Ethene addition reactions

Moreno and coworkers published a study on the triplet carbene-ethene addition reaction. This process should involve two steps, namely the formation of a triplet trimethylene 1,3-diradical as an intermediate followed by intersystem crossing and formation of 1. The intermediate may live long enough to permit rotation at the CC bonds. In this way, the stereochemistry of the alkene will be lost and a non-stereospecific addition takes place. Moreno and coworkers calculated for the first step of the reaction C 2C i) H2C = CH2 a barrier of 11 kcalmol" and a reaction energy of -26 kcalmoF at the MP2/3-21G level. (It has to be mentioned in this connection that the 3-21G basis is far too small to lead to reliable energies in correlation calculations and therefore results are just of a qualitative nature ) Activation energies varied from 5 to 17 kcalmoF if CH2 was replaced by the triplet state of CH(CN), CH(BeH) and CHLi ... 

Ethanol is prepared by carbohydrate fermentation and by hydration of ethene (addition reaction) ... 

Figure 6 Schematic representation of models for the ethene + ethene addition reaction...

In an addition reaction, a small molecule (e.g., H2, Cl2, HC1, H20) adds across a double or triple bond. A simple example is the addition of hydrogen gas to ethene in the presense of a nickel catalyst. 

The catalyst is a mixture of copper, zinc oxide, and chromium(lll) oxide. Ethanol is produced in large quantities throughout the world by the fermentation of carbohydrates. It is also prepared by the hydration of ethene in an addition reaction ... 

With both (la) and (2a) above, lateral overlap of the p atomic orbitals on adjacent carbon atoms could lead to the formation of two localised n bonds as shown, and the compounds would thus be expected to resemble ethene, only twice as it were This is indeed found to be the case with (2), but (1) is found to behave differently in terms of its slightly greater stability (referred to above), in spectroscopic behaviour (see below), and in undergoing addition reactions more readily than does an isolated diene (p. 194). On looking more closely, however, it is seen that with (la), but not with (2a), lateral overlap could take place between all four p atomic orbitals on adjacent carbon atoms. Such overlap will result in the formation of four molecular orbitals (Fig. 1.2), two bonding ( and 2) and two anti-bonding (i//3 and 4)—the overlap of n atomic orbitals always gives rise to n molecular orbitals ... 

So, this fact is strong evidence in favor of the intra- and inter-molecular dative P—B bond in 126. In solution, 126 is easily oxidized and undergoes addition reactions with sulfur and selenium, with the formation of the corresponding oxide (166), sulfide (167), or selenide (168) [Eq. (129)]. The 3,P chemical shifts of other compounds (166) (27 ppm), (167) (47 ppm), and (168) (46 ppm) are close to that observed for their structural analogues. These data and the values of dipole moments of 4,3 and 4,5 D for 166 and 167, respectively, make it possible to exclude the formation of intramolecular dative P—B bonds similar to those observed for borylphosphine ethene... 

Much ethanol is manufactured by the hydration of ethene. The reaction is an addition reaction between steam and ethene at 300 °C, in the presence of a solid phosphoric acid catalyst, at a pressure of about 70 atmospheres. 

Polymers can be formed from compounds containing a c=c double bond. Alkenes, such as ethene, can undergo addition polymerisation to form a polymer. A polymer is a compound consisting of very long chain molecules built up from smaller molecular units, called monomers. The polymerisation of ethene, to form poly(ethene), is a free radical addition reaction. 

Recent quantum chemical studies of addition reactions to acenes and other PAHs involve the Diels-Alder reactions of ethene [86] and of 1 Ag oxygen [87] as well as... 

The product of an addition reaction depends on the symmetry of the reactants. A symmetrical alkene has identical groups on either side of the double bond. Ethene, CH2 = CH2, is an example of a symmetrical alkene. An alkene that has different groups on either side of the double bond is called an asymmetrical alkene. Propene, CH3CH=CH2, is an example of an asymmetrical alkene. 

Addition polymerization is a reaction in which monomers with double bonds are joined together through multiple addition reactions to form a polymer. Figure 2.12 illustrates the addition polymerization reaction of ethene to form polyethene. Table 2.1, on the next page, gives the names, structures, and uses of some common polymers that are formed by addition polymerization. 

