Alkenes examples

One of the older preparative free-radical reactions is the addition of polyhalomethanes to alkenes. Examples of addition of carbon tetrabromide, carbon tetrachloride, and bromoform have been recorded. The reactions are chain processes that depend on facile abstraction of halogen or hydrogen from the halomethane ... 

When the 7r-systerns of two or more double bonds overlap, as in conjugated dienes and polyenes, the 7r-clccIrons will be delocalized. This has chemical consequences, which implies that the range of possible chemical reactions is vastly extended over that of the alkenes. Examples are various pericyclic reactions or charge transport in doped polyacetylenes. A detailed understanding of the electronic structure of polyenes is therefore of utmost importance for development within this field. We will first discuss the structure of dienes and polyenes based on theoretical studies. Thereafter the results from experimental studies are presented and discussed. 

Substitution of methyl for hydrogen at the a carbon of an oxime causes an upheld shift of the nitrogen resonance. Although these shifts are similar in direction, they are about twice the magnitude of those observed for the corresponding carbons of alkenes. Examples are... 

The reaction of an alkene (in excess) with a polyhydride can strip hydrogen from the metal. The open sites formed in this process can now react, whether by cyclometalation or by coordinating the alkenes. If the alkene has accessible C—H bonds (e.g. propene) these may be broken by the metal. Indeed dehydrogenation may proceed until a stable 16-electron compound has been formed. In most cases this hydrogen stripped from the ligand is passed to the excess of alkene. Examples of these types of reaction have been described by Wilkinson (Scheme 5).131... 

Finally it should be mentioned that many other compounds containing C-C- and C-O double bonds afford cyclobutanes on irradiation in the presence of alkenes. Examples of monocyclic compounds include endiones,... 

Hofmann elimination usually gives the least substituted alkene. Example i 2 3 4 150 °C... 

These reactions give high yields with 1-alkenes, as shown, but are less satisfactory with alkynes or non-terminal alkenes. Examples of these reactions are also given in Table 3.8, and procedures for hydromagnesation by both Grignard reagents and magnesium hydride follow. 

Codimerisation occurs not only between different fluoroalkenes but also between fluoroalkenes and other unsaturated hydrocarbons. Moreover, some of these codimerisa-tions proceed more readily than the reactions involving only fluorinated alkenes. Examples of addition reactions of fluoroalkenes are shown in Table 7.13. Rate constants have been measured for [2tt + 2tt] and [2tt + 4tt] cycloadditions involving fluorinated alkenes, employing gas-phase NMR techniques [227]. 

Acyl radicals are very useful synthetic intermediates. Their preparation is not simple since the corresponding halides are highly electrophilic and cannot be used as radical precursors. Organocobalt compounds were proposed as suitable source of acyl radicals [44]. However, the use of acyl selenides proved to be more general [45, 46]. These radical precursors can be efficiently prepared from the corresponding carboxylic acids and esters [47]. Acyl phenyl selenides should be preferred, when possible, relative to acyl methyl selenides due to the consumption of two equivalents of tin hydride with this last system (Scheme 1) [4]. Acyl selenides have found many applications in tandem radical additions to alkenes. Examples of intermole-cular [Eq. (18)] [48,49] and intramolecular reactions [Eq. (19)] [50a] are reported. The enoyl selenide 68 give the unsaturated acyl radicals 69. This intermediate... 

Since cationic polymerization involves carbocations, addition follows Markovnikov s rule to form the more stable, more substituted carbocation. Chain termination can occur by a variety of pathways, such as loss of a proton to form an alkene. Examples of alkene monomers that undergo cationic polymerization are shown in Figure 30.4. 

The regioselectivity is not as good with allylic alcohols as it is with unsaturated carbonyl compounds as there is only a steric preference for transfer of the aryl group to the end of the alkene. Examples 224 and 226 show how this can be improved with extra substitution.40... 

Examples of name reactions may be found by first considering the nature of the starting material and product. The Wittig reaction, for instance, is given in Section 199 (Alkenes from Aldehydes) and in Section 207 (Alkenes from Ketones). The aldol condensation may be found in the chapters on difunctional compounds in Section 324 (Alcohol, Thiol-Aldehyde) and in Section 330 (Alcohol, Thiol-Ketone). Examples of the synthetically important alkene metathesis reaction are provided primarily in Section 209 (Alkenes from Alkenes). Examples of the Heck reaction are presented in Section 74C, those for the Suzuki reaction in Section 70, and examples of the Sonogashira reaction are presented in Section 300. 

One of the older preparative free-radical reactions is the addition of poly-halomethanes to alkenes. Examples of addition of carbon tetrabromide, carbon... 

Alkene Example Electrons from Addend Electrons from Alkene... 

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