CARBOXYLIC ACIDS 507 (c) The phenyl and methyl substituents attached to C-2 of malonic acid play no role in the decar ①m OH dioxide 2-Phenylpropanoic acid 19.12 (b) The thermal decarboxylation of B-keto acids resembles that of substituted malonic acids. The structure of 2, 2-dimethylacetoacetic acid and the equation representing its decarboxylation were given in the text. The overall process involves the bonding H O CHaCCH(CH,) H,C H3 2. 2-Dimethylacetoacetic Enol form of 3-methy 3-Methyl-2-butanone 19.13 (a) Lactic acid(2-hydroxypropanoic acid) is a three-carbon carboxylic acid that bears a hydroxyl C-2. CH CHCOH 2-Hydroxypropanoic acid (b The parent name ethanoic acid tells us that the chain that includes the carboxylic acid func tion contains only two carbons. A hydroxyl group and a phenyl substituent are present at C-2. CHCO.H 2-Hydroxy-2-phenylethanoic acid (c) The parent alkane is tetradecane, which has an unbranched chain of 14 carbons. The termi- nal methyl group is transformed to a carboxyl function in tetradecanoic acid. Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(c) The phenyl and methyl substituents attached to C-2 of malonic acid play no role in the decarboxylation process. 19.12 (b) The thermal decarboxylation of -keto acids resembles that of substituted malonic acids. The structure of 2,2-dimethylacetoacetic acid and the equation representing its decarboxylation were given in the text. The overall process involves the bonding changes shown. 19.13 (a) Lactic acid (2-hydroxypropanoic acid) is a three-carbon carboxylic acid that bears a hydroxyl group at C-2. (b) The parent name ethanoic acid tells us that the chain that includes the carboxylic acid function contains only two carbons. A hydroxyl group and a phenyl substituent are present at C-2. (c) The parent alkane is tetradecane, which has an unbranched chain of 14 carbons. The terminal methyl group is transformed to a carboxyl function in tetradecanoic acid. Tetradecanoic acid (myristic acid) CH3(CH2)12COH O 2-Hydroxy-2-phenylethanoic acid (mandelic acid) CHCO2H OH 2-Hydroxypropanoic acid CH3CHCO2H OH 3 21 Enol form of 3-methyl- 2-butanone C CH3 OH CH3C CH3 3-Methyl-2-butanone CH3CCH(CH3)2 O CO2 2,2-Dimethylacetoacetic acid O H C H3C CH3 O C O CH3C C CH3 O C OH O O C H heat CO2 H3C C C OH OH CHCOH O CH3 2-Phenylpropanoic acid Carbon dioxide CARBOXYLIC ACIDS 507 __ __ __ Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
508 CARBOXYLIC ACIDS (d) Undecane is the unbranched alkane with 1l carbon atoms, undecanoic acid is the correspond- carboxylic acid, and undecenoic acid is an 11-carbon carboxylic acid that contains a double bond. Because the carbon chain is numbered beginning with the carboxyl group, 10-undecenoic acid has its double bond at the opposite end of the chain from the carboxyl group H,C=CH(CH2)&CO,H 10-Undecenoic acid (undecylenic acid) (e) Mevalonic acid has a five-carbon chain with hydroxyl groups at C-3 and C-5, along with a methyl group at C-3 HOCH,CH, CCH,CO, H 3. 5-Dihydroxy-3-methylpentanoic acid (f) The constitution represented by the systematic name 2-methyl-2-butenoic acid gives rise to CH CH=CCO.H 2-Methy 1-2-butenoic acid Tiglic acid is the e isomer and the z isomer is known as angelic acid. The higher ranked sub stituents,methyl and carboxyl, are placed on opposite sides of the double bond in tiglic acid and on the same side in angelic acid. H,C H3 (E)-2-Methyl-2-butenoic (Z)-2-Methyl-2-butenoic acid (g) Butanedioic acid is a four-carbon chain in which both terminal carbons are carboxylic acid groups. Malic acid has a hydroxyl group at C-2. HOCCHCHCOH h) Each of the carbon atoms of propane bears a carboxyl group as a substituent in 1, 2, 3-propane- tricarboxylic acid. In citric acid C-2 also bears a hydroxyl group COH HO, CCH, CCH, CO,H 2-Hydroxy-1, 2, 3-propanetricarboxylic acid Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(d) Undecane