exam4_for_2007

exam4_for_2007 - 4th exam; Chem. 127/227; Fall quarter 2007...

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1 4 th exam; Chem. 127/227; Fall quarter 2007 1. [a] Formulate a mechanism, illustrating each of the steps of the transformation shown below. OH I 2 OH I [b] When 2,4,6-trideuteriophenol is examined, and the relative rates of reaction are measured for phenol and the trideuterio analog, one finds that k H /k D ~ 4. What does this information indicate regarding which of the steps in the mechanism is rate limiting step? 2. Examine the equilibrium shown below. [a] What is the pKa of EtOH, HN(i-Pr) 2 , and a proton positioned alpha to an aldehyde/ketone? [b] Calculate K eq as a function of the base used to achieve deprotonation, the bases being NaOEt and LDA. SHOW YOUR WORK. CHO B + k 1 k –1 CHO + H–B B NaOEt LDA K eq 3. Shown below are the diastereomeric aldol condensation products of butyraldehyde. Suppose that the condensation was conducted at 25 °C, and that the free energy difference between the two structures corresponds to 1.4 kcal/mol. What will be the product ratio if the reaction is carried out at this temperature under the conditions of thermodynamic control? SHOW YOUW WORK. CHO HO CHO HO 4. [a] Write an expression for the rate of formation of the structure shown on the right side of the scheme illustrated below. In so doing, assume that the steady state approximation can be applied to the enolate.
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exam4_for_2007 - 4th exam; Chem. 127/227; Fall quarter 2007...

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