09-24 - 9/24/2010 Choose the order that has the following...

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Unformatted text preview: 9/24/2010 Choose the order that has the following compounds correctly arranged with respect to increasing acidity. A. D. propane pKa = ≈51 CH3 H C H C H H H C N H H H C O H H + CH3 H C H H + CH3 H H H + CH3 Using our concepts of bonding is it possible to predict the relative acidity of acids? O O H + CH3 C O B. E. C. F. electronegativity H C H C H H C H N H H O H acetic acid CH3 C O H H + O H H H O 2.5 pKa = 4.75 Which of these acids would be predicted to be stronger, A or B? trifluoro F C acetic C acid F F O O H + H O H H H O H + F O F C C F O A ethylamine pKa = ≈38 CH3 3.0 B ethanol ethanol pKa = 15.9 CH3 3.5 1 pKa = 0.3 2 electronegativity table Choose the order that has the following acids correctly arranged with respect to increasing acidity. Choose the order that has the following acids correctly arranged with respect to increasing acidity. i ii iii H Zn O H H O H H N H H N H O H H + H 3 Zn O H + H i ii iii H H O H H O H H N H H N H H O H O H H + H 4 + H + H + H Choose the order that has the following acids correctly arranged with respect to increasing acidity. Using the electronegativity elements, predict which of the 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 A. B. H H O H H Zn O H Zn O H + H H H O H H O H H N H H N H O H H + H 5 Zn O H + H O H + H + H pKa = 7.3 Zn +2 O H 6 1 9/24/2010 The hydration of carbon dioxide. Histidine is the amino acid at the active site. Is water behaving as the (A) acid or (B) base in the above reaction? Carbonic anhydrase Carbonic anhydrase A H B N H H Zn O H Zn O H + H + Zn O H Zn H O H + N What is the role of zinc at the active site of carbonic anhydrase? Which conjugate acid is the product, A or B? Would this equilibrium favor the products or reactants? A. Reactants B. Products What role does zinc play in the enzyme carbonic 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 + Zn O H Zn O H + N N H pKa = 7.3 pKa ~ 6 pKa = 7.3 Zn 9 +2 pKa ~ 6 O H 10 Which hydrocarbon is the most acidic? 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 11 pKa = 25 pK C 50% (sp) 12 2 9/24/2010 What factors contribute to the ionization of an acid? What factors affect the pKa value of an acid? H Cl Cl bond energy H + Cl Cl electron transfer H + Cl pKa -7 bond energy H Cl ? H + Cl electron transfer electron transfer H + Cl bond energy 13 14 Which acid is more acidic? Choose a possible explanation for the observation that ethane thiol is more acidic than ethanol? periodic table 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. C N O S F Cl I Se Br 365 kJ/mol H H C S H C O H + H + A B H O H H H O H + CH3 H C H S H C O ethane thiol pKa = 10.6 ethanol pKa = 15.9 CH3 H C H S H C O H + H + H O H H H O H + CH3 H C H S H C O CH3 H CH3 459 kJ/mol H CH3 H O H H H O H + CH3 H H O H H H O H + CH3 H 15 16 Atom electronegativity and bond energies are two factors that can affect acidity. 365 kJ/mol 459 kJ/mol H H H C O H Are there other acid base reactions in organic chemistry that do not involve H⊕ transfer? + H Cl + ethane thiol pKa = 10.6 CH CH3 H C H S ethanol pKa = 15.9 CH CH3 ethylamine pKa ~ 36 CH CH3 H C H N H H O H O H Cl 3.5 electronegativity 3.0 H H H O + C HH Cl HO H C HH + Cl 17 18 3 9/24/2010 Are there other acid base reactions in organic chemistry that do not involve H⊕ transfer? Choose the answer that has the acid and base correctly identified. A. I = acid, II = acid C. I = base, II = acid B. I = base, II = base D. I = acid, II = base Which species is the acid in the following reaction? E. Neither I or II is an acid or base base acid H H C H H + Cl C H + H H H B H H H B C H H H B C H H C H H 20 H C H H H + H I O C HH Cl HO C HH A B II H H O HH C Cl + 19 H Which species is the acid in the following reaction? Which species is the acid in the following reaction? H H C H C H H H H H B C H C H 21 H H C H H H C H C H H H + H H B H H H B C H H C H H H + H B H H H H B C H H H H B C H H C H H 22 4 ...
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This note was uploaded on 01/07/2011 for the course CHE 321 taught by Professor Fowler/sampson during the Spring '08 term at SUNY Stony Brook.

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