L2ProblemsFrommidterms - impact, you have to obtain less...

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1 Questions from 2007 MIDTERM EXAM - CHM 4328B 6. Quickies! (18 points) c) Lactones are more reactive than esters: they are significantly more susceptible to nucleophilic attack and deprotonation. Explain briefly. (2 points) e) In one or two sentences, provide a clear explanation of kinetic vs. thermodynamic acidity. (2 points) f) pKa can be linked to equilibrium ratio and to changes in free energy in a system. Assuming a pKa of 3, what will be the equilibrium ratio? What is the difference in Δ G? (2 points) g) Identify the acidic position(s) on the structure below and justify briefly. (2 points) Questions from 2008 MIDTERM EXAM - CHM 4328B 5. Quickies! (27 points) a) Throughout this semester, we will focus on reactions that are clearly thermodynamically favourable. WHY? (2 points) b) Imagine that, a few years from now, you have to develop an asymmetric route to a pharmaceutically active molecule. Given the production scale and to reduce environmental
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Unformatted text preview: impact, you have to obtain less than 5% of the undesired diasteroisomer (which you know will be separated during recrystallization). Please indicate the preference, in kcal/mol, that you have to achieve and specify how (i.e. with which equations) you can obtain this value. (2 points) O H H 2 e) Carbamates, such as the BOC ( t-b utyl o xy c arbonyl) group, are priviledged protecting groups for nitrogen atoms. The popularity of the BOC group is linked to: 1) its electron withdrawing nature, which attenuates the nucleophilicity of the nitrogen; 2) the fact that it can be removed cleanly under acidic conditions; AND 3) the fact that the carbonyl is inert in the presence of various nucleophiles. Using stereoelectronic arguments, please account for this attenuated electrophilicity. (2 points) R N R' O O Me Me Me R NBoc R'...
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This note was uploaded on 01/11/2012 for the course CHM CHM 4328 taught by Professor Andrébeauchemin during the Spring '11 term at University of Ottawa.

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L2ProblemsFrommidterms - impact, you have to obtain less...

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