Bromide: 1,2-Dimethylenecyclohexane|collvol=Coll. Vol. 8|collvolpages=212 |prep=cv8p0212 |year=1993}}</ref>{{better cite needed|date=January 2026}}  Dienes can also be produced from the [[semihydrogenation]] of diynes. Pd catalysts tend to degrade homoconjugate dienes, but Ni works well.<ref>{{cite news|url=https://www.organic-chemistry.org/Highlights/2018/05February.shtm|date=February 5, 2018|first=Douglass&nbsp;F.|last=Taber|title=The Sato/Chida synthesis of madangamine A|magazine=Organic Chemistry Highlights}}</ref> Myriad [[name reaction]]s have been developed, including the [[Whiting reaction]].


==Synthesis of dienes==
===Reactions===
The most heavily practiced reaction of dienes is [[polymerization]] to [[Synthetic rubber|rubber]] used in tires and other flexible objects.  These reactions require metal catalysts such as those used in [[Ziegler-Natta polymerization]].<ref>{{cite journal |last1=Ricci |first1=Giovanni |last2=Pampaloni |first2=Guido |last3=Sommazzi |first3=Anna |last4=Masi |first4=Francesco |title=Dienes Polymerization: Where We Are and What Lies Ahead |journal=Macromolecules |date=2021 |volume=54 |issue=13 |pages=5879–5914 |doi=10.1021/acs.macromol.1c00004}}</ref>


On an industrial scale, butadiene is prepared by [[thermal cracking]] of [[butane]]s. In a similarly non-selective process, [[dicyclopentadiene]] is obtained from [[coal tar]]s.
An important reaction for conjugated dienes is the [[Diels–Alder reaction]].  Many specialized dienes have been developed to exploit this reactivity for the synthesis of [[natural product]]s (e.g., [[Danishefsky's diene]]).  


In the laboratory, more directed and more delicate processes are employed such as [[dehydrohalogenation]]s and [[Condensation (chemistry)|condensations]].  Myriad [[organic reaction|methods]] have been developed, such as the [[Whiting reaction]].  Families of nonconjugated dienes are derived from the [[oligomerization]] and [[Dimer (chemistry)|dimerization]] of conjugated dienes.  For example, 1,5-cyclooctadiene and 4-vinylcyclohexene are produced by dimerization of [[1,3-Butadiene|1,3-butadiene]].
Conjugated dienes add reagents such as [[bromine]] and [[hydrogen]] by both 1,2-addition and 1,4-addition pathways.
 
Diene-containing [[fatty acid]]s are [[biosynthesis|biosynthesized]] from [[acetyl CoA]].


==Nonconjugated dienes==
α,ω-Dienes have the formula (CH<sub>2</sub>)<sub>n</sub>(CH=CH<sub>2</sub>)<sub>2</sub>.  They are prepared industrially by [[ethenolysis]] of cyclic dienes.  For example, [[1,5-Hexadiene|1,5-hexadiene]] and 1,9-decadiene, useful crosslinking agents and synthetic intermediates, are produced from [[1,5-Cyclooctadiene|1,5-cyclooctadiene]] and [[cyclooctene]], respectively.  The catalyst is derived from Re<sub>2</sub>O<sub>7</sub> on alumina.<ref name=KO>{{cite encyclopedia|title=Metathesis|encyclopedia=Kirk-Othmer Encyclopedia of Chemical Technology|author=Lionel Delaude |author2=Alfred F. Noels |year=2005| doi=10.1002/0471238961.metanoel.a01|place=Weinheim|publisher=Wiley-VCH|isbn=0-471-23896-1}}</ref>
α,ω-Dienes have the formula (CH<sub>2</sub>)<sub>n</sub>(CH=CH<sub>2</sub>)<sub>2</sub>.  They are prepared industrially by [[ethenolysis]] of cyclic dienes.  For example, [[1,5-Hexadiene|1,5-hexadiene]] and 1,9-decadiene, useful crosslinking agents and synthetic intermediates, are produced from [[1,5-Cyclooctadiene|1,5-cyclooctadiene]] and [[cyclooctene]], respectively.  The catalyst is derived from Re<sub>2</sub>O<sub>7</sub> on alumina.<ref name=KO>{{cite encyclopedia|title=Metathesis|encyclopedia=Kirk-Othmer Encyclopedia of Chemical Technology|author=Lionel Delaude |author2=Alfred F. Noels |year=2005| doi=10.1002/0471238961.metanoel.a01|place=Weinheim|publisher=Wiley-VCH|isbn=0-471-23896-1}}</ref>
Families of nonconjugated dienes are derived from the [[oligomerization]] and [[Dimer (chemistry)|dimerization]] of conjugated dienes.  For example, 1,5-cyclooctadiene and 4-vinylcyclohexene are produced by dimerization of [[1,3-Butadiene|1,3-butadiene]].


