The Iron Sandwich Compound Ferrocene

[caption id="attachment_6151" align="alignright" width="440"] Ferrocene - an Iron Sandwich Compound[/caption] Who doesn't love a ham and cheese sandwich? Or a peanut butter and jelly sandwich? Well, there are special chemical substances that resemble sandwiches. There is, for example, the sandwich compound ferrocene, (C₅H₅)₂Fe. It consists of an atom of iron "sandwiched" between two cyclopentadiene molecules. Sandwich Compound The classification of such metallic organic compounds is metallocene. D-orbital electrons in the iron atom add to the pi-electrons of two cyclopentadiene molecules. This stabilizes the structure, since the cyclopentadienyl anion (-1 charge) has aromatic properties. The iron atom adopts, in effect, a ferrous (+2) electrical charge. Other Metallocenes In general, metallocenes have mostly been of laboratory interest. Some do exhibit a marked level of importance. One application is in catalysis. Other metallocenes…
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The Aromatic Cyclopentadienyl Anion

Chemistry, Education
[caption id="attachment_16480" align="alignright" width="440"] Cyclopentadienyl Anion[/caption] Is it possible that for an ion to be aromatic? Yes. Consider the aromatic cyclopentadienyl anion. Hückel’s Rule dictates a flat ring with 4n + 2 π (pi) conjugated electrons. The smallest neutral ring with these qualifications has n = 1. It is benzene (C₆H₆). But Hückel’s law does not require an electronically neutral structure. The smallest aromatic ion is the cyclopropenyl cation¹ (C₃H₃⁺). Is there a negative ion that has 6 π electrons and is aromatic? The answer is yes. The aromatic cyclopentadienyl anion (C₅H₅⁻). Neutral Cyclopentadiene Neutral cyclopentadiene is flat. It is pentagon shaped. Three of the carbon-carbon bonds are single bonds. The other two are double bonds. At each of the four ends of the two double bonds there is one…
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