2.3 The Key Functional Groups In the general equation the functional group(H) is shown explicitly while the remain der of the alkane molecule is abbreviated as R. This is a commonly used notation which helps focus our attention on the functional group transformation without being distracted by the parts of the molecule that remain unaffected. A hydrogen atom in one alkane is very much like the hydrogen of any other alkane in its reactivity toward chlorine. Our ability to write general equations such as the one shown illustrates why the functional roup approach is so useful in organic chemistry A hydrogen atom is a functional unit in alkenes and alkynes as well as in alkanes These hydrocarbons, however, contain a second functional group as well. The car- bon-carbon double bond is a functional group in alkenes, and the carbon-carbon triple bond is a functional group in alkynes A hydrogen atom is a functional group in arenes, and we represent arenes as ArH to reflect this. What will become apparent when we discuss the reactions of arenes, how- ever, is that their chemistry is much richer than that of alkanes, and it is therefore more appropriate to consider the ring in its entirety as the functional group 2.3 THE KEY FUNCTIONAL GROUPS As a class, alkanes are not particularly reactive compounds, and the h in rh is not a particularly reactive functional group. Indeed, when a group other than hydrogen is present on an alkane framework, that group is almost always the functional group Table 2.1 lists examples of some compounds of this type. All will be discussed in later chapters Some of the most important families of organic compounds, those that contain the carbonyl group(C=O), deserve separate mention and are listed in Table 2.2 Carbonyl- discussed group chemistry is containing compounds rank among the most abundant and biologically significant classes chapters( Chapters 17-21) of naturally occurring substances PROBLEM 2.1 Many compounds contain more th functional group. The structure of prostaglandin E,, a hormone that regul ne relaxation of smooth muscles, contains two different kinds of carbonyl gre Classify each one(alde- hyde, ketone, carboxylic acid, ester, amide, acyl chloride, or carboxylic acid anhy dride) TABLE 2.1 unctional Groups in Some Important Classes of Organic Compounds Generalized Representative clas exa Name of example* Alcohol CH3CH2OH Ethanol CH3 CH2CI Chloroethane CH3 CH2NH2 Ethanamine R2C—CR2 H2C—CH2 Oxirane Ether CH3 CH Diethyl ether Nitrile CH3CH2C≡N Propanenitrile alkane NO2 CH3 CH2NO itroethane Thiol RSH CH3 CH2SH Ethanethiol Most compounds have more than one acceptabl The example given is a primary amine(RNH2) Secondary amines have the general structure R NH; tertiary Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteIn the general equation the functional group (±H) is shown explicitly while the remain￾der of the alkane molecule is abbreviated as R. This is a commonly used notation which helps focus our attention on the functional group transformation without being distracted by the parts of the molecule that remain unaffected. A hydrogen atom in one alkane is very much like the hydrogen of any other alkane in its reactivity toward chlorine. Our ability to write general equations such as the one shown illustrates why the functional group approach is so useful in organic chemistry. A hydrogen atom is a functional unit in alkenes and alkynes as well as in alkanes. These hydrocarbons, however, contain a second functional group as well. The car￾bon–carbon double bond is a functional group in alkenes, and the carbon–carbon triple bond is a functional group in alkynes. A hydrogen atom is a functional group in arenes, and we represent arenes as ArH to reflect this. What will become apparent when we discuss the reactions of arenes, how￾ever, is that their chemistry is much richer than that of alkanes, and it is therefore more appropriate to consider the ring in its entirety as the functional group. 2.3 THE KEY FUNCTIONAL GROUPS As a class, alkanes are not particularly reactive compounds, and the H in RH is not a particularly reactive functional group. Indeed, when a group other than hydrogen is present on an alkane framework, that group is almost always the functional group. Table 2.1 lists examples of some compounds of this type. All will be discussed in later chapters. Some of the most important families of organic compounds, those that contain the carbonyl group (CœO), deserve separate mention and are listed in Table 2.2 Carbonyl￾containing compounds rank among the most abundant and biologically significant classes of naturally occurring substances. PROBLEM 2.1 Many compounds contain more than one functional group. The structure of prostaglandin E1, a hormone that regulates the relaxation of smooth muscles, contains two different kinds of carbonyl groups. Classify each one (alde￾hyde, ketone, carboxylic acid, ester, amide, acyl chloride, or carboxylic acid anhy￾dride). 2.3 The Key Functional Groups 55 TABLE 2.1 Functional Groups in Some Important Classes of Organic Compounds Class Alcohol Alkyl halide Amine† Epoxide Ether Nitrile Nitroalkane Thiol Name of example* Ethanol Chloroethane Ethanamine Oxirane Diethyl ether Propanenitrile Nitroethane Ethanethiol *Most compounds have more than one acceptable name. † The example given is a primary amine (RNH2). Secondary amines have the general structure R2NH; tertiary amines are R3N. Representative example CH3CH2OH CH3CH2Cl CH3CH2NH2 CH3CH2OCH2CH3 CH3CH2CPN CH3CH2NO2 CH3CH2SH H2C CH2 O Generalized abbreviation ROH RCl RNH2 ROR RCPN RNO2 RSH R2C CR2 O Carbonyl group chemistry is discussed in a block of five chapters (Chapters 17–21). 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