is the unbranched alkane with 11 carbon atoms, undecanoic acid is the corresponding carboxylic acid, and undecenoic acid is an 11-carbon carboxylic acid that contains a double bond. Because the carbon chain is numbered beginning with the carboxyl group, 10-undecenoic acid has its double bond at the opposite end of the chain from the carboxyl group. (e) Mevalonic acid has a five-carbon chain with hydroxyl groups at C-3 and C-5, along with a methyl group at C-3. ( f) The constitution represented by the systematic name 2-methyl-2-butenoic acid gives rise to two stereoisomers. Tiglic acid is the E isomer, and the Z isomer is known as angelic acid. The higher ranked substituents, methyl and carboxyl, are placed on opposite sides of the double bond in tiglic acid and on the same side in angelic acid. (g) Butanedioic acid is a four-carbon chain in which both terminal carbons are carboxylic acid groups. Malic acid has a hydroxyl group at C-2. (h) Each of the carbon atoms of propane bears a carboxyl group as a substituent in 1,2,3-propanetricarboxylic acid. In citric acid C-2 also bears a hydroxyl group. HO2CCH2CCH2CO2H OH CO2H 2-Hydroxy-1,2,3-propanetricarboxylic acid (citric acid) HO2CCHCH2CO2H OH 2-Hydroxybutanedioic acid (malic acid) C C H H3C CO2H CH3 (E)-2-Methyl-2-butenoic acid (tiglic acid) C C H H3C CH3 CO2H (Z)-2-Methyl-2-butenoic acid (angelic acid) CH3CH CCO2H CH3 2-Methyl-2-butenoic acid HOCH2CH2CCH2CO2H OH CH3 3,5-Dihydroxy-3-methylpentanoic acid (mevalonic acid) 10-Undecenoic acid (undecylenic acid) H2C CH(CH2)8CO2H 508 CARBOXYLIC ACIDS __ __ __ Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
CARBOXYLIC ACIDS 50 (i) There is an aryl substituent at C-2 of propanoic acid in ibuprofen. This aryl substituent is a benzene ring bearing an isobutyl group at the para position. CH3CHCO,H CH,CH(CH3) (p-lsobutylphenyl)- propanoic acid O Benzenecarboxylic acid is the systematic name for benzoic acid. Salicylic acid is a derivative of benzoic acid bearing a hydroxyl group at the position ortho to the carboxyl COH o-Hydroxybenzenecarboxy lic acid (salicylic acid) 19.14 (a) The carboxylic acid contains a linear chain of eight carbon atoms. The parent alkane is octane, and so the systematic name of CH3(CH2)CO,H is octanoic acid (b) The compound shown is the potassium salt of octanoic acid. It is potassium octanoate. (c) The presence of a double bond in CH,=CH(CH)5CO, H is indicated by the ending -enoic acid. Numbering of the chain begins with the carboxylic acid, and so the double bond is be- tween C-7 and C-8. The compound is 7-octenoic acid. (d) Stereochemistry is systematically described by the E-z notation. Here, the double bond be- tween C-6 and C-7 in octenoic acid has the Z configuration; the higher ranked substituents are he same side HaC (CH,)CO,H (Z)-6-Octenoic acid (e) A dicarboxylic acid is named as a dioic acid. The carboxyl functions are the terminal carbons of an eight-carbon chain; HO, C(CH,) CO, H is octanedioic acid. It is not necessary to iden- tify the carboxylic acid locations by number because they can only be at the ends of the chain when the -dioic acid name is used (f) Pick the longest continuous chain that includes both carboxyl groups and name the compound a-dioic acid. This chain contains only three carbons and bears a pentyl group as a sub- stituent at C-2. It is not necessary to specify the position of the pentyl group, because it can nly be attached to C-2 CH3(CH,)CHCO,H Malonic acid is an acceptable synonym for propanedioic acid; this compound may also be named pentylmalonic acid. Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(i) There is an aryl substituent at C-2 of propanoic acid in ibuprofen. This aryl substituent is a benzene ring bearing an isobutyl group at the para position. ( j) Benzenecarboxylic acid is the systematic name for benzoic acid. Salicylic acid is a derivative of benzoic acid bearing a hydroxyl group at the position ortho to the carboxyl. 