1. Write structural formulas for all of the constitutionally isomeric compounds having the given molecular formula.^*

A. C₆H₁₄

B. C₅H₁₁Br

C. C₃H₆O

2. A. There are three different constitutional isomers of dichlorocyclopentane. Draw them.

B. There are seven different stereoisomers of dichlorocyclopentane. Draw all of them.

For each isomer, label all stereocenters present as R or S.
Label each structure as chiral or achiral.
Identify any meso compounds.

3. Indicate whether the relationship between each of the following pairs of compounds is enantiomeric, diasteriomeric, or identical.

A.

B.

C.

D.

4. The topic of stereoisomerism is much richer and more interesting than the book makes it out to be. Before tackling this question, I suggest you check out this reference (http://www.science.oregonstate.edu/~gablek/CH334/Chapter5/MesoEtc.htm) that illustrates chiral molecules need not have chiral carbon centers. Remember, chirality is really just a geometric property of an object in which the object is non-superimposable on its mirror image.

With that being said, indicate which of the following molecules are chiral and which are achiral; draw the enantiomers of the chiral molecules. Many of these are difficult to visualize in your mind's eye; these structures are meant to test and grow your spatial reasoning skills. Team up with others, assemble your molecular models and build these structures to justify your choice. These are hard, but you can do it!

5. In 1957, researchers reported the isolation of an optically active compound ([ $α$ ]_D = +40.3^o) from a parasitic fungus. The substance was named cordycepic acid and the structure below was proposed. This structure was later shown to be incorrect. Suggest a reason to be skeptical about the original proposed structure.

INCORRECT structure of cordycepic acid-1.png