Double bond

<h2 id="double-bonds-in-alkenes">Double bonds in alkenes</h2>

<p>The type of bonding can be explained in terms of <a href="/facts/Orbital_hybridisation/Fl7sz8Jm">orbital hybridisation</a>. In <a href="/facts/Ethylene/QMNBYLYn">ethylene</a> each carbon atom has three <a href="/facts/Orbital_hybridization/Fl7sz8Jm">sp2</a> orbitals and one <a href="/facts/Atomic_orbital/tKhgl6mL">p-orbital</a>. The three sp2 orbitals lie in a plane with ~120° angles. The p-orbital is perpendicular to this plane. When the carbon atoms approach each other, two of the sp2 orbitals overlap to form a <a href="/facts/Sigma_bond/CSyEe5CY">sigma bond</a>. At the same time, the two p-orbitals approach (again in the same plane) and together they form a <a href="/facts/Pi_bond/3Q6LAGYK">pi bond</a>. For maximum overlap, the p-orbitals have to remain parallel, and, therefore, rotation around the central bond is not possible. This property gives rise to <a href="/facts/Cis-trans_isomerism/vqlchJly">cis-trans isomerism</a>. Double bonds are shorter than single bonds because p-orbital overlap is maximized.
</p>

<p>With 133 pm, the ethylene <a href="/facts/Carbon%25E2%2580%2593carbon_bond/nLE4z5BK">C=C</a> <a href="/facts/Bond_length/rHHIBH6q">bond length</a> is shorter than the C−C length in <a href="/facts/Ethane/BGCzc6yh">ethane</a> with 154 pm. The double bond is also stronger, 636 <a href="/facts/Joule/9ndq9jD2">kJ</a> <a href="/facts/Mole_(unit)/kCMFwCc0">mol</a>−1 versus 368 kJ mol−1 but not twice as much as the pi-bond is weaker than the sigma bond due to less effective pi-overlap.
</p><p>In an alternative representation, the double bond results from two overlapping sp3 orbitals as in a <a href="/facts/Bent_bond/NQ7odhFQ">bent bond</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p>
<h2 id="variations">Variations</h2>
<p>In molecules with alternating double bonds and single bonds, p-orbital overlap can exist over multiple atoms in a chain, giving rise to a <a href="/facts/Conjugated_system/Ddx9qzox">conjugated system</a>. Conjugation can be found in systems such as <a href="/facts/Diene/F5NxrLPW">dienes</a> and <a href="/facts/Alpha-beta_Unsaturated_carbonyl_compounds/gAflh5z4">enones</a>. In <a href="/facts/Cyclic_compound/TH2ReKIQ">cyclic molecules</a>, conjugation can lead to <a href="/facts/Aromaticity/wK0DzRY6">aromaticity</a>. In <a href="/facts/Cumulene/UtxYSvxN">cumulenes</a>, two double bonds are adjacent and do not overlap with each other.
</p><p>Double bonds are common for <a href="/facts/Period_2_element/1ajRWfrb">period 2 elements</a> <a href="/facts/Carbon/ukrgQexo">carbon</a>, <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a>, and <a href="/facts/Oxygen/acyn6o8r">oxygen</a>, and less common with elements of higher periods, a distinction called the <i><a href="/facts/Double_bond_rule/kxtnRvH8">double bond rule</a></i>. Metals, too, can engage in multiple bonding in a <a href="/facts/Metal%25E2%2580%2593ligand_multiple_bond/danJJQu8">metal–ligand multiple bond</a>.
</p>
<h2 id="group-14-alkene-homologs">Group 14 alkene homologs</h2>
<p>Double bonded compounds, <a href="/facts/Alkene/RtYcS6kU">alkene</a> homologs, R2E=ER2 are now known for all of the heavier <a href="/facts/Carbon_group/PkWCV3Vx">group 14</a> elements. Unlike the alkenes these compounds are not planar but adopt twisted and/or trans bent structures. These effects become more pronounced for the heavier elements. The distannene (Me3Si)2CHSn=SnCH(SiMe3)2 has a tin-tin bond length just a little shorter than a single bond, a trans bent structure with pyramidal coordination at each tin atom, and readily dissociates in solution to form (Me3Si)2CHSn: (stannanediyl, a carbene analog). The bonding comprises two weak donor acceptor bonds, the lone pair on each tin atom overlapping with the empty p orbital on the other.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>  In contrast, in disilenes each silicon atom has planar coordination but the substituents are twisted so that the molecule as a whole is not planar. In diplumbenes the Pb=Pb bond length can be longer than that of many corresponding single bonds<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> Plumbenes and stannenes generally dissociate in solution into monomers with bond enthalpies that are just a fraction of the corresponding single bonds. Some double bonds plumbenes and stannenes are similar in strength to hydrogen bonds.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The <a href="/facts/Carter%25E2%2580%2593Goddard%25E2%2580%2593Malrieu%25E2%2580%2593Trinquier_model/cA85rGbv">Carter–Goddard–Malrieu–Trinquier model</a> can be used to predict the nature of the bonding.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>
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<h2 id="types-of-double-bonds-between-atoms">Types of double bonds between atoms</h2>
<table><tbody><tr><th></th><th>C</th><th>O</th><th>N</th><th>S</th><th>Si</th><th>Ge</th><th>Sn</th><th>Pb</th></tr><tr><th>C</th><td><a href="/facts/Alkene/RtYcS6kU">alkene</a></td><td><a href="/facts/Carbonyl/KJ71bo3X">carbonyl group</a></td><td><a href="/facts/Imine/yK72z07j">imine</a></td><td><a href="/facts/Thioketone/wMf09spv">thioketone</a>, <a href="/facts/Thial/PdqABLbb">thial</a></td><td><a href="/facts/Organosilicon/JvUwzDQ4">alkylidenesilanes</a></td><td></td><td></td><td></td></tr><tr><th>O</th><td></td><td><a href="/facts/Oxygen/acyn6o8r">dioxygen</a></td><td><a href="/facts/Nitroso/Irref1C6">nitroso compound</a></td><td><a href="/facts/Sulfoxide/Stk3Vnj9">sulfoxide</a>, <a href="/facts/Sulfone/LJLP1RcT">sulfone</a>, <a href="/facts/Sulfinic_acid/Ur6P5qNX">sulfinic acid</a>, <a href="/facts/Sulfonic_acid/6JHPGnNY">sulfonic acid</a></td><td></td><td></td><td></td><td></td></tr><tr><th>N</th><td></td><td></td><td><a href="/facts/Azo_compound/dnl1WKnK">azo compound</a></td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>S</th><td></td><td></td><td></td><td><a href="/facts/Disulfur/otzhNhox">disulfur</a></td><td></td><td></td><td></td><td></td></tr><tr><th>Si</th><td></td><td></td><td></td><td></td><td><a href="/facts/Silenes/mSr8aF2N">silenes</a></td><td></td><td></td><td></td></tr><tr><th>Ge</th><td></td><td></td><td></td><td></td><td></td><td>germenes</td><td></td><td></td></tr><tr><th>Sn</th><td></td><td></td><td></td><td></td><td></td><td></td><td>stannenes</td><td></td></tr><tr><th>Pb</th><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>plumbenes</td></tr></tbody></table>

