09-21 - 9/21/2009 Choose Choose the order that has the...

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Unformatted text preview: 9/21/2009 Choose Choose the order that has the following acids correctly arranged arranged with respect to increasing acidity. Using the electronegativity elements, predict which of the elements, following following acids would be more acidic. element Zn H electronegativity 1.7 2.1 pKa = -1.74 H H O H H Zn Zn+2 H O H H N H H N H O H O H H + H 1 H O H + H A. B. H H O H H Zn O H Zn O H + H H H Zn O H + H + H O H + H pKa = 7.3 Zn +2 O H 2 Would this equilibrium favor the products or reactants? A. Reactants B. Products What What role does zinc play in the enzyme carbonic anhydrase? anhydrase? O Zn+2 H O H H N N H H N N N H N Carbonic anhydrase + H O O Carbonic anhydrase C O H O H + Zn O H Zn O H + H H + Zn O H Zn O H + N N H pKa = 7.3 O H H + H Cl pKa ~ 6 H Cl + O H H 4 pKa = 7.3 Zn +2 pKa ~ 6 O H 5 pKa = -7 pKa = -1.74 What What role does zinc play in the enzyme carbonic anhydrase? anhydrase? Review: What are some factors that affect acidity? pKa H H C H H C H H H H C H H H C H + H O Zn+2 H O H H N N 50 O + H O Carbonic anhydrase C O H O 16 N H H C H O H H C H O O + H H + Zn O H Zn O H + N H 3.74 O H C O H H C O + H H O C O + O H H O O O + H 6 O H C O 7 1 9/21/2009 Which of the following hydrogens is more acidic? Which C-H bond is the most acidic in the following reaction? C- O O O O O O H O C CH3 + N O C + CH3 H N H H H H O AB O O O O C CH3 H H H O C CH3 + N H O C + CH2 H N O O A. A. B. B. O H C CH2 H 8 9 Which hydrocarbon is the most acidic? Choose Choose the answer that has the following acids correctly increasing arranged with respect to increasing acidity. A. D. propane propane CH3 H C H C H H H H B. E. H CH3 C H C H H H H + H O H H H O H C. F. H + CH3 C H C H propane pKa = 51 s-character 25% (sp3) H propene propene CH3 C C H H propene pKa = 44 propyne CH3 C C H H H + O H H H O H + CH3 H C C H 33% (sp2) propyne CH3 C CH3 H C C H + O H H H O H + CH3 C C H 10 pK pKa = 25 C 50% (sp) 11 Can hydroxide ion convert an acetylene into the conjugated base? base? A. yes B. no Can amide ion convert an acetylene into the conjugated base? What information is needed? What factors contribute to the ionization of an acid? CH3 C H C H + N H H N H H + CH3 C C pKa = 25 pKa = 38 pKa -7 -7 bond energy H Cl ? H + Cl electron transfer H + Cl CH3 C H C H + O H O H + CH3 C C 12 14 pKa = 25 pKa = 16 2 9/21/2009 What factors affect the pKa value of an acid? Choose Choose a possible explanation for the observation that ethane thiol thiol is more acidic than ethanol? A. Sulfur is less electronegative than oxygen. B. The S H bond is weaker than the O H bond. C. Water is a weaker acid than ethane thiol. D. The hydronium ion is a stronger acid than ethane thiol. H Cl Cl bond energy H + Cl Cl electron transfer H + Cl periodic table C N O S F Cl I electron transfer Se Br bond energy 365 kJ/mol ethane thiol pKa = 10.6 ethanol pKa = 15.9 CH3 H CH3 C H C H S H O H + H + H O H H H O H + CH3 H H + CH3 C H C H S H O 16 459 kJ/mol H O H H H O 15 Atom Atom electronegativity and bond energies are two factors that can can affect acidity. 365 kJ/mol 459 kJ/mol H H H C O H H CH CH3 C H S ethane thiol pKa = 10.6 ethanol pKa = 15.9 CH CH3 ethylamine pKa ~ 36 CH CH3 H C H N H 3.5 electronegativity 3.0 H 17 3 ...
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This note was uploaded on 12/25/2009 for the course CHE 320 taught by Professor Ff during the Spring '09 term at SUNY Stony Brook.

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