== Reactivity and uses==
Nonconjugated dienes are substrates for [[ring-closing metathesis]] reactions.  These reactions require a metal [[catalyst]]:
::[[File:RCM cyclophane example.png|520px]]


===Polymerization===
Addition of polar reagents can generate complex architectures:<ref>{{OrgSynth | author = Roger Bishop | collvol = 9 | collvolpages = 692 | prep = CV9P0692
The most heavily practiced reaction of alkenes, dienes included, is [[polymerization]].  1,3-Butadiene is a precursor to [[Synthetic rubber|rubber]] used in tires, and [[isoprene]] is the precursor to [[natural rubber]].  [[Chloroprene]] is related but it is a synthetic monomer.
 
===Cycloadditions===
An important reaction for conjugated dienes is the [[Diels–Alder reaction]].  Many specialized dienes have been developed to exploit this reactivity for the synthesis of [[natural product]]s (e.g., [[Danishefsky's diene]]).
 
===Other addition reactions===
Conjugated dienes add reagents such as [[bromine]] and [[hydrogen]] by both 1,2-addition and 1,4-addition pathways.  Addition of polar reagents can generate complex architectures:<ref>{{OrgSynth | author = Roger Bishop | collvol = 9 | collvolpages = 692 | prep = CV9P0692
| title =9-Thiabicyclo[3.3.1]nonane-2,6-dione}}{{cite journal | title =2,6-Dichloro-9-thiabicyclo[3.3.1]nonane: Multigram Display of Azide and Cyanide Components on a Versatile Scaffold | first4 = M. G. | last4 = Finn | first3 = K. Barry | last3 = Sharpless | journal = [[Molecules (journal)|Molecules]] | first2 = Antonella | year = 2006 | volume = 11 | last2 = Converso | pages = 212–218 | doi = 10.3390/11040212 | author = Díaz, David Díaz | issue = 4| pmid = 17962753 | pmc = 6148556 | doi-access = free }}</ref>
| title =9-Thiabicyclo[3.3.1]nonane-2,6-dione}}{{cite journal | title =2,6-Dichloro-9-thiabicyclo[3.3.1]nonane: Multigram Display of Azide and Cyanide Components on a Versatile Scaffold | first4 = M. G. | last4 = Finn | first3 = K. Barry | last3 = Sharpless | journal = [[Molecules (journal)|Molecules]] | first2 = Antonella | year = 2006 | volume = 11 | last2 = Converso | pages = 212–218 | doi = 10.3390/11040212 | author = Díaz, David Díaz | issue = 4| pmid = 17962753 | pmc = 6148556 | doi-access = free }}</ref>
::[[Image:CODSCl2.png|450px|2,6-Dichloro-9-thiabicyclo[3.3.1]nonane, synthesis and reactions]]
::[[Image:CODSCl2.png|450px|2,6-Dichloro-9-thiabicyclo[3.3.1]nonane, synthesis and reactions]]


===Metathesis reactions===
==Biological dienes==
Nonconjugated dienes are substrates for [[ring-closing metathesis]] reactions.  These reactions require a metal [[catalyst]]:
[[image:LAnumbering.png|thumb|right|Linoleic acid|240px]]
::[[File:RCM cyclophane example.png|520px]]
Diene-containing [[fatty acid]]s are common.  Common ones are [[linolenic acid]] {{chem2|CH3CH2CH\dCHCH2CH\dCHCH2CH\dCH(CH2)7CO2H}} and [[linoleic acid]] {{chem2|CH3(CH2)4CH\dCHCH2CH\dCH(CH2)7CO2H}}.  The 1,3-pentadiene group in these 1,4-dienes is susceptible to H-atom abstraction. The derived fats ([[triglyceride]]s) are [[drying oil]]s


===Acidity===
==Acidity==
The position adjacent to a double bond is [[acid]]ic because the resulting [[allyl]] anion is stabilized by resonance. This effect becomes more pronounced as more alkenes are involved to create greater stability. For example, deprotonation at position 3 of a 1,4-diene or position 5 of a 1,3-diene give a [[pentadienyl]] anion. An even greater effect is seen if the anion is aromatic, for example, deprotonation of [[cyclopentadiene]] to give the [[cyclopentadienyl anion]].<!-- TODO: chart of pKa for methylene in alkane, singly and doubly allylic, and Cp -->
The position adjacent to a double bond is [[acid]]ic because the resulting [[allyl]] anion is stabilized by resonance. This effect becomes more pronounced as more alkenes are involved to create greater stability. For example, deprotonation at position 3 of a 1,4-diene or position 5 of a 1,3-diene give a [[pentadienyl]] anion. An even greater effect is seen if the anion is aromatic, for example, deprotonation of [[cyclopentadiene]] to give the [[cyclopentadienyl anion]].<!-- TODO: chart of pKa for methylene in alkane, singly and doubly allylic, and Cp -->