<ul><li>Pyykkö, Pekka; Riedel, Sebastian; Patzschke, Michael (2005). "Triple-Bond Covalent Radii". <i>Chemistry: A European Journal</i>. 11 (12): 3511–20. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1002%2Fchem.200401299">10.1002/chem.200401299</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/15832398">15832398</a>.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>March, Jerry, 1929-1997. (1985). Advanced organic chemistry : reactions, mechanisms, and structure (3rd ed.). New York: Wiley. ISBN 0-471-88841-9. OCLC 10998226. Archived from the original on 2019-12-10. Retrieved 2020-12-12.{{cite book}}:  CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) <a href="0-471-88841-9" target="_blank">0-471-88841-9</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>McMurry, John. Organic chemistry (Ninth ed.). Boston, MA, USA. ISBN 978-1-305-08048-5. OCLC 907259297. Archived from the original on 2024-04-04. Retrieved 2020-12-12. <a href="978-1-305-08048-5" target="_blank">978-1-305-08048-5</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Carey, Francis A., 1937- (2007). Advanced organic chemistry. Sundberg, Richard J., 1938- (5th ed.). New York: Springer. ISBN 978-0-387-44897-8. OCLC 154040953. Archived from the original on 2024-04-04. Retrieved 2020-12-12.{{cite book}}:  CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) <a href="978-0-387-44897-8" target="_blank">978-0-387-44897-8</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Power, Philip P. (1999). "π-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements". Chemical Reviews. 99 (12): 3463–3504. doi:10.1021/cr9408989. PMID 11849028. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Wang, Yuzhong; Robinson, Gregory H. (2009). "Unique homonuclear multiple bonding in main group compounds". Chemical Communications (35). Royal Society of Chemistry: 5201–5213. doi:10.1039/B908048A. PMID 19707626. <a href="/wiki/Royal_Society_of_Chemistry" target="_blank">/wiki/Royal_Society_of_Chemistry</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Wang, Yuzhong; Robinson, Gregory H. (2009). "Unique homonuclear multiple bonding in main group compounds". Chemical Communications (35). Royal Society of Chemistry: 5201–5213. doi:10.1039/B908048A. PMID 19707626. <a href="/wiki/Royal_Society_of_Chemistry" target="_blank">/wiki/Royal_Society_of_Chemistry</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Power, Philip P. (1999). "π-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements". Chemical Reviews. 99 (12): 3463–3504. doi:10.1021/cr9408989. PMID 11849028. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>Power, Philip P. (1999). "π-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements". Chemical Reviews. 99 (12): 3463–3504. doi:10.1021/cr9408989. PMID 11849028. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
</ol>

Double bond open-in-new

Double bond