Alkenes Olefins

Carbon can also form multiple bonds with other carbon atoms. This results in unsaturated hydrocarbons such as olefins (alkenes), containing a carbon-carbon double bond, or acetylenes (alkynes), containing a carbon-carbon triple bond. Dienes and polyenes contain two or more unsaturated bonds. 

The use of supported transition metal oxide and Ziegler-Natta-type catalysts for polymerising aliphatic olefins (alkenes) was extended in the 1960s and 1970s to the ring-opening polymerisation of cyclo-olefins. 

The aromatic hydrocarbons are used mainly as solvents and as feedstock chemicals for chemical processes that produce other valuable chemicals. With regard to cyclical hydrocarbons, the aromatic hydrocarbons are the only compounds discussed. These compounds all have the six-carbon benzene ring as a base, but there are also three-, four-, five-, and seven-carbon rings. These materials will be considered as we examine their occurrence as hazardous materials. After the alkanes, the aromatics are the next most common chemicals shipped and used in commerce. The short-chain olefins (alkenes) such as ethylene and propylene may be shipped in larger quantities because of their use as monomers, but for sheer numbers of different compounds, the aromatics will surpass even the alkanes in number, although not in volume. 

Olefin (alkene) metathesis is an important reaction in which all the carbon-carbon double bonds in an alkene are cut and then rearranged in a statistical fashion as shown in Scheme 10.12. 

Olefins (alkenes contain double bonds) =c/ / C2H4,C3H6,C4H8,...,C H2 Ethene, propene, butane (ethylene, propylene, butylene) Diolefins contain two double bonds The compounds are unsaturated since C H2 can be saturated to C H2 +2... 

Styrenes [103], conjugated aT-dienes [107], and aT-enynes [108] are also epoxidized with ketones 57 in high ees (Table 5, entries 9-14). No isomerization of the epoxides was observed therefore only c/x-epoxides were obtained from cis-olefins. Alkenes and alkynes appear to be effective directing groups to favor the desired transition states T and V (Fig. 19). 

Similarly, we can ask what would be the best catalyst for hydrogenating an olefin such as ethylene. Since olefins (alkenes) are more strongly chemisorbed than hydrogen, we choose a metal that just barely chemisorbs H2—this means Co, Rh, Ir, Ni, Pd, or Pt. In practice, nickel is the least expensive choice. Again, it should be finely divided (maximum surface area) for greatest catalytic efficiency and be dispersed on the internal surfaces of a porous support such as alumina with surface area on the order of 200 m2 g 1.8... 

P. R. Blakemore, The Modified Julia Olefination Alkene Synthesis via the Condensation of Metallated Heteroarylalkylsulfones with Carbonyl Compounds, J. Chem. Soc. Perkin Trans. 12002, 2563—2585. 

In the mid to late 1980s, transition-metal catalysts were developed that were particularly useful for carrying out olefin (alkene) metathesis reactions (Rouhi 2002). Metathesis is a reaction in which two molecules containing carbon-carbon double bonds exchange carbon atoms along with any groups attached to them ... 

A type of addition polymer with an olefin (alkene) serving as the monomer. 

J. Salliel and J. L. Charlton, in P. deMayo (ed.), Rearrangements in Ground and Excited States, vol. 3, Academic Press (1980). This chapter provides a detailed account of photochemical c/s-trans isomerization in olefins (alkenes). 

Blakemore, P. R. The modified Julia olefination alkene synthesis via the condensation of metallated heteroarylalkylsulfones with carbonyl compounds. J. Chem. Soc., Perkin Trans. 1 2002, 2563-2585. 

These kinds of processes lead to the internal olefinic (alkene) and the branched paraffinic (alkene) and other branched olefinic products which are characteristic of catalytic cracking processes. 

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