Structure and Properties of Carboxylic Acids TABLE15.2 Acidity of Some Carboxylic Acids Structure Ka pKa CF3CO2H 0.59 0.23 Stronger acid HCO2H 1.77×10-4 3.75 HOCH2CO2H 1.5×10-4 3.83 CsHsCO2H 6.46×10-5 4.19 H2C-CHCO2H 5.6×10-5 4.25 CH3CO2H 1.75×10-5 4.76 CH3CH2CO2H 1.34×10-5 4.87 Weaker CH3CH2OH(ethanol) (1.00×10-16) (16.00) acid
Structure and Properties of Carboxylic Acids
Structure and Properties of Carboxylic Acids Carboxylic acids are much weaker acids than mineral acids but much stronger acids than alcohols OH CH3CH2OH CH3COH HCI pKa =16 pKa=9.89 pKa=4.76 pKa=-7 Acidity
Carboxylic acids are much weaker acids than mineral acids but much stronger acids than alcohols Structure and Properties of Carboxylic Acids
Structure and Properties of Carboxylic Acids Carboxylic acids ionize to give resonance stabilized carboxylate ions H20 Ethanol Ethoxide ion (localized charge) :6 Acetic acid H Acetate ion (delocalized charge)
Carboxylic acids ionize to give resonance stabilized carboxylate ions Structure and Properties of Carboxylic Acids
Structure and Properties of Carboxylic Acids Both carbon-oxygen bonds in sodium formate are 127 pm in length,midway between the C=O bond(120 pm)and the C- O bond (134 pm)of formic acid 127pm 120pm Na+ H 134pm O-H Sodium formate Formic acid ngnge Learring All Rights Reserved
Both carbon-oxygen bonds in sodium formate are 127 pm in length, midway between the C=O bond (120 pm) and the CO bond (134 pm) of formic acid Structure and Properties of Carboxylic Acids
15-3 Biological Acids and the Henderson- Hasselbalch Equation At pH 7.3,a value known as physiological pH,both the carboxylic acid and its conjugate base are present The conjugate base form predominates at pH 7.3 Percentages of carboxylic acid and conjugate base can be calculated from the pKa and the pH of the medium i-seo]-的 pK,=-log- [HA] [A PH=pK,+logTHA] Henderson-Hasselbalch equation
At pH = 7.3, a value known as physiological pH, both the carboxylic acid and its conjugate base are present ▪ The conjugate base form predominates at pH = 7.3 ▪ Percentages of carboxylic acid and conjugate base can be calculated from the pKa and the pH of the medium + - - 3 + a 3 - a H O A A p = - log = - log H O - log HA HA A pH = p + log Henderson -Hasselbalch equa on HA ti K K 15-3 Biological Acids and the HendersonHasselbalch Equation