Editing Alkene (section)

===Shape===
As predicted by the [[VSEPR theory|VSEPR]] model of [[electron]] pair repulsion, the [[molecular geometry]] of alkenes includes [[bond angle]]s about each carbon atom in a double bond of about 120°. The angle may vary because of [[steric strain]] introduced by [[nonbonded interactions]] between [[functional group]]s attached to the carbon atoms of the double bond. For example, the C–C–C bond angle in [[propylene]] is 123.9°.

For bridged alkenes, [[Bredt's rule]] states that a double bond cannot occur at the bridgehead of a bridged ring system unless the rings are large enough.<ref name=Bansal /> Following Fawcett and defining ''S'' as the total number of non-bridgehead atoms in the rings,<ref>{{cite journal |title=Bredt's Rule of Double Bonds in Atomic-Bridged-Ring Structures |first=Frank S. |last=Fawcett |journal=[[Chem. Rev.]] |year=1950 |volume=47 |issue=2 |pages=219–274 |doi=10.1021/cr60147a003 |pmid=24538877}}</ref> bicyclic systems require ''S''&nbsp;≥&nbsp;7 for stability<ref name=Bansal>{{cite book |title=Organic Reaction Mechanisms |chapter=Bredt's Rule |pages=14–16 |first=Raj K. |last=Bansal |edition=3rd |year=1998 |publisher=[[McGraw-Hill Education]] |isbn=978-0-07-462083-0 |chapter-url=https://books.google.com/books?id=bga3xjLVCo0C&pg=PT29}}</ref> and tricyclic systems require ''S''&nbsp;≥&nbsp;11.<ref>{{Cite book |year=2010 |chapter=Bredt's Rule |title=Comprehensive Organic Name Reactions and Reagents |volume=116 |pages=525–8 |doi=10.1002/9780470638859.conrr116 |isbn=978-0-470-63885-9}}</ref>