hydrogen bonding Hydrogen fluoride In ice,each water molecule is held arrange in a zig-zag way by four hydrogen bonds in a in solid state.The tetrahedral configuration. hydrogen bond enthalpy is about 28 kJ/mol
Hydrogen fluoride arrange in a zig-zag way in solid state. The hydrogen bond enthalpy is about 28 kJ/mol
Biological importance of H-bond (a) δ+ peptide chain (b) -peptide chain H6. N-peptide chain HO ● δ+
Biological importance of H-bond
Solubility in Water TABLE 10-3 Solubility of Alcohols in Water (at 25C) H Solubility Alcohol in Water CH3一CH2一CH2一CH2 hydrophilic region methyl miscible hydrophobic region ethyl miscible n-propyl miscible t-butyl miscible isobutyl 10.0% n-butyl 9.1% H H n-pentyl 2.7% cyclohexyl 3.6% Solubility decreases as the size n-hexyl 0.6% phenol 9.3% of the alkyl group increases. hexane-1,6-diol miscible Prentice Hall,Inc
Solubility in Water Solubility decreases as the size of the alkyl group increases
Acidity of Alcohols pKa range:15.5-18.0 (water:15.7) decreases as alkyl group increases. decreases as the bulk of the alkyl group increases. Halogens increase the acidity. Phenol is 100 million times more acidic than cyclohexanol! TABLE 10-4 Acid-Dissociation Constants of Representative Alcohols Alcohol Structure Ka pKa methanol CH3-OH 3.2×10-16 15.5 ethanol CH3CH2-OH 1.3×1016 15.9 2-chloroethanol C1-CH2CH2一OH 5.0×1015 14.3 2.2,2-trichloroethanol Cl3C-CH2-OH 6.3×1013 12.2 isopropyl alcohol (CH3)2CH-OH 3.2×10-17 16.5 t-butyl alcohol (CH3)3C-OH 1.0×1018 18.0 cyclohexanol C6H11一OH 1.0×1018 18.0 phenol C6H5-OH 1.0×1010 10.0 Comparison with Other Acids water H2O 1.8×10-16 15.7 acetic acid CH COOH 1.6×105 4.8 hydrochloric acid HCI 1.6×10+2 -2.2 Copyright 2005 Pearson Prentice Hall.Inc
Acidity of Alcohols ❖pKa range: 15.5-18.0 (water: 15.7) ❖decreases as alkyl group increases. ❖decreases as the bulk of the alkyl group increases. ❖Halogens increase the acidity. ❖Phenol is 100 million times more acidic than cyclohexanol!
Acidity of Alcohols Structural Compound Formula pKa Hydrogen chloride HCI Stronger acid Acetic acid CH3 COOH 4.8 Methanol CH3OH 15.5 Water H2O 15.7 Ethanol CH3 CH2OH 15.9 2-Propanol (CH3)2CHOH Weaker 2-Me thyl-2-propanol (CH3)3COH 18 acid *Also given for comparis on are pK a values for water, acetic acid,and hydrogen chloride
Acidity of Alcohols ( CH3 ) 3 COH ( CH3 ) 2 CHOH CH3 CH2 OH H2 O CH3 OH CH3 COOH Hydrogen chloride HCl Acetic acid Methanol Water Ethanol 2-Propanol 2-Methyl-2-propanol Structural Formula Stronger acid Weaker acid *Also given for comparison are pK a values for water, acetic acid, and hydrogen chloride. Compound pKa -7 15.5 15.7 15.9 17 18 4.8