Chemistry: What’s a Chromophore?

Chemistry
One online definition of chromophore is "an atom or group whose presence is responsible for the color of a compound." Although one may think of a chromophore that includes a metal atom such as copper, nickel, or cobalt, in organic chemistry a chromophore is more likely to consist of a collection of carbon-carbon multiple bonds, perhaps with modifying features. It is the organic variety we discuss in this article. Multiple Bonds Most organic compounds incorporate one or more of three carbon-to-carbon bond varieties: single bonds, double bonds, triple bonds. When drawing a basic organic compound, these are usually represented by: C–C, C=C, and C≡C, respectively. Although such notations are quite useful, they afford little information concerning bond nature and behavior. Bond Hybridization The best working hypothesis for bonding between atoms…
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Why Cyclodecapentaene is Not an Aromatic Hydrocarbon

Chemistry
[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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