Spring 2008

Workshop #4

Problem #1
Complete Chemactivity 22 (Part B and Exercises for Part B) – pages 203-205, 208

Problem #2
Use the Observation-Deduction method to derive the unknown structures in each of the problems below. You may use the templates that I handed out in class as a guide.

(a)Compound J has the following molecular formula, C6H12. Reaction with H2O/H2SO4, or with BH3/THF followed by treatment with a basic solution of H2O2, gives the same compound K, C6H14O. Reaction of J with O3 followed by oxidative workup using Zn, CH3COOH, gives only one product L, C3H6O. Propose structures for J, K, and L.

(b)An optically active compound A (C9H11Br) reacts with potassium tert-butoxide in tert-butyl alcohol followed by reaction with NBS in CCl4 and light to give an optically inactive compound B (C9H9Br). Compound B is reacted with NaOH in DMSO to yield compound C (whose spectroscopic data can be accessed from the organic chem. workshop web page). Compound C undergoes hydrogenation over Pd/C catalyst at room temperature to give compound D (formula C9H12O). Give the structures of compounds A, B, C, and D.

(c)M and N are isomers of C4H8.M reacts with H2 in the presence of a catalyst to give a compound with the formula C4H10.N also reacts with H2/catalyst to give a compound with the formula C4H10, different than that obtained from M. Reaction of M with O3, followed by treatment with Zn/H3O+, gives two products, CH2O and C3H6O.N reacts under the same ozonolysis conditions to give one product, C2H4O. When N is heated with a few drops of H2SO4, it is converted into a mixture of N, O, and P alkenes, in which O predominates.N, O, and P are all reduced in the presence of H2/Pd-C to the same alkane. Ozonolysis of O gives one product, C2H4O, the same product obtained from the ozonolysis of N. Ozonolysis of P gives two products, CH2O and C3H6O. This C3H6O compound from P is not the same as the C3H6O compound from M. Propose structures for M, N, O, and P.

(d)Unknown X, C5H9Br, does not react with bromine (Br2) or with dilute KMnO4. Upon treatment with potassium t-butoxide, X gives only one product, Y, C5H8. Unlike X, Y decolorizes bromine to give compound A, C5H8Br2, and changes KMnO4 from purple to brown to give compound B, C5H10O2. Ozonolysis-reduction of Y gives Z, C5H8O2. Propose structures for A, B, X, Y, and Z and name them.

Problem #3
Complete the following two free-radical mediated mechanisms showing the process of allylic/benzylic bromination. Be sure to show the resonance structures for the intermediates that you create in the bold boxes.

Problem #4


Given the following addition reaction and the results shown below:

(a)Provide a complete step-by-step reaction mechanism that demonstrates why C and D are the major products in this reaction.

(b)Compose a short narrative that summarizes the observed regiochemical preference (basically, describe what is happening in your proposed mechanism in part a). If intermediates are involved in your mechanism, be sure to discuss their relative stabilities and show how they can be stabilized by hyperconjugation and/or resonance.

(c)Be sure to discuss how the stereochemical differences arise among all products A thru D (assign R/S configuration where appropriate).

Problem #5

Complete the reactions by providing the structures for A-M with the correct regiochemistry and stereochemistry.