Alkenes common names

We give alkenes lUPAC names by replacing the ane ending of the corresponding alkane with ene The two simplest alkenes are ethene and propene Both are also well known by their common names ethylene and propylene... 

The common names of these alkenes are c/s and trans di tert butylethylene In cases such as this the common names are somewhat more convenient than the lUPAC names because they are more readily associated with molecular structure... 

Three membered rings that contain oxygen are called epoxides At one time epox ides were named as oxides of alkenes Ethylene oxide and propylene oxide for exam pie are the common names of two industrially important epoxides... 

For historical reasons, there are a few alkenes whose names are firmly entrenched in common usage blit don t conform to the rules. For example, the alkene derived from ethane should be called etheite, but the name ethylene has... 

Table 6.1 Common Names of Some Alkenes Compound Systematic name...

The simplest alkene is ethene, QH4 (common name, ethylene). Its structural formula is... 

A few of the common names that are often encountered for alkenes and groups containing double bonds are listed in Table 5.5. 

Alkenes as Substituents Alkenes named as substituents are called alkenyl groups. They can be named systematically (ethenyl, propenyl, etc.), or by common names. Common alkenyl substituents are the vinyl, allyl, methylene, and phenyl groups. The phenyl group (Ph) is different from the others because it is aromatic (see Chapter 16) and does not undergo the typical reactions of alkenes. 

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

Hydroboration-Oxidation In Section 8-7 we saw that hydroboration-oxidation adds water across the double bonds of alkenes with anti-Markovnikov orientation. A similar reaction takes place with alkynes, except that a hindered dialkylborane must be used to prevent addition of two molecules of borane across the triple bond. Di(second-ary isoamyl)borane, called disiamylborane, adds to the triple bond only once to give a vinylborane. (Amyl is an older common name for pentyl.) In a terminal alkyne, the boron atom bonds to the terminal carbon atom. 

This synthesis of glycols is reflected in their common names. The glycol is named for the alkene from which it is synthesized ... 

The common names of glycols can be awkward and confusing because the -ene portion of the name implies the presence of an alkene double bond, but the glycol does not contain a double bond. We will generally use the IUPAC dk>l nomenclature for diols, but be aware that the names ethylene glycol (automotive antifreeze) and propylene glycol (used in medicines and foods) are universally accepted for these common diols. 

Epoxides (Oxiranes) We have already encountered some of the chemistry of epoxides in Section 8-12. Epoxides are three-membered cyclic ethers, usually formed by peroxyacid oxidation of the corresponding alkenes. The common name of an epoxide is formed by adding oxide to the name of the alkene that is oxidized. The following reactions show the synthesis and common names of two simple epoxides. 

Alkynes are similar to both alkanes and alkenes because they form a homologous series. Alkynes have the general formula of CnH2n-2- So, for example, the first member of the alkyne series, ethyne, has the formula C2H2. (You may know this compound by its common name acetylene.) The next member, propyne, has the formula C3H4. 

Table 20.2 Systematic Name The First Four Unbranched Alkenes Common Molecular Name Formula Structural Formula Line Formula...

The names and formulas of the first four unbranched alkenes are presented in Table 20.2. (Common names are often used for the smallest members of each class.) Ethylene (ethene) and propylene (propene) are the raw materials used in the manufacture of the common plastics polyethylene and polypropylene. 

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. 

The simplest alkene, CH2=CH2, named in the lUPAC system as ethene, is often called ethylene, its common name. The common names for three alkyl groups derived from alkenes are also used. Two examples of naming organic molecules using these common names are shown in Figure 10.3. 

When there is a triple bond in the chain, it is referred to as an alkyne. The names end with yne instead of ane, but otherwise are named similarly to the alkanes and alkenes. Chains with multiple triple bonds are likewise called alkadiynes, with names ending in adiyne alkatriynes, with names ending in atriyne and so forth. The exception is that the compound acetylene (CH CH) retains its common name, Unsaturated hydrocarbon chains are numbered starting at the end of the chain that gives the double or triple bonds the lowest numbers. See Figure 1.10. 

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. 

For historical reasons, there are a few alkenes whose names are firmly entrenched jn common usage but don t conform to the rules. For example, the alkene derived from ethane should be called ethene, but the name ethylene has been used so long that it is accepted by lUPAC. Table 6.1 lists several other common names that are often used and are recognized by lUPAC. Note also that a =CH2 substituent is called a methylene group, a H2C=CH substituent is called a vinyl group, and a H2C=CHCH2- substituent is called an allyl group ... 

Naming alkenes Alkenes are named in much the same way as alkanes. Their names are formed by changing the -ane ending of the corresponding alkane to -ene. An alkane with two carbons is named ethane, and an alkene with two carbons is named ethene. Likewise, a three-carbon alkene is named propene. Ethene and propene have older, common names ethylene and propylene, respectively. 

Thermal decomposition of polyethylene in an inert atmosphere starts at about 280° C and occurs mainly following fragmentation and dehydrogenation reactions, the fragmentation being predominant at temperatures below 600° C (see Section 2.2). Hydrocarbons, from 2 carbon atoms up to 90 carbons, were identified in pyrolysates. Three types of fragment molecules are the most common, namely alkenes, alkanes, and a,(B-dienes. Traces of other hydrocarbons also are formed during pyrolysis. Some reactions typical for polyethylene pyrolysis are shown below ... 

---