EXAM II

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. All compounds which have carbon atom with four different ligands are chiral.
2. Enantiomers are stereoisomers of a chiral compound.
3. Enantiomers of the same compound have different physical properties.
4. Tereoisomers with different configurations are enantiomers.
5. Diastereomers are compounds of the same constitution, but not related through the mirror reflection operation.
6. Meso-compounds have chiral carbon atoms and are therefore chiral.
7. Compounds which only have an axis of symmetry are always chiral.
8. cis- and trans-isomers are diastereomers.
9. All structures which are related to each other as an object to its mirror image are enantiomers.
10. The d-prefix means the compound has the same configuration as d-glyceraldehyde.

Problem 2 (total 20 points, 4 points each)

1. List 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. If no symmetry is detected, state "NONE", however, in such case identify the 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 2S,3R-dibromobutane (10 pts).

Problem 4

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

