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I n 3 n 3 i a the sn2 reactivity with

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I N 3 - + N 3 + I - (a) The SN2 reactivity with cyclohexyliodide occurs predominantly through one of the two limiting conformations. Carefully analyze a model and provide a detailed mechanism of the iodide displacement starting with cyclohexyliodide in its most stable conformation. I H (b) Carefully draw a structure of the transition state. (c) Write out the rate law for this proposed reaction assuming a rate limiting SN2 attack mechanism. 7. Consider the eight structural isomers of C 5 H 11 Br (A-H). Treatment of these 8 isomers with NaCN in DMF follows second order kinetics and shows the following relative rates for product formation: A ~ B > C > D ~ E > F >> G and H does not react under these conditions Compounds C, D and F have configurational stereoisomers. The substitution of D and F with NaCN inverts the configuration at the carbon center to which the CN attaches, while treatment of C proceeds with retention of configuration. Draw the structure of each isomer in the box below. In case of stereocenters, draw the S absolute configuration. E G A B C D F H Chem 33, Kanan & Stack, 2012, PS 6; pg 5
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(g) If the concentration of azide ( A ) is increased 10-fold to 0.1 M at parity of all other conditions in part d, calculate the initial rate of disappearance of cyclohexyliodide. Explain why the initial rate is greater than in part d. (h) The conditions in part g, in which one reagent is significantly larger than the other (~10 fold larger), leads to conditions referred to as pseudo-first-order. As the concentration of chloride ( A ) does not significantly change over the course of the reaction (is constant), its concentration can be integrated into the rate constant of the reaction. initial reaction rate = k [ A ] 1 [ B ] 1 = k' [ B ] 1 if [ A ] >> [ B ] and k` = k [ A ] With a first-order reaction, a half-life of the reaction (t 1/2 ) is equal to: t 1/2 = ln 2 / k ~ 0.7 / k A half-life is the time needed to convert one half of the starting material to product. With a first-order reaction, 5 half- lives assure > 95% completion of the reaction.
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