Whittier College
Organic Chemistry: CHEM 231A
Practice Problem Set #5
1. Predict whether the following reactions will occur as drawn. Propose a proper product for the reaction if
it does not occur as drawn. Explain your rationale:
1a.
1b.
1c.
Mg Br
Et2O
OH
H
O
HO
Br
NaH / Et2OO
1. mCPBA
2.H2SO4 / isopropanolO
HO
2. The reaction of (2R) 2-phenyl-2-bromopropane in aqueous ethanol at 50 C gives a mixture of products.
When the experiment is repeated in the presence of 0.01M LiCl, some 2-chloro-2-phenyl propane is
formed. In subsequent reactions, as the concentration of LiCl is increased, more and more 2-chloro-2-
phenyl propane is formed at the expense of the other products. Throughout this series of experiments,
the rate of disappearance of (2R) 2-phenyl-2-bromopropane, -d[RBr]/dt, is unchanged.
2a. What products are formed before the addition of LiCl?
2b. What is the optical rotation of the entire mixture of products? Explain briefly.
2c. How can the products change when the rate does not change?
2d. Draw a mechanism or several mechanisms that explain these results.
3. If (4R) 4-isopropyl-1-methyl-1-cyclohexene is reacted with meta-chloro perbenzo ic acid (mCPBA), two
compounds are observed via GC-MS, both having a mass spectrum with the highest mass peak at 154
m/z and very similar NMR (Compounds A & B). If the resultant mixture of compounds A & B are
reacted ethyl magnesium bromide followed by aqueous workup, two new compounds are observed via
GC-MS, both having a mass spectrum with the highest mass peak at 184 m/z and both have very similar
NMR (compounds C & D). The resultant mixture of compounds C & D are reacted with trifluoromethyl
sulfonyl chloride and pyridine, two new compounds are formed, compound E &F. These two
compounds were separated using chromatography and characterized. Both had very similar NMR and
Mass Spectra (highest mass = 284 m/z). When each compound is reacted with t-butoxide, a new
product is formed, Compound G & H, respectively. Each are very similar by NMR and GC-MS
(highest mass = 166 m/z). However, it is noted that compound E reacts substantially slower than
compound F.
3a. What are the identities of each product (A – H)?
3b. Why is there a different rate for the reaction of E & F? Use mechanisms, transition states and energy
diagrams to help explain your answer.
3c. What is the optical purity of each product (A – H)? Explain briefly.