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 Websiteincrease 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 sim￾ilar 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