EXAM I

Problem 1 (total 20 points, each question worth 2 points)

Which of the following statements are true (write "true or "false", as applicable, in front of the question on the same line):

1. Compounds with multiple chiral centers are chiral.
2. Compounds with a 2-fold axis of symmetry are achiral.
3. Fisher projection of displays the same molecule after its rotation in the plane of projection by 90^o.
4. The cis/trans prefixes refer to configuration.
5. The d or l prefixes refer to configuration.
6. Tertiary amines with three different ligands and an electron pair as a fourth ligand are chiral.
7. meso-compounds are achiral because of center of symmetry.
8. Molecules which are nonsuperimposable mirror images of each other are always enatiomers.
9. threo/erythro prefixes refer to diastereomers.
10. R/S nomenclature shows precise relative location of four ligands of the tetrahedral center in 3D-space.

Problem 2 (total 20 points, 4 points each)

1. List all symmetry elements (n-fold axis, a plane, or a center of symmetry) of the structures shown below.
2. Draw where approximately in the structure the element may be applied.
3. State in what relation it is to the structure (e.g. in plane of the structure, vertical in plane of projection, horizontal perpendicular to the plane of projection, etc.).
4. State which compounds are chiral, and identify each chiral center by an asterisk (*).

Problem 3

PART I Designate the RS configurations of each chiral centers in the structures shown below (12 points, 3 for each chiral center). Be sure to label each ligand of the chiral carbon atoms with the appropriate precedence numbers (from 1 to 4). If two chiral centers share the same ligand, redraw the structure to show separately precedence at each center.

PART II Draw the Fisher projection of 2Z,4S- 4-bromopentene-2 (10 pts).

Problem 4

Part I(12 pts, 3 each) Define the relation of each of the the structures B through E to the structure A shown below as:

• Identity (ID);
• Enantiomers (ENT);
• Diastereomers (DIA);
• Constitutional isomers(CON);

PART II Choose a meso-structure (or structures) from the following (8 pts):

Problem 5

The free energy difference between the synclinal and antiperiplanar conformers of meso-2,3-dibromobutane is =-2.5 kcal/mol.

PART I Show Newman projection of all three staggered conformers and name each of them (6 pt).

PART II Explain how you would determine molar fractions of each conformer in the equilibrium mixture. For full credit show the appropriate equations, and step by step problem solving. You need not give numerical values of molar fractions (14 pt).