19.4 Acidity of Carboxylic Acids 741 CH3C CH3C or CH3C( PROBLEM 19.2 Peroxyacetic acid(CH3 C is a weaker acid than acetic acid its Ka is 6.3x 10(pKa 8.2)versus 1.8x 10 for acetic acid (pKa 4.7). Why are peroxy acids weaker than carboxylic acids? Electron delocalization in carboxylate ions is nicely illustrated with the aid of elec- trostatic potential maps. As Figure 19.4 shows, the electrostatic potential is different for the two different oxygens of acetic acid, but is the same for the two equivalent oxygens Likewise, the experimentally measured pattern of carbon-oxygen bond lengths in acetic acid is different from that of acetate ion. Acetic acid has a short C=O and a long C-O distance In ammonium acetate, though, both carbon-oxygen distances are equal CH3 CH,O +H △G°=64kJ/mol (15.2 kcal/mol) (21.7 kcal/mol) CH CO +H FIGURE 19.3 Diagram (6.5 kcal/mol) of ionization of ethanol and acetic acid in water. the elec prostatic potential maps of CH3 CH,OH ethoxide and acetate ior Ethanol show the concentration of CH3COH negative charge in ethoxide sus dispersal of charge Acetic acid acetate Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsitePROBLEM 19.2 Peroxyacetic acid is a weaker acid than acetic acid; its Ka is 6.3  109 (pKa 8.2) versus 1.8  105 for acetic acid (pKa 4.7). Why are peroxy acids weaker than carboxylic acids? Electron delocalization in carboxylate ions is nicely illustrated with the aid of elec￾trostatic potential maps. As Figure 19.4 shows, the electrostatic potential is different for the two different oxygens of acetic acid, but is the same for the two equivalent oxygens of acetate ion. Likewise, the experimentally measured pattern of carbon–oxygen bond lengths in acetic acid is different from that of acetate ion. Acetic acid has a short CœO and a long C±O distance. In ammonium acetate, though, both carbon–oxygen distances are equal. (CH3COOH) O X CH3C O O CH3C O O or CH3C O1/2 O1/2 19.4 Acidity of Carboxylic Acids 741 CH3CH2O– +H+ CH3CH2OH ∆G° = 91 kJ/mol (21.7 kcal/mol) ∆G° = 27 kJ/mol (6.5 kcal/mol) ∆G° = 64 kJ/mol (15.2 kcal/mol) Ethanol Acetic acid CH3CO– +H+ O CH3COH O FIGURE 19.3 Diagram comparing the free energies of ionization of ethanol and acetic acid in water. The elec￾trostatic potential maps of ethoxide and acetate ion show the concentration of negative charge in ethoxide versus dispersal of charge in acetate. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website