The mechanism for the halogen-alkene addition reaction is a two-step process and is illustrated below using bromine and ethene. 

Ethene or ethylene is the most important organic chemical used in commercial applications. Annual production of ethylene in the United States was over twenty-five million tons in the year 2000. Propylene is also used in large quantities with an annual production of over thirteen million tons. Alkenes such as ethylene and propylene have the ability to undergo addition polymerization. In this process, multiple addition reactions take place and many molecules link together to form a polymer. A polymer is a long chain of repeating units called monomers. For example, the addition of two ethylene molecules can be represented as... 

Figure 8.5, for example, shows that the yield of formic acid first increases and then decreases as the SOz concentration increases, as expected from the competition of reactions (9) and (10) for the adduct. At the same time, as seen in Fig. 8.6, the increased yield of HCHO upon addition of S02 to the ethene-ozone reaction was equivalent to the consumption of S02 (Hatakeyama et al., 1986). 

Other research in tire area of addition reactions onto unsaturated carbon-carbon bonds has included measurement of the rate coefficients for tire addition of NO3 to chloro- and trichloro-ethene,147 relative rate measurement for N03 addition to isoprene,148 TF-/(SR-measured muonium addition to vinyl aromatics12 and EPR studied addition of radical (65) to alkenes.150 In this latter study a linear dependence of the rate constant of addition with tire donor/acceptor properties of the alkene partner was highlighted. 

Another important addition reaction is the one used in the manufacture of ethanol. Ethanol has important uses as a solvent and a fuel (p. 94). It is formed when water (as steam) is added across the double bond in ethene. For this reaction to take place, the reactants have to be passed over a catalyst of phosphoric(v) acid (absorbed on silica pellets) at a temperature of 300 °C and pressure of 60 atmospheres (1 atmosphere =... 

The addition reaction between bromine dissolved in an organic solvent, or water, and alkenes is used as a chemical test for the presence of a double bond between two carbon atoms. When a few drops of this bromine solution are shaken with the hydrocarbon, if it is an alkene, such as ethene, a reaction takes place in which bromine joins to the alkene double bond. This results in the bromine solution losing its red/brown colour. If an alkane, such as hexane, is shaken with a bromine solution of this type, no colour change takes place (Figure 14.13). This is because there are no double bonds between the carbon atoms of alkanes. 

Addition polymer A polymer formed by an addition reaction. For example, poly(ethene) is formed from ethene. 

In Chapter 14 (p. 226) you studied the different addition polymers produced from alkenes. Not all polymers are formed by addition reactions, though. Some are produced as a result of a different type of reaction. In 1935 Wallace Carothers discovered a different sort of plastic when he developed the thermoplastic, nylon. Nylon is made by reacting two different chemicals together, unlike poly(ethene) which is made only from monomer units of ethene. Poly(ethene), formed by addition polymerisation, can be represented by ... 

In the preparation of polyethylene, ethene molecules (C2H4) are bonded together to form a long carbon chain, with two hydrogen atoms bonded to each internal carbon atom and three hydrogen atoms bonded to the end carbon atoms. Draw polyethylene and explain why the formation of polyethylene is an addition reaction. 

An addition reaction is a chemical reaction in which two atoms or groups of atoms add to opposite ends of a carbon-carbon double bond (-C = C-). One of the simplest and most common addition reactions is the one that results in the formation polyethylene. This polymer is formed when many ethene (ethylene) molecules combine with each other ... 

The second important use of superbases is side-chain alkylation of aromatic compounds [22, 34]. In these reactions a benzyl anion generated by the superbase catalyst subsequently attacks olefins such as ethene or propene as a nucleophile. The result of such a nucleophilic addition of a carbanion is side-chain alkylation of the arene by ethene. The reaction was commercialized by Sumitomo for the side-chain alkylation of cumene (Scheme 5, a) [34]. 

By refining the stoichiometry of the oxide overlayer in more detail as we have just done, two types of O species are now predicted to coexist on the oxidized Ag surface. Since the additional adsorbed O atoms are more loosely bound than O atoms adsorbed on bare Ag lll and the O atoms within the oxide ring, it is likely that their reactivity will be different. We aim at examining the reactivity of these two types of O atoms. It is possible that this will prove to be an important step towards understanding the selectivity question in the ethene epoxidation reaction. 

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