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Problem_set_10 - temperature and identify its location...

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Problem set 10, Chem. 127/227; Fall quarter 2007 1. Try the following problems from your textbook: Chapter 8, number 15 (hint – think about using 18 O labeled water), and numbers 19, 20, 22 (focus only upon the use of KIEs). 2. (a) Determine whether a conrotatory or a disrotatory motion accounts for the stereochemical outcomes portrayed below. (b) Use the curly arrow formalism to illustrate each process. 3. (a) What is the difference in free energies of activation for competitive kinetically controlled processes wherein the measured product ratio, at T = 25 °C, corresponds to 10 to 1? (b) Suppose that the difference in free energies of activation is 2.8 kcal/mol. Assuming kinetic control and a temperature of 298 K, predict the product ratio. (Hint: You will find it useful to convert from base “e” to base 10, just as we’ve done many times throughout the quarter. In this manner, the calculations become ‘trivial’ and will not require the use of a calculator.) 4. From an examination of the graph shown below, determine (a) whether there is an isokinetic
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Unformatted text preview: temperature and identify its location should it exist, (b) the regions where product A is formed in preference to B , and where the reverse is true. (c) Is the difference in the enthalpies of activation positive or negative? What about the differences in entropies of activation – positive or negative? Provide a reason for your responses. (d) Which product, A or B , is kinetically preferred based solely upon the differences in entropies of activation? Explain. (e) Which is kinetically preferred based solely upon the differences in enthalpies of activation? Explain. (f) Is the prediction based upon enthalpic considerations in agreement or opposite to the prediction based upon entropic considerations alone? 1/T ln(A/B) 5. Write, by inspection, an expression for the rate of formation of B , assuming that a steady state analysis can be performed on the intermediate, I . The symbols R and C refer to reagents. A + R k 1 k 2 I C k 3 B...
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