[[File:HayashiChiralNBD.svg|thumb|left|122px|[[C2-Symmetric ligands|C<sub>2</sub>-symmetric]] diene ligand used in [[asymmetric catalysis]].<ref>{{cite journal|vauthors=Hayashi T, Ueyama K, Tokunaga N, Yoshida K|title=A Chiral Chelating Diene as a New Type of Chiral Ligand for Transition Metal Catalysts: Its Preparation and Use for the Rhodium-Catalyzed Asymmetric 1,4-Addition|journal=J. Am. Chem. Soc.|year=2003|volume=125|issue=38|pages=11508–11509|doi=10.1021/ja037367z|pmid=13129348}}</ref>]]
[[File:HayashiChiralNBD.svg|thumb|left|122px|[[C2-Symmetric ligands|C<sub>2</sub>-symmetric]] diene ligand used in [[asymmetric catalysis]].<ref>{{cite journal|vauthors=Hayashi T, Ueyama K, Tokunaga N, Yoshida K|title=A Chiral Chelating Diene as a New Type of Chiral Ligand for Transition Metal Catalysts: Its Preparation and Use for the Rhodium-Catalyzed Asymmetric 1,4-Addition|journal=J. Am. Chem. Soc.|year=2003|volume=125|issue=38|pages=11508–11509|doi=10.1021/ja037367z|pmid=13129348 |bibcode=2003JAChS.12511508H }}</ref>]]


===As ligands===
===As ligands===

Latest revision as of 21:52, 18 May 2026

This article is about organic chemicals. For the surname "Diene" used in West Africa, see Serer people and Diène.
File:1,3-butadiene.svg
1,3-butadiene

In organic chemistry, a diene (/ˈdaɪiːn/ DY-een); also diolefin, /daɪˈoʊləfɪn/ dy-OH-lə-fin) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms.[1] They thus contain two alkene units, with the standard prefix di of systematic nomenclature. As a subunit of more complex molecules, dienes occur in naturally occurring and synthetic chemicals and are used in organic synthesis. Conjugated dienes are widely used as monomers in the polymer industry. Polyunsaturated fats are of interest to nutrition. According to the Gold Book definition, a "diene" could include one or more heteroatoms which replace unsaturated carbon atoms, giving structures that could more specifically be called heterodienes.[1]

Compounds that contain more than two double bonds are called polyenes. Polyenes and dienes share many properties.

Classification

Dienes can be divided into three classes, depending on the relative location of the double bonds:[1]

  1. Cumulated dienes have the double bonds sharing a common atom. The result is more specifically called an allene.
  2. Conjugated dienes have conjugated double bonds separated by one single bond. Conjugated dienes are more stable than other dienes because of resonance.
  3. Unconjugated dienes have the double bonds separated by two or more single bonds. They are usually less stable than isomeric conjugated dienes. This can also be known as an isolated diene.
Structure of various alkadienes (also called dienes or diolefins)
Some dienes: A: 1,2-Propadiene, also known as allene, is the simplest cumulated diene. B: Isoprene, also known as 2-methyl-1,3-butadiene, the precursor to natural rubber. C: 1,3-Butadiene, a precursor to synthetic polymers. D: 1,5-Cyclooctadiene, an unconjugated diene (notice that each double bond is two carbons away from the other). E: Norbornadiene, a strained bicyclic and unconjugated diene. F: Dicyclopentadiene.

Conjugated dienes

Conjugated dienes are also called 1,3-dienes. Commercially significant conjugated dienes include 1,3-butadiene, isoprene, chloroprene, and cyclopentadiene. Other common members are 1,3-pentadiene (piperylene) and 1,3-cyclohexadiene.

On an industrial scale, butadiene and pentadiene are prepared by steam cracking. In a similar process, dicyclopentadiene is obtained from coal tars. Conjugated dienes can be formed by the addition of two good leaving groups across a double bond, followed by base workup.[2]Template:Better cite needed Dienes can also be produced from the semihydrogenation of diynes. Pd catalysts tend to degrade homoconjugate dienes, but Ni works well.[3] Myriad name reactions have been developed, including the Whiting reaction.

Reactions

The most heavily practiced reaction of dienes is polymerization to rubber used in tires and other flexible objects. These reactions require metal catalysts such as those used in Ziegler-Natta polymerization.[4]

An important reaction for conjugated dienes is the Diels–Alder reaction. Many specialized dienes have been developed to exploit this reactivity for the synthesis of natural products (e.g., Danishefsky's diene).

