CHAPTER NINETEEN Carboxylic Acids 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 and 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 prefix. Entries 6 and 7 are representative carboxylic acids that contain double bonds. Double-bond stereochemistry is specified by using either the cis-trans or the e-Z notation When a carboxyl group is attached to a ring, the parent ring is named(retaining the final -e) and the suffix - carboxylic acid is added, as shown in entries 8 and 9 Compounds with two carboxyl groups, as illustrated by entries 10 through 12,are distinguished by the suffix -dioic acid or-dicarboxylic acid as appropriate. The final -e in the base name of the alkane is retained PROBLEM 19.1 The list of carboxylic acids in Table 19. 1 is by no means exhaus- tive insofar as common names are concerned. many others are known by their common names, a few of which follow. Give a systematic IUPAC name for each (a) CH2-CCO,H (c) HO2 CCO2H (b)H3C CO,H CO2H (p-Toluic acid) 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 position of the double bond by number, as in 2-propenoic acid, "because no other positions are structurally possible for it. The methyl group is at C-2, and so the correct systematic name for methacrylic acid is 2-methyl 19.2 STRUCTURE AND BONDING The structural features of the carboxyl group are most apparent in formic acid. Formic acid is planar, with one of its carbon-oxygen bonds shorter than the other, and with bond angles at carbon close to 1200 Bond distances Bond Angles H-C=0 134 H oxidization at carbon, and a o T carbon-oxygen double bond analogous to that of aldehydes and ketones Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsiteNotice 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 and 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 prefix. Entries 6 and 7 are representative carboxylic acids that contain double bonds. Double-bond stereochemistry is specified by using either the cis–trans or the E–Z notation. When a carboxyl group is attached to a ring, the parent ring is named (retaining the final -e) and the suffix -carboxylic acid is added, as shown in entries 8 and 9. Compounds with two carboxyl groups, as illustrated by entries 10 through 12, are distinguished by the suffix -dioic acid or -dicarboxylic acid as appropriate. The final -e in the base name of the alkane is retained. PROBLEM 19.1 The list of carboxylic acids in Table 19.1 is by no means exhaus￾tive insofar as common 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 position of the double bond by number, as in “2-propenoic acid,” because no other positions are structurally possible for it. The methyl group is at C-2, and so the correct systematic name for methacrylic acid is 2-methyl￾propenoic acid. 19.2 STRUCTURE AND BONDING The structural features of the carboxyl group are most apparent in formic acid. Formic acid is planar, with one of its carbon–oxygen bonds shorter than the other, and with bond angles at carbon close to 120°. This suggests sp2 hybridization at carbon, and a carbon–oxygen double bond analogous to that of aldehydes and ketones. Bond Distances CœO C±O 120 pm 134 pm Bond Angles H±CœO H±C±O O±CœO 124° 111° 125° C H O H O CH3 CO2H (p-Toluic acid) C H H CO2H H3C C (Crotonic acid) HO2CCO2H (Oxalic acid) CH2 CH3 CCO2H (Methacrylic acid) 738 CHAPTER NINETEEN Carboxylic Acids Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website