Why Cyclodecapentaene is Not an Aromatic Hydrocarbon

[caption id="attachment_16073" align="alignright" width="440"] Fig 1. Cyclodecapentaene - all cis form.[/caption] There are aromatic hydrocarbons and there are non-aromatic hydrocarbons. For basic mono-ring structures that have alternating carbon-carbon double bonds, there is a rule called Hückel’s rule that defines whether a given hydrocarbon can be aromatic or not. It might seem, at first that cyclodecapentaene (C10H10 or [10]-annulene) should be aromatic. Yet, cyclodecapentaene is not an aromatic hydrocarbon. Let’s find out why not. A Few Simple Rules for Aromatic Behavior  The double bonds in the ring must be conjugated (alternating). This allows for the electrons to be delocalized [in conceptualization be flipped in either a clockwise or counterclockwise direction]. This allows for the presence of what is called a ring current.  The ring must be flat.  The mono-ring must feature…
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