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1、CHAPTER 19 CARBOXYLIC ACIDS C arboxylic acids, compounds of the type , constitute one of the most fre- quently encountered classes of organic compounds. Countless natural products are carboxylic acids or are derived from them. Some carboxylic acids, such as acetic acid, have been known for centuries
2、. Others, such as the prostaglandins, which are pow- erful regulators of numerous biological processes, remained unknown until relatively recently. Still others, aspirin for example, are the products of chemical synthesis. The therapeutic effects of aspirin, welcomed long before the discovery of pro
3、staglandins, are now understood to result from aspirins ability to inhibit the biosynthesis of prostaglandins. The chemistry of carboxylic acids is the central theme of this chapter. The impor- tance of carboxylic acids is magnifi ed when we realize that they are the parent com- pounds of a large gr
4、oup of derivatives that includes acyl chlorides, acid anhydrides, esters, and amides. Those classes of compounds will be discussed in the chapter fol- CH3COH O Acetic acid (present in vinegar) HO OH O (CH2)6CO2H (CH2)4CH3 PGE1 (a prostaglandin; a small amount of PGE1 lowers blood pressure significan
5、tly) Aspirin COH O O OCCH3 RCOH O X 736 BackForwardMain MenuTOCStudy Guide TOCStudent OLCMHHE Website lowing this one. Together, this chapter and the next tell the story of some of the most fundamental structural types and functional group transformations in organic and bio- logical chemistry. 19.1C
6、ARBOXYLIC ACID NOMENCLATURE Nowhere in organic chemistry are common names used more often than with the car- boxylic acids. Many carboxylic acids are better known by common names than by their systematic names, and the framers of the IUPAC nomenclature rules have taken a lib- eral view toward accept
7、ing these common names as permissible alternatives to the sys- tematic ones. Table 19.1 lists both the common and the systematic names of a number of important carboxylic acids. Systematic names for carboxylic acids are derived by counting the number of car- bons in the longest continuous chain that
8、 includes the carboxyl group and replacing the -e ending of the corresponding alkane by -oic acid. The fi rst three acids in the table, methanoic (1 carbon), ethanoic (2 carbons), and octadecanoic acid (18 carbons), illus- trate this point. When substituents are present, their locations are identifi
9、 ed by number; numbering of the carbon chain always begins at the carboxyl group. This is illustrated in entries 4 and 5 in the table. 19.1Carboxylic Acid Nomenclature737 TABLE 19.1Systematic and Common Names of Some Carboxylic Acids 1. 2. 3. 4. 5. 6. 7. 9. 10. 11. 12. 8. Methanoic acid Ethanoic aci
10、d Octadecanoic acid 2-Hydroxypropanoic acid 2-Hydroxy-2-phenylethanoic acid Propenoic acid (Z)-9-Octadecenoic acid o-Hydroxybenzenecarboxylic acid Propanedioic acid Butanedioic acid 1,2-Benzenedicarboxylic acid Systematic name Benzenecarboxylic acid Formic acid Acetic acid Stearic acid Lactic acid M
11、andelic acid Acrylic acid Oleic acid Benzoic acid Salicylic acid Malonic acid Succinic acid Phthalic acid Common nameStructural formula HCO2H CH3CO2H CH3(CH2)16CO2H CH3CHCO2H W OH CH2CHCO2H CH3(CH2)7(CH2)7CO2H HH CC HO2CCH2CO2H HO2CCH2CH2CO2H CHCO2H W OH CO2H CO2H OH CO2H CO2H BackForwardMain MenuTO
12、CStudy Guide TOCStudent OLCMHHE Website Notice that compounds 4 and 5 are named as hydroxy derivatives of carboxylic acids, rather than as carboxyl derivatives of alcohols. We have seen earlier that hydroxyl groups take precedence over double bonds, and double bonds take precedence over halo- gens a
13、nd alkyl groups, in naming compounds. Carboxylic acids outrank all the common groups we have encountered to this point. Double bonds in the main chain are signaled by the ending -enoic acid, and their position is designated by a numerical prefi x. Entries 6 and 7 are representative carboxylic acids
14、that contain double bonds. Double-bond stereochemistry is specifi ed by using either the cistrans or the EZ notation. When a carboxyl group is attached to a ring, the parent ring is named (retaining the fi nal -e) and the suffi x -carboxylic acid is added, as shown in entries 8 and 9. Compounds with
15、 two carboxyl groups, as illustrated by entries 10 through 12, are distinguished by the suffi x -dioic acid or -dicarboxylic acid as appropriate. The fi nal -e in the base name of the alkane is retained. PROBLEM 19.1The list of carboxylic acids in Table 19.1 is by no means exhaus- tive insofar as co
16、mmon names are concerned. Many others are known by their common names, a few of which follow. Give a systematic IUPAC name for each. (a)(c) (b)(d) SAMPLE SOLUTION(a) Methacrylic acid is an industrial chemical used in the preparation of transparent plastics such as Lucite and Plexiglas. The carbon chain that includes both the carboxylic acid and the double bond is three carbon atoms in length. The compound is named as a derivative of propenoic acid. It is not nec- essary to locate the posit
