1) Draw 3D (sawhorse) and Fischer projections for (2R, 3S) - 2-bromo-3-methylpentane (1). Name the

enantiomer of this compound. Name the diastereomers of compound 1.

2) Structure 1 (C₂₇H₄₆O) represents the absolute stereochemistry of cholesterol. There are 2⁸ non-geometric

(2⁹ including the double bond) stereoisomers of cholesterol, one of which is its enantiomer. Assign R,S

configurations to each of the stereogenic centers in 1.

3) Two enantiomers of equal and opposite rotation ([a]_D = 160^o) are inadvertently mixed in the laboratory.

The rotation of the mixture shows [a]_D= -96^o. What is the optical purity of the mixture? What % of each

enantiomer is present in the mixture?

4) A partially racemized compound ( [a]_D= 48^o) is analyzed by chromatography using a chiral support and is

shown to be a 2:3 mixture. Why is this technique possible? What is the rotation of the pure enantiomers?

Which one is the minor isomer? What is the ee?

5) Two chemists measure the specific rotation of an organic compound. He measures a rotation of [a]_D= 0^o

while she obtains a non-zero value? What happened? How can the discrepancy be resolved?

6) When an optically active compound A, C₈H₁₂, is hydrogenated in the presence of a catalyst, cis and trans-

1,4-dimethylcyclohexane are formed. How many molar equivalents of hydrogen are absorbed in this

reaction? What structures are possible for A? Which ones are not possible? What other piece of

information is not known about A?

7) An optically active compound A has the formula C₅H₁₁Br. How many degrees of unsaturation are present?

(See Degrees of Unsaturation in the Study Aids.). A reacts with (n-C₄H₉)₃SnH, a reducing agent, to give

B, C₅H₁₂, and (n-C₄H₉)₃SnBr. Is B optically active? Is there sufficient information here to deduce the

structures of A and B (not the absolute stereochemistry of A)? If so, what are the structures of A and B;

if not, what structures fit A and B? Write a generic (RBr) mechanism for the reduction. [Check alkyl halides in ORGO]