19.14 (a) The carboxylic acid contains a linear chain of eight carbon atoms. The parent alkane is octane, and so the systematic name of CH3(CH2)6CO2H is octanoic acid. (b) The compound shown is the potassium salt of octanoic acid. It is potassium octanoate. (c) The presence of a double bond in CH2?CH(CH2)5CO2H is indicated by the ending -enoic acid. Numbering of the chain begins with the carboxylic acid, and so the double bond is between C-7 and C-8. The compound is 7-octenoic acid. (d) Stereochemistry is systematically described by the E–Z notation. Here, the double bond between C-6 and C-7 in octenoic acid has the Z configuration; the higher ranked substituents are on the same side. (e) A dicarboxylic acid is named as a dioic acid. The carboxyl functions are the terminal carbons of an eight-carbon chain; HO2C(CH2)6CO2H is octanedioic acid. It is not necessary to identify the carboxylic acid locations by number because they can only be at the ends of the chain when the -dioic acid name is used. ( f ) Pick the longest continuous chain that includes both carboxyl groups and name the compound as a -dioic acid. This chain contains only three carbons and bears a pentyl group as a substituent at C-2. It is not necessary to specify the position of the pentyl group, because it can only be attached to C-2. Malonic acid is an acceptable synonym for propanedioic acid; this compound may also be named pentylmalonic acid. Pentylpropanedioic acid CH3(CH2)4CHCO2H CO2H 2 1 3 C C H H3C H (CH2)4CO2H (Z)-6-Octenoic acid o-Hydroxybenzenecarboxylic acid (salicylic acid) OH CO2H 2-( p-Isobutylphenyl)- propanoic acid CH3CHCO2H CH2CH(CH3)2 CARBOXYLIC ACIDS 509 __ __ __ Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
510 CARBOXYLIC ACIDS (g) A carboxylic acid function is attached as a substituent on a seven-membered ring. The com- olic acid CO,H (h) The aromatic ring is named as a substituent attached to the eight-carbon carboxylic acid Numbering of the chain begins with the carboxyl group CHCH -CH(CH2)CO2H 6-Phenyloctanoic acid 19.15(a) Carboxylic acids are the most acidic class of organic compounds containing only the elements C, H, and O. The order of decreasing acidity is Acetic acid CHaCO, H 18×10-5 Ethanol CH3,OH Ethane H3 CH3 ≈1 (b) Here again, the carboxylic acid is the strongest acid and the hydrocarbon the weakest Benzoic acid CH,CO, H 6.7X 10-5 Benzyl alcohol CBH CH,OH 16-18 C6H6 ≈43 (c) Propanedioic acid is a stronger acid than propanoic acid because the electron-withdrawing effect of one carboxyl group enhances the ionization of the other. Propanedial is a 1,3-dicar- bonyl compound that yields a stabilized enolate; it is more acidic than 1, 3-propanediol. Propanedioic acid HO, CCH, CO, H 14×10-3 Propanoic acid CHa CH,CO, H 1.3×10-5 ≈10 1, 3-Propanediol HOCH,CH, CH,OH 10 ≈16 (d) Trifluoromethanesulfonic acid is by far the strongest acid in the group. It is structurally related to sulfuric acid, but its three fluorine substituents make it much stronger. Fluorine substituents Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(g) A carboxylic acid function is attached as a substituent on a seven-membered ring. The compound is cycloheptanecarboxylic acid. (h) The aromatic ring is named as a substituent attached to the eight-carbon carboxylic acid. Numbering of the chain begins with the carboxyl group. 