Conjugated dienes add reagents such as bromine and hydrogen by both 1,2-addition and 1,4-addition pathways.

Nonconjugated dienes

α,ω-Dienes have the formula (CH2)n(CH=CH2)2. They are prepared industrially by ethenolysis of cyclic dienes. For example, 1,5-hexadiene and 1,9-decadiene, useful crosslinking agents and synthetic intermediates, are produced from 1,5-cyclooctadiene and cyclooctene, respectively. The catalyst is derived from Re2O7 on alumina.[5] Families of nonconjugated dienes are derived from the oligomerization and dimerization of conjugated dienes. For example, 1,5-cyclooctadiene and 4-vinylcyclohexene are produced by dimerization of 1,3-butadiene.

Nonconjugated dienes are substrates for ring-closing metathesis reactions. These reactions require a metal catalyst:

File:RCM cyclophane example.png

Addition of polar reagents can generate complex architectures:[6]

2,6-Dichloro-9-thiabicyclo[3.3.1]nonane, synthesis and reactions

Biological dienes

File:LAnumbering.png
Linoleic acid

Diene-containing fatty acids are common. Common ones are linolenic acid CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7CO2H and linoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7CO2H. The 1,3-pentadiene group in these 1,4-dienes is susceptible to H-atom abstraction. The derived fats (triglycerides) are drying oils

Acidity

The position adjacent to a double bond is acidic because the resulting allyl anion is stabilized by resonance. This effect becomes more pronounced as more alkenes are involved to create greater stability. For example, deprotonation at position 3 of a 1,4-diene or position 5 of a 1,3-diene give a pentadienyl anion. An even greater effect is seen if the anion is aromatic, for example, deprotonation of cyclopentadiene to give the cyclopentadienyl anion.

File:HayashiChiralNBD.svg
C2-symmetric diene ligand used in asymmetric catalysis.[7]

As ligands

Dienes are widely used chelating ligands in organometallic chemistry. In some cases they serve as placeholder ligands, being removed during a catalytic cycle. For example, the cyclooctadiene ("cod") ligands in bis(cyclooctadiene)nickel(0) are labile. In some cases, dienes are spectator ligands, remaining coordinated throughout a catalytic cycle and influencing the product distributions. Chiral dienes have also been described.[8] Other diene complexes include (butadiene)iron tricarbonyl, cyclobutadieneiron tricarbonyl, and cyclooctadiene rhodium chloride dimer.

References

  1. ↑ 1.0 1.1 1.2 Template:GoldBookRef
  2. ↑ Not exactly on point, but see: Template:OrgSynth
  3. ↑ Taber, Douglass F. (February 5, 2018). "The Sato/Chida synthesis of madangamine A". Organic Chemistry Highlights.
  4. ↑ Ricci, Giovanni; Pampaloni, Guido; Sommazzi, Anna; Masi, Francesco (2021). "Dienes Polymerization: Where We Are and What Lies Ahead". Macromolecules. 54 (13): 5879–5914. doi:10.1021/acs.macromol.1c00004.
  5. ↑ Lionel Delaude; Alfred F. Noels (2005). "Metathesis". Kirk-Othmer Encyclopedia of Chemical Technology. Weinheim: Wiley-VCH. doi:10.1002/0471238961.metanoel.a01. ISBN 0-471-23896-1.
  6. ↑ Template:OrgSynthDíaz, David Díaz; Converso, Antonella; Sharpless, K. Barry; Finn, M. G. (2006). "2,6-Dichloro-9-thiabicyclo[3.3.1]nonane: Multigram Display of Azide and Cyanide Components on a Versatile Scaffold". Molecules. 11 (4): 212–218. doi:10.3390/11040212. PMC 6148556. PMID 17962753.
  7. ↑ Hayashi T, Ueyama K, Tokunaga N, Yoshida K (2003). "A Chiral Chelating Diene as a New Type of Chiral Ligand for Transition Metal Catalysts: Its Preparation and Use for the Rhodium-Catalyzed Asymmetric 1,4-Addition". J. Am. Chem. Soc. 125 (38): 11508–11509. Bibcode:2003JAChS.12511508H. doi:10.1021/ja037367z. PMID 13129348.
  8. ↑ Huang, Yinhua; Hayashi, Tamio (2022-09-28). "Chiral Diene Ligands in Asymmetric Catalysis". Chemical Reviews. 122 (18): 14346–14404. doi:10.1021/acs.chemrev.2c00218. ISSN 0009-2665. PMID 35972018 Check |pmid= value (help).

Template:Hydrocarbons

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