Do Double Bonds Flip? Does Electron Density Move?

[caption id="attachment_7788" align="alignright" width="440"] 1,3,5 Hexatriene - NIST Image[/caption] How do double bonds flip, and what is the significance? The shorthand drawing of a double bond looks like an equal sign between two atoms. The double bond between the two carbon atoms of ethene gas, H₂C=CH₂, well illustrates this. Some organic compounds possess conjugated (alternating) double bonds. A simple example of this is 1,3,5-hexatriene. [caption id="attachment_7785" align="alignright" width="340"] Fig. 1. 1,3,5 Cyclohexatriene.[/caption] What If? But what if the ends of that 1,3,5 hexatriene are joined, with the loss of two hydrogen atoms, to make a ring one might be tempted to call 1,3,5-cyclohexatriene? In fact, such a molecule, if flipped left-to-right, is seen to be identical with 2,4,6-cyclohexatriene! The numbers can be dropped and the molecule can simply be named…
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