MISCELLANEOUS PROBLEMS

QUESTION 1: Which of the following is NOT true for enantiomers:

1. have the same boiling point.
2. have the same melting point.
3. have the same chemical reactivity with achiral chemical reagents.
4. have the same chemical reactivity with chiral chemical reagents.
5. have the same density.
6. have the same chiroptical properties.

ANSWER:

• (a): true;
• (b): true;
• (c): true;
• (d): false;
• (e): true;
• (f): false;

QUESTION 2: The molecule of cyclohexane hexaol shown below undergoes slow interconversion between two conformational isomers. Draw both conformations and estimate the equilibrium constant.

ANSWER: The conformers are identical.

Since the conformers are identical, they have equal energy.

QUESTION 3: Phosphate derivatives of the molecule below(inositol) are important cellular second messengers. Show substitution of which hydroxyl groups will bring about formation of chiral phosphate esters.

ANSWER:

QUESTION 4: What is the hybridization of heteroatoms in the following compounds:

1. Trimethylamine nitrogen.
2. Acetaldehyde oxygen.
3. Acetone oxime nitrogen.
4. ester group bridging oxygen atom.
5. Oxirane.
6. Phosphorus atom in the phosphate group.

ANSWER:

QUESTION 5: Which of the following statements are TRUE?

1. The chair conformation of cyclohexane is the most stable one.
2. The most stable conformation of butane has methyl groups in synclinal arrangement.
3. Conformational equilibrium is decided by the free energy of each conformer.
4. Conformers can be distinguished by physical methods such as boiling point.
5. The reason for different biological activity of enantiomers is that only one of them binds to all receptor sites.
6. In-plane rotation of the Fisher projection by 90^o is equivalent to mirror plane reflection.
7. Rotation by 90^o of any compound is equivalent to mirror reflection.
8. The precedence rules can be used to determine E/Z -configuration of ring compounds.
9. The D-prefix means the compound rotates plan of polarized light to the right.
10. d-Prefix means the compound has the same configuration as d-glyceraldehyde.
11. Diastereomers can be distinguished by their melting point or other physical properties.

ANSWER:

1. True.
2. False.
3. True.
4. False.
5. True.
6. True.
7. False.
8. True.
9. False.
10. False.
11. True.