ALKENES, ALKYNES, AND AROMATIC HYDROCARBONS

1) ethylene oligomerization to 1-alkenes and polymerization to different kinds of polyethylene products  

2) addition reactions to the ethylene double bound to yield, for example, ethanol, l,2-dich]oroethane, or styrene  

3) catalytic oxidation of ethylene for the production of ethylene oxide, acetaldehyde, and vinyl acetate. 

Owing to their high industrial relevance, many of the processes named above have been selected as examples of this textbook. They are treated in detail in Sections 6.12 (ethylene oxide production), 6.15 (acetaldehyde production), 6.16 (ethylene oligomerization) and 6.20 (polyethylene production). 

Propylene is also a product of the steam-cracking process (up to 15 wt% of the steam cracker product mix. Section 6.6). In addition, it is obtained by catalytic dehydrogenation of propane (Section 5.3.1) and as a by-product of the FCC process (Section 6.7.2). The technical relevance of propylene as a feedstock for the synthesis of industrial chemical processes has ever increased since the 1960s. The increasing value of propylene can be realized from the fact that propylene was seen in former times as an undesirable by-product of the steam-cracking process and as such it was 

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Functional Groups Defining Alkenes, Alkynes, and Aromatic Hydrocarbons... 

A hydrocarbon is a compound that consists only of carbon and hydrogen atoms. Each contains a skeleton of carbon atoms bonded to varying numbers of hydrogen atoms. Hydrocarbons include alkanes, alkenes, alkynes, and aromatic hydrocarbons. 

Ihe reactivity of alkenes, alkynes, and aromatic hydrocarbons toward electrophiles in addition and substitution reactions is based on their jc-donor abihty. In any reaction involving the attack of an electrophile on a multiple bond, the initial interaction is between the electrophile and the electrons of the tc bond. 

Alumina oxide 200 Alkanes, alkenes, alkynes and aromatic hydrocarbons from Cj to C o- C and C2 halocarbons... 

Because alkanes have only single bonds, they contain the largest possible number of hydrogen atoms per carbon atom. As a result, they are called saturated hydrocarbons. Alkenes, alkynes, and aromatic hydrocarbons contain multiple bonds (double, triple, or delocalized tr bonds). As a result, they contain less hydrogen than an alkane with the... 

SECTION 24.2 The simplest types of organic compounds are hydrocarbons, those composed of only carbon and hydrogen. There are four major kinds of hydrocarbons alkanes, alkenes, alkynes, and aromatic hydrocarbons. Alkanes are composed of only C—H and C—C single bonds. Alkenes contain one or more carbon-carbon double bonds. Alkynes contain one or more carbon carbon triple bonds. Aromatic hydrocarbons contain cychc arrangements of carbon atoms bonded through both saturated hydrocarbons the others are unsaturated. 

Distinguish among alkanes, alkenes, alkynes, and aromatic hydrocarbons. (Section 24.2)... 

Define the terms alkene, alkyne, and aromatic hydrocarbon. 

ALKENES, ALKYNES, AND AROMATIC HYDROCARBONS (SECTION 24.3) The names of alkenes and alkynes are based on the longest continuous chain of carbon atoms that contains the multiple bond, and the location of the multiple bond is specified by a numerical prefix. Alkenes exhibit not only structural isomerism but geometric (cts-trans) isomerism as well. In geometric isomeis, the bonds are the same, but the molecules have different geometries. Geometric isomerism is possible in alkenes because rotation about the C=C double bond is restricted. 

Generally speaking, compounds such as alkanes, whose molecules contain only single bonds, are referred to as saturated compounds because these compounds contain the maximum number of hydrogen atoms that the carbon compound can possess. Compounds with multiple bonds, such as alkenes, alkynes, and aromatic hydrocarbons, are called unsaturated compounds because they possess fewer than the maximum number of hydrogen atoms, and they are capable of reacting with hydrogen under the proper conditions. We shall have more to say about this in Chapter 7. 

Hydrocarbons can be divided into four general types, depending on the kinds of carbon-carbon bonds in their molecules. Figure 25.3 T shows an example of each of the four types alkanes, alkenes, alkynes, and aromatic hydrocarbons. In these hydrocarbons, as well as in other organic compormds, each C atom invariably has four bonds (four single bonds, two single bonds and one double bond, or one single bond and one triple bond). 

Alkenes, alkynes, and aromatic hydrocarbons are much more reactive than the alkanes. Their adsorption requires hardly any activation and the molecules easily establish chemisorption bonds with a surface under vacuum conditions, and at low temperatures. Aromatic hydrocarbons, such as benzene and toluene, usually adsorb with the ring parallel to the surface, but alkenes and alkynes show more variety with respect to surface bonding. 

As shown in Figure 20.1 , we can classify hydrocarbons into four different types alkanes, alkenes, alkynes, and aromatic hydrocarbons. Alkanes, alkenes, and alkynes— also called aliphatic hydrocarbons—are differentiated based on the kinds of bonds between carbon atoms. (We discuss aromatic hydrocarbons in detail in Section 20.7.) As shown in Table 20.1, alkanes have only single bonds between carbon atoms, alkenes have a double bond, and alkynes have a triple bond. 

Since hydrocarbons are important reactants in many heterogeneous catalytic processes on metallic catalysts at both the metal/gas and the metal/electrolyte interfaces, the SERS of alkenes, alkynes, and aromatic hydrocarbons have been investigated at these interfaces. For the metal/gas interface, strong SERS for hydrocarbons has been observed on low-temperature Ag films under UHV conditions, while for the metal/electrolyte interface, pretreated Au electrodes give strong SERS for hydrocarbons adsorbed from aqueous solutions. The SERS of ethylene, propylene, butenes, acetylene, benzene, and benzene derivatives adsorbed on Ag films in the UHV has been discussed by Moskovits and Dilella and Pockrand. ... 

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