Out of 20 pts. Key Problem Set #5, 5.12 Spring 2003 Due Monday, March 31, 4pm 1. a) Rank the following series of molecules based on reactivity in an S_N2 reaction (NaI/acetone). (1=fastest S_N2, 4= slowest S_N2) Me Me Me Me Me Me Me Me \ / / \ / \ / \ / \ / \ OTI Me Cl Me Cl Me Br Me / \ / \ / \ / \ / \ / \ / \ Me Me Me Me Me Me Me Me 1 4 3 2 b) Rank the following series of molecules based on reactivity in an S_N1 reaction (EtOH/heat). (1= fastest S_N1, 4= slowest S_N1) Me Br Br Br OMe Br Br Br \ / / \ / \ / \ / \ / \ Me Me Me Me Me Me Me Me / \ / \ / \ / \ / \ / \ / \ Me Me Me Me Me Me Me Me 2 3 1 4 c) Rank the following series of molecules based on reactivity in an E2 reaction (NaO/Pr/PrOH). (1= fastest E2, 4= slowest E2) Br Br Br Br Me Br Br Br \ / / \ / \ / \ / \ / \ Me Me Me Me Me Me Me Me / \ / \ / \ / \ / \ / \ / \ Br Br Br Br Me Br Br Br 1 4 2 3 locked axial no a.p.p. Hs (A_eq = 1.74) + (A_irr = 2.1) 3pts 23 3 pts. 2. a) Predict the product of the following reaction, and provide the mechanism for its formation. Me Br K+O-tBu \ / / \ Me Me H / \ / \ H Ph Br (E2) H \ Ph / \ H Ph (antiperiplanar) b) Draw a picture of the transition state for the above reaction. Pay attention to stereochemistry! H Br- \ / C C / \ / \ H Ph H c) If the same molecule were heated in diisopropylamine (Pr₂NH), would you expect the same product that you drew in part a? Why or why not? No! Heating the molecule from part a in diisopropylamine would result in E1 elimination. Because E1 eliminations go through a planar carbocation, both alkene isomers can form. In general, the most stable isomer results from an E1 elimination. (Phenyl on the same side as the methyl, not the isopropyl.) H \ Ph / \ H Ph BAD! H \ Ph / \ H Ph (major) 3 pts. 3. Predict the products of the following substitution reactions, and specify whether each proceeds by S_N1 or S_N2. Pay attention to stereochemistry. a) Cl \ Me / \ Me Me MeOH → OH \ Me / \ Me Me OH / Me / \ Me Me (enantiomers) SN1 b) Me OMe \ / Me Me / \ / \ Me Me Me Me KCN → CN \ Me / \ Me Me OMe \ Me / \ Me Me DMF SN2 c) F \ Cl / \ Me Me NaI → F \ I / \ Me Me acetone, Δ SN2 d) Cl \ Me / \ Me Br H₂O → OH \ Me / \ Me Me SN1