Ionic Hydrocarbons?

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Offline Kryptid

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Ionic Hydrocarbons?
« on: 22/01/2005 04:06:49 »
When it comes to chemistry, I'm big on hypotheticals.

In the substance known as tropylium bromide, there is a 7-membered, conjugated ring of carbon atoms with a positive charge (it's like a benzene molecule with 7 carbons instead of 6), and a bromide ion. Normally, one would expect this substance to be nonionic, with the bromine atom attached covalently to an sp3 carbon on the ring. However, the tropylium ring can become aromatic if that bromine atom is disconnected from the ring, which gives the ring 3 electron pairs in its pi orbitals. Since this ionic, aromatic form is much more stable than the covalent, nonaromatic form, this substance exists as an ionic compound.

I found that to be quite interesting. There is also another ion, called the cyclopentadienyl anion, which is a 5-carbon ring with a negative charge, which is also aromatic.

I was thinking, perhaps, this cyclopentadienyl anion could be reacted with the tropylium cation to form an ionic hydrocarbon called tropylium cyclopentadienide. The form of the compound which would link the rings together via a covalent bond would interrupt the aromatic character of both rings, thus resulting in an unfavorable molecule. Therefore, I believe that the molecule would exist in the ionic form, since the aromaticity of both rings would make it much more stable.

Does this compound or any other ionic hydrocarbons exist?

I figure that it might be synthesized by reacting tropylium bromide with lithium cyclopentadienide, perhaps in solution:

C7H7Br + LiC5H5 --> C12H12 + LiBr

The idea of an ionic hydrocarbon seems interesting to me, but I'm not too sure of what kind of useful applications it would have. It would be soluble in water, unlike most other nonpolar hydrocarbons. Any ideas on its potential uses?

Other potential ionic hydrocarbons would be:

-cyclopropenyl cyclopentadienide (C8H8)
-cyclopropenyl cyclononatetraenide (C12H12)
-cropylium cyclononatetraenide (C16H16)
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Offline anthony

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Re: Ionic Hydrocarbons?
« Reply #1 on: 21/05/2005 14:27:31 »
The examples you state are vaguely familiar to me, as they are the types of molecules used to exemplify the 4n+2 rule of aromaticity, look it up, you'll like it. There are plenty of "carbocations" and "carboanions" in chemistry, they can be aromatic, conjugated or saturated and have plenty of uses in making larger molecules in synthesis. n-Butyl lithium, is a common reagent, carboanion, it is commonly used as a very strong base. The t-butyl carbocation is also a regular in reaction mechanisms, though not stable in itself enough to be a reagent, it's use is commonly as a protecting group.