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The process, which is catalyzed by platinum supported by aluminium oxide, is exemplified in the conversion methylcyclohexane (a naphthene) into toluene (an aromatic). [2] Dehydrocyclization converts paraffins (acyclic hydrocarbons) into aromatics. [3] A related aromatization process includes dehydroisomerization of methylcyclopentane to benzene:
A cycloaddition is a reaction that simultaneously forms at least two new bonds, and in doing so, converts two or more open-chain molecules into rings. [3] The transition states for these reactions typically involve the electrons of the molecules moving in continuous rings, making it a pericyclic reaction .
Cyclopentadiene is a highly reactive diene in the Diels–Alder reaction because minimal distortion of the diene is required to achieve the envelope geometry of the transition state compared to other dienes. [11] Famously, cyclopentadiene dimerizes. The conversion occurs in hours at room temperature, but the monomer can be stored for days at ...
The retro-Diels–Alder reaction is used in the industrial production of cyclopentadiene. Cyclopentadiene is a precursor to various norbornenes, which are common monomers. The Diels–Alder reaction is also employed in the production of vitamin B6. Typical route for production of ethylidene norbornene from cyclopentadiene through vinyl ...
CH 3 CH 3 → 2 CH 3 ⋅. Because C−C bond energy is so high (377 kJ/mol), [18] this reaction is not observed under laboratory conditions. More common examples of cracking reactions involve retro-Diels–Alder reactions. Illustrative is the thermal cracking of dicyclopentadiene to produce cyclopentadiene.
An odd number is an indication of the involvement of a charged C atom or of a heteroatom lone pair replacing a CC double bond. Thus, [1,5] and [3,3] shifts become [1,4] and [2,3] shifts with heteroatoms, while preserving symmetry considerations. Hydrogens are omitted in the third example for clarity.
The spontaneous dimerization of neat cyclopentadiene at room temperature to form dicyclopentadiene proceeds to around 50% conversion over 24 hours and yields the endo isomer in better than 99:1 ratio as the kinetically favored product (about 150:1 endo:exo at 80 °C). [6] However, prolonged heating results in isomerization to the exo isomer.
2,3-pentadiene, H 3 C−CH=C=CH−CH 3, with two enantiomers (R and S). [5] It and 1,2-pentadiene are the least common isomers of pentadiene. Well known derivatives containing pentadiene groups include hexadienes , cyclopentadiene , and especially three fatty acids linoleic acid , α- linolenic acid , and arachidonic acid as well as their ...