Dolbier HW Solutions 417

Dolbier HW Solutions 417 - 511 CARBOXYLIC ACIDS increase...

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Unformatted text preview: 511 CARBOXYLIC ACIDS 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 Trifluoromethanesulfonic acid Trifluoroacetic acid Acetic acid 2,2,2-Trifluoroethanol Ethanol (e) CF3SO2OH CF3CO2H CH3CO2H CF3CH2OH CH3CH2OH The order of decreasing acidity is carboxylic acid pKa 106 10 1 10 5 10 13 10 16 5.9 1.8 4.2 -diketone 6 0.2 4.7 12.4 16 ketone Ka CO2H O 1 O Cyclopentanone 10 5 5.0 10 9 9 10 20 20 45 45 O CH3CCH2CCH3 2,4-Pentanedione Cyclopentene (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. CF3CH2CO2H CF3CH2CH2CO2H 3,3,3-Trifluoropropanoic acid Ka 9.6 10 4 (pKa 3.0) (b) 4,4,4-Trifluorobutanoic acid Ka 6.9 10 5 (pKa 4.2) 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 2butynoic acid is therefore stabilized better than the anion of butanoic acid, and 2-butynoic acid is a stronger acid. CH3C CCO2H 2-Butynoic acid Ka 2.5 10 3 (pKa 2.6) (c) Back Forward pKa 10 Cyclopentanecarboxylic acid 19.16 hydrocarbon. CH3CH2CH2CO2H Butanoic acid Ka 1.5 10 5 (pKa 4.8) 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 Main Menu TOC Study Guide TOC Student OLC MHHE Website __ __ __ ...
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