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Fulvenes are the class of
Fulvenes are the class of hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
obtained by formally cross-conjugating one ring
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and methylidene through a common exocyclic
In organic chemistry, an alicyclic compound contains one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached.
Cyc ...
double bond
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
.
The name is derived from fulvene
Fulvene (pentafulvene) is a hydrocarbon with the formula (CH=CH)2C=CH2. It is a prototype of a cross-conjugated hydrocarbon. Fulvene is rarely encountered, but substituted derivatives ( fulvenes) are numerous. They are mainly of interest as ligan ...
, which has one pentagonal ring. Other examples include methylenecyclopropene
3-Methylenecyclopropene, also called methylenecyclopropene or triafulvene, is a hydrocarbon with chemical formula . It is a colourless gas that polymerizes readily as a liquid or in solution but is stable as a gas.W. E. Billups , Long Jin Lin , Ed ...
(triafulvene) and heptafulvene.
Fulvenes are generally named based on the number of ring atoms. Thus methylenecyclopropene
3-Methylenecyclopropene, also called methylenecyclopropene or triafulvene, is a hydrocarbon with chemical formula . It is a colourless gas that polymerizes readily as a liquid or in solution but is stable as a gas.W. E. Billups , Long Jin Lin , Ed ...
is "triafulvene", methylenecyclopentadiene is " pentafulvene", etc.
Preparation
Fulvenes are readily prepared by the condensation ofcyclopentadiene
Cyclopentadiene is an organic compound with the chemical formula, formula C5H6. It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−.
This colorless liquid has a strong and unpleasant odor. At room temperature, ...
and aldehyde
In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
s and ketone
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
s:
:C5H6 + R2C=O → C4H4C=CR2 + H2O
Johannes Thiele Johannes Thiele may refer to:
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*Johannes Thiele (chemist)
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is credited with discovering this reaction.
Modern synthesis of fulvenes employ buffer systems.
Properties
The cross-conjugation generally destabilizes the exocyclic double bond, as (per Hückel's rules) polarization of the π electrons would lead to an aromatic ring ion. Consequently, fulvenes add nucleo- and electrophiles easily. They also have a small HOMO-LUMO gap, typically leading to the eponymous visible coloration (" fulvus" is Latin for "yellow").Ligand in organometallic chemistry
Fulvenes are common ligands and ligand precursors inorganometallic chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
. 2,3,4,5-Tetramethylfulvene, abbreviated Me4Fv, results from the deprotonation of cationic pentamethylcyclopentadienyl
1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic diene with the formula , often written , where Me is . It is a colorless liquid.
1,2,3,4,5-Pentamethylcyclopentadiene is the precursor to the ligand ''1,2,3,4,5-pentamethylcyclopentadienyl'', whi ...
complexes. Some Me4Fv complexes are called tuck-in complexes.
References
{{Authority control Cycloalkenes