Melting Points Aliphatic acids with more than 8 carbons are solids at room temperature. Double bonds (especially cis)lower the melting point.Note these 18-C acids: ●Stearic acid(saturated):72c硬脂酸 ●Oleic acid(one cis double bond):16C油酸 ●Linoleic acid(two cis double bonds):-5c亚油酸 COOH COOH stearic acid,mp 70C oleic acid,mp 4C
Melting Points ◼Aliphatic acids with more than 8 carbons are solids at room temperature. ◼Double bonds (especially cis) lower the melting point. Note these 18-C acids: ⚫Stearic acid (saturated): 72C硬脂酸 ⚫Oleic acid (one cis double bond): 16C油酸 ⚫Linoleic acid (two cis double bonds): -5C亚油酸 硬脂酸,油酸,亚油酸
Solubility Water solubility decreases with the length of the carbon chain. Up to 4 carbons,acid is miscible in water. More soluble in alcohol. Also soluble in relatively nonpolar solvents like chloroform because it dissolves as a dimer
Solubility ◼Water solubility decreases with the length of the carbon chain. ◼Up to 4 carbons, acid is miscible in water. ◼More soluble in alcohol. ◼Also soluble in relatively nonpolar solvents like chloroform because it dissolves as a dimer
Acidity R-0-H+H,ǒ：→ R-0 +H2O+ pK.≡I6 (K,=1016 alcohol alkoxide 0 R-C-0-H+H,0:←2 HO+ pK≡5 (K。=10-) acid carboxylate R-O- + H.O+ R一OH+H2O 0=0X R- HO+ R一COOH+HO stabilization of carboxylate Copyright2005 Pearson Prentice Hall,Inc
Acidity
Substituent Effects on Acidity Any factor which stabilizes the carboxylate anion,increases the acidity. Electron withdrawing groups(EWG)should withdraw electron density from the carboxylate anion and thus increase acidity. Electron donating groups(EDG)have the opposite effect. EWG EDG ◆C一O0 Electron-withdrawing group Electron-donating group stabilizes carboxylate destabilizes carboxylate and strengthens acid and weakens acid 2004 Thom son/Brooks Cole
Substituent Effects on Acidity ◼Any factor which stabilizes the carboxylate anion, increases the acidity. ⚫Electron withdrawing groups (EWG) should withdraw electron density from the carboxylate anion and thus increase acidity. ⚫Electron donating groups (EDG) have the opposite effect
Inductive effects诱导效应 Inductive effects are strongly dependent on distance.The effect of the halogen decreases as the distance increases. FCH2CO2H>CICH2CO2H>BrCH2CO2H>CH3CO2H pKa 2.59 2.87 2.90 4.76 CICCO,H>CICHCO2H>CICH2CO,H>CHCO2H pKa 0.64 1.26 2.87 4.76 CO2H pKa 2.86 4.05 4.52
FCH2CO2H > ClCH2CO2H > BrCH2CO2H > CH3CO2H Cl3CCO2H > Cl2CHCO2H > ClCH2CO2H > CH3CO2H CO2H Cl CO2H Cl CO2H Cl > > pKa pKa pKa 2.59 2.87 2.90 4.76 0.64 1.26 2.87 4.76 2.86 4.05 4.52 Inductive effects 诱导效应 ◼Inductive effects are strongly dependent on distance. The effect of the halogen decreases as the distance increases