Naming systems alkenes

The cis-trans naming system used in the previous section works only with disub-stituted alkenes—compounds that have two substituents other than hydrogen on the double bond. With trisubstituted and tetrasubstituted double bonds, a more general method is needed for describing double-bond geometry. (Tiisub-stitnted means three substituents other than hydrogen on the double bond tetrasubstituted means four substituents other than hydrogen.)... 

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. 

The naming system is extended to include alkenes by changing the suffix from -ane to -ene, and to alkynes by the suffix -yne. A number before the suffix gives the location of the multiple bond. The terminal carbon is that closest to the multiple bond it has priority over branching of the carbon skeleton. 

Alkenes are hydrocarbons containing at least one double bond. For alkenes with only one double bond, the empirical formula is CnH2n. The names for all alkenes end with -ene. The naming system on alkenes is the same as alkanes, with the exception of the -ene ending. For example, the two-carbon alkane, C2H6, is called ethane, while the two-carbon alkene, C2H4, is called ethene. 

The naming system for alkynes is the same as for alkenes, except that alkynes do not have geometrical isomers. The triple bond only allows a single group to extend off of the carbon atoms attached by a triple bond, so no cis- or trans- isomers are possible. 

Common Names Most alkenes are conveniently named by the IUPAC system, but common names are sometimes used for the simplest compounds. 

Common names are seldom used except for three simple alkenes ethylene, propylene, and isobutylene. The various alkenes of a given carbon number are, however, sometimes referred to collectively as the pentylenes amylenes), hexylenes, heptylenes, and so on. (One sometimes encounters the naming of alkenes as derivatives of ethylene as, for example, tetramethylethylene for (CH3)20—C(CH3)2.) Most alkenes are named by the lUPAC system. 

Compounds containing double or triple bonds between carbon atoms are said to be unsaturated. The alkenes contain double bonds, alkynes contain triple bonds, and aromatics contain a six-membered ring with three double bonds, objectiva 1, Exercise 2.2. In the lUPAC nomenclature system, alkene names end in -ene, and alkynes end in -yne. 

We form lUPAC names of alkenes by changing the -an- infix of the parent alkane to -en-(Section 3.5). Hence, CH2 = CH2 is named ethene, and CH3CH=CH2 is named propene. In higher alkenes, where isomers exist that differ in the location of the double bond, we use a numbering system. We number the longest carbon chain that contains the double bond in the direction that gives the carbon atoms of the double bond the lower set of numbers. We then use the number of the first carbon of the double bond to show its location. We name branched or substituted alkenes in a manner similar to the way we name alkanes (Section 3.3). We number the carbon atoms, locate the double bond, locate and name substituent groups, and name the main (parent) chain. 

Name each alkene, and, using the cis-trans system, show the configuration about each double bond ... 

Name each alkene and specify its configuration by the E,Z system ... 

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