19.15 (a) Carboxylic acids are the most acidic class of organic compounds containing only the elements C, H, and O. The order of decreasing acidity is Ka pKa Acetic acid CH3CO2H 1.8 105 4.7 Ethanol CH3CH2OH 1016 16 Ethane CH3CH3 1046 46 (b) Here again, the carboxylic acid is the strongest acid and the hydrocarbon the weakest: Ka pKa Benzoic acid C6H5CO2H 6.7 105 4.2 Benzyl alcohol C6H5CH2OH 1016–1018 16–18 Benzene C6H6 1043 43 (c) Propanedioic acid is a stronger acid than propanoic acid because the electron-withdrawing effect of one carboxyl group enhances the ionization of the other. Propanedial is a 1,3-dicarbonyl compound that yields a stabilized enolate; it is more acidic than 1,3-propanediol. Ka pKa Propanedioic acid HO2CCH2CO2H 1.4 103 2.9 Propanoic acid CH3CH2CO2H 1.3 105 4.9 Propanedial O?CHCH2CH?O 109 9 1,3-Propanediol HOCH2CH2CH2OH 1016 16 (d) Trifluoromethanesulfonic acid is by far the strongest acid in the group. It is structurally related to sulfuric acid, but its three fluorine substituents make it much stronger. Fluorine substituents 6-Phenyloctanoic acid CH(CH2)4CO2H CH2CH3 CO2H 510 CARBOXYLIC ACIDS __ __ __ Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
CARBOXYLIC ACIDS 511 ncrease the acidity of carboxylic acids and alcohols relative to their nonfluorinated analogs, but not enough to make fluorinated alcohols as acidic as carboxylic acids Ka Trifluoromethanesulfonic acid CF. OH Trifluoroacetic acid CF3CO2H 59×10-1 CH COH 1.8×10-5 2. 2-Trifluoroethanol CF3CH,OH Ethanol CHCHOH ≈16 (e) The order of decreasing acidity is carboxylic acid> B-diketone ketone hydrocarbon K pk COH Cyclopentanecarboxylic acid 1×10 5.0 2. 4-Pentanedione CH, CCH, CCH3 Cyclopentanone Cyclopentene -4545 19.16 (a) A trifluoromethyl group is strongly electron-withdrawing and acid-strengthening. Its ability to attract electrons from the carboxylate ion decreases as its distance down the chain increases 3, 3,3-Trifluoropropanoic acid is a stronger acid than 4, 4, 4-trifluorobutanoic acid CF CH, CO,H CF3CH,CH,CO, H 3. 3.3-Trifluoropropanoic acid 4, 4.4-TriHluorobutanoic acid k9.6×1 K69×10-3 (pK 3.0) (pK24.2) (b) The carbon that bears the carboxyl group in 2-butynoic acid is sp-hybridized and is, therefore, more electron-withdrawing than the sp-hybridized a carbon of butanoic acid. The anion of 2- butynoic acid is therefore stabilized better than the anion of butanoic acid, and 2-butynoic acid is a stronger acid CH3CECCO, H CH, CH, CH,CO,H Butanoic acid K25 (pk24.8) (c) Cyclohexanecarboxylic acid is a typical aliphatic carboxylic acid and is expected to be sim- lar to acetic acid in acidity. The greater electronegativity of the sp--hybridized carbon Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
increase the acidity of carboxylic acids and alcohols relative to their nonfluorinated analogs, but not enough to make fluorinated alcohols as acidic as carboxylic acids. Ka pKa Trifluoromethanesulfonic acid CF3SO2OH 106 6 Trifluoroacetic acid CF3CO2H 5.9 101 0.2 Acetic acid CH3CO2H 1.8 105 4.7 2,2,2-Trifluoroethanol CF3CH2OH 4.2 1013 12.4 Ethanol CH3CH2OH 1016 16 (e) The order of decreasing acidity is carboxylic acid -diketone ketone hydrocarbon. Ka pKa Cyclopentanecarboxylic acid 1 105 5.0 2,4-Pentanedione 109 9 Cyclopentanone 1020 20 Cyclopentene 1045 45 19.16 (a) A trifluoromethyl group is strongly electron-withdrawing and acid-strengthening. Its ability to attract electrons from the carboxylate ion decreases as its distance down the chain increases. 3,3,3-Trifluoropropanoic acid is a stronger acid than 4,4,4-trifluorobutanoic acid. (b) The carbon that bears the carboxyl group in 2-butynoic acid is sp-hybridized and is, therefore, more electron-withdrawing than the sp3 -hybridized carbon of butanoic acid. The anion of 2- butynoic acid is therefore stabilized better than the anion of butanoic acid, and 2-butynoic acid is a stronger acid. (c) Cyclohexanecarboxylic acid is a typical aliphatic carboxylic acid and is expected to be similar to acetic acid in acidity. The greater electronegativity of the sp2 -hybridized carbon CH3C CCO2H 2-Butynoic acid Ka 2.5 103 (pKa 2.6) CH3CH2CH2CO2H Butanoic acid Ka 1.5 105 (pKa 4.8) CF3CH2CO2H 3,3,3-Trifluoropropanoic acid (pKa 3.0) Ka 9.6 104 CF3CH2CH2CO2H 4,4,4-Trifluorobutanoic acid (pKa 4.2) Ka 6.9 105 O CH3CCH2CCH3 O O CO2H CARBOXYLIC ACIDS 511 __ __ __ Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website