Editing Allyl group (section)

==Bonding==
The allyl group is widely encountered in organic chemistry.<ref name=March>Jerry March, "Advanced Organic Chemistry" 4th Ed.  J. Wiley and Sons, 1992: New York.  {{ISBN|0-471-60180-2}}.</ref> Allylic [[free radical|radicals]], [[Carbanion|anions]], and [[Carbocation|cations]] are often discussed as [[Reactive intermediate|intermediates in reactions]].  All feature three contiguous sp²-hybridized carbon centers and all derive stability from resonance.<ref name=McMurry>Organic Chemistry John McMurry 2nd ed. 1988</ref> Each species can be presented by two [[resonance structures]] with the charge or unpaired electron distributed at both 1,3 positions.

:[[File:Allyl anion.svg|thumb|none|320px|[[Resonance (chemistry)|Resonance structure]] of the allyl anion.  The cation is identical, but carries an opposite-sign charge.<ref>{{cite book|pages=56–57|chapter=The properties of alkene carbonium ions and carbanions|first=Herman&nbsp;G.|last=Richey|title=The Chemistry of Alkenes|volume=2|series=The Chemistry of Functional Groups|editor-first=Jacob|editor-last=Zabicky|year=1970|publisher=Interscience / William Clowes&nbsp;& Sons|location=London|lccn=64-25218|isbn=0471980501}}</ref>]]

In terms of [[MO theory]], the [[MO diagram]] has three molecular orbitals: the first one bonding, the second one non-bonding, and the higher energy orbital is antibonding.<ref name=boyd>{{cite book|title = Organic Chemistry |edition = 4th |last1= Morrison|first1 = Robert Thornton|last2= Boyd|first2= Robert Neilson|date =  1987|publisher = Allyn and Bacon}}</ref>

:[[File:AllylMO.png|thumb|none|200 px|MO diagram for allyl π orbitals.  In the radical (shown), the intermediate Ψ<sub>2</sub> orbital is singly occupied; in the cation, unoccupied; and in the anion, full.]]

<ref>{{cite journal |doi=10.1021/acs.chemrev.0c00157|title=Carbon–Carbon Bond Cleavage at Allylic Positions: Retro-allylation and Deallylation |year=2021 |last1=Nogi |first1=Keisuke |last2=Yorimitsu |first2=Hideki |journal=Chemical Reviews |volume=121 |issue=1 |pages=345–364 |pmid=32396335 |s2cid=218617434 }}</ref>