215F07-notes-11-26-07

215F07-notes-11-26-07 - Chem 215 F07 Notes Dr. Masato...

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Unformatted text preview: Chem 215 F07 Notes Dr. Masato Koreeda - Page 1 of 8. Date: November 26, 2007 Chapter 16-2: Acidity and Basicity of Polyfunctional Compounds I. Polyprotic acids Diprotic acid O O H O O H oxalic acid (found in spinach) pKa 1 1.27; pKa 2 4.27 O O H O O O O O O H inductively electrons are pushed toward the C(=O)OH? stabilized by an intra- molecular H-bonding less acidic than the first C(=O)O H also, considerably more acidic than usual R-C(=O)O H H O O H O O succinic acid (found in amber, fossil, and fungi) pKa 1 4.21; pKa 2 5.64 O O H H OH H O O OH H (+)-tartaric acid (a byproduct in wine making) pKa 1 2.93; pKa 2 4.23 O O H O H O O OH H H low pKa 1 due to the H-bonding of the conjugate base? Acidity Constant (pK a ) AH + H 2 O A- + H 3 O + K e K e = (a A " )(a H3O + ) (a AH )(a H2O ) (a X ) : activity of each species; K e : equilibrium constant At low concentrations, (a H 2 O ) constant. Therefore, K a = K e (a H 2 O ) = (a A " )(a H3O + ) (a AH ) = [A " ][H 3 O + ] [AH] where K a : (thermodynamic) acidity constant [X] : concentration of each species; f : activity coefficient, i.e., (a X ) = f X [X] This equation can be approximated as follows in a dilute solution: K a [A " ][H 3 O + ] [AH] = K a K a = acidity constant pK a = - log K a thus, smaller pK a stronger acid pH vs. pK a Since pH = - log [H + ] = log 1 [H + ] , note: [H + ] = [H 3 O + ] K a = [A " ][H 3 O + ] [AH] can be transformed into pK a = log [AH] [A " ] + pH Note: The pH of a solution can be adjusted by adding an acid or base. Chem 215 F07 Notes Dr. Masato Koreeda - Page 4 of 8. Date: November 26, 2007 15.8, 23.6: Chemical Synthesis of Peptides Peptides : Any polymer of amino acids linked by amide bonds between the amino group of each amino acid and the carbonyl group of the neighboring amino acid. and the carbonyl group of the neighboring amino acid....
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This note was uploaded on 04/01/2008 for the course CHEM 215 taught by Professor Koreeda during the Fall '07 term at University of Michigan.

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215F07-notes-11-26-07 - Chem 215 F07 Notes Dr. Masato...

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