Stereochem

PROBLEMS ON STEREOCHEMISTRY

©2004 OCHeM.com

1. Define the relationship between the following pairs of molecules as identical, non-isomers, conformers, constitutional isomers, enantiomers, ordiastereomers. Circle the molecules that are chiral. Try to develop a system for approaching them in an efficient and effective manner.
A)

CH3 vs. CH3 H3C

CH3

B) Br H vs.

Br

H

C)Br

H H Br

vs.

H

Br Br

H

D)

HO

CH3 vs.

H3 C

H H OH

E)

H Cl

H Cl H OH vs.

H Cl H OH

H CH3 Cl

PROBLEMS ON STEREOCHEMISTRY

©2004 OCHeM.com

2. Supposeyou place a sample in a polarimeter and observe a rotation of 90°. How can you be sure that the sample isn’t rotating the plane polarized light by -270° (both would give the same reading on thepolarimeter!)? Propose a way (either in theory or by experimentation) that you could discern between these possibilities.

3. Provide unambiguous names for the following molecules.
A)

H3 C

Br

B)H

CH3 H Cl CH3

C)

CH3 H H3 C OH H CH2 CH3

PROBLEMS ON STEREOCHEMISTRY

©2004 OCHeM.com

4. Molecule A undergoes an acid-base reaction with sodium hydroxide at the proton connectedto carbon-2. Based on this information, draw the product of this acid-base reaction in the space to the right of the arrow. Then answer the questions that follow:

7

O
1 6

H3 C H
2 3

A5 4

+

Na OH

a) Why is the proton on C-2 more acidic than the protons on C-3, C-4, C-5, and C-7? Explain using words and pictures.

b) As a researcher, you find that molecule A is opticallyactive. You accidentally spill a few drops of sodium hydroxide into the bottle containing A. One week later, you come back to find that the sample of A has completely racemized. Explain thisphenomenon using words and pictures.

PROBLEMS ON STEREOCHEMISTRY

©2004 OCHeM.com

5. Indicate whether each of the following molecules is chiral or achiral. If the molecule is meso, indicate that as...