|
Cyclobutadiene is the smallest ''n''-annulene (4-annulene), an extremely unstable hydrocarbon having a lifetime shorter than five seconds in the free state. It has chemical formula 44 and a rectangular structure verified by infrared studies. This is in constrast to the square geometry predicted by simple Hückel theory. Though it has alternating single and double bonds, it fails Hückel's rule, because its ring has 4 π-electrons, and 4 is not twice an odd number. Some cyclobutadiene-metal compounds are stable because the metal atom provides 2 more electrons to the system, The pi electron energy of cyclobutadiene is higher than that of its open-chain counterpart, 1,3-butadiene, and it is therefore said to be antiaromatic rather than aromatic. As a result, it is highly reactive and has a very short lifetime. Cyclobutadiene dimerizes by a Diels-Alder reaction at 35 K. After numerous attempts, it was first synthesized in 1965 by Rowland Pettit of the University of Texas, although he could not isolate it. Cyclobutadiene can be generated through degradation from a cyclobutadiene metal compounds for example 44()3 with ammonium cerium(IV) nitrate. This cyclobutadieneiron tricarbonyl complex was prepared from 4()9 and cis-dichlorocyclobutene . Cyclobutadiene when liberated from the iron complex reacts with electron-deficient alkynes to a Dewar benzene The Dewar benzene converts to dimethyl phthalate on heating at 90°C.
See also | ||||||||
|
| |||||||||
 |
|
| |