Naming the Alkenes

A carbon-carbon double bond is the characteristic functional group of the alkenes. Their general formula is C H2 , the same as that for the cycloalkanes. 

Like other organic compounds, some alkenes are stiU known by conunon names, in which the -ane ending of the corresponding alkane is replaced by -ylene. Substituent names are added as prefixes. 

In lUPAC nomenclature, the simpler ending -ene is used instead of -ylene, as in ethene and propene. More complicated systems require adaptations and extensions of the rules for naming alkanes (Section 2-6). 

Rule 1. To name the stem, find the longest chain that includes both carbons making up the double bond. The molecule may have longer carbon chains, but ignore them. 

Rule 2. Indicate the location of the double bond in the main chain by number, starting at the end closer to the double bond. (CycloaUcenes do not require the numerical prefix, but the carbons making up the double bond are assigned the numbers 1 and 2, unless another group takes precedence see rule 6.) Alkenes that have the same molecular formula but differ in the 

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Self-Test 18.3A (a) Name the alkene (CH3),CHCH=CH2 and (b) write the condensed structural formula for 2-methylpropene. 

Name the alkene that is formed hy the elimination of 2-methyl-2-propanol. 

The rales of the IUPAC system for naming the alkenes are as follows 1. Select as the parent structure the longest continuous chain that contains the carbon-carbon double bond then consider the compound to have been derived from this structure by replacement of hydrogen atoms by various alkyl groups. 

Epoxides are also named as alkene oxides, since they are often prepared by adding an O atom to an alkene (Chapter 12). To name an epoxide this way, mentally replace the epoxide oxygen by a double bond, name the alkene (Section 10.3), and then add the word oxide. For example, the common name for oxirane is ethylene oxide, since it is an epoxide derived from the alkene ethylene. We will use this common method of naming epoxides after the details of alkene nomenclature are presented in Chapter 10. 

Predict the major product in each of the following reactions. Name the alkene reactant and the product, using I.U.P.A.C. names. 

Thus, it emerges that there are six different pathways involved in the ODH reaction scheme r 1 to re. These are shown in Scheme 15.1. Scheme 15.1 shows that propene may be formed as a primary product CO may be formed as a primary and secondary product and, CO2 may be formed as a primary, secondary, and tertiary product. In the scheme, no changes in the catalyst are incorporated and only the state of the gas-phase carbon containing molecules are considered. Furthermore, for the ODH of -butane the formation of butadiene also needs to be considered. The different pathways shown do not necessarily contain a single route by which the particular reactant is converted to the product. For example, ri may contain two routes for converting propane to propene. The objective of the catalyst is to maximize the amount of the desirable product, namely the alkenes, that is, maximize r. ... 

Epoxides can be named as alkene oxides by mentally replacing the epoxide oxygen by a double bond. Name the alkene (Chapter 10) and add the word oxide. 

Name the alkene from which the epoxide can be derived and add the word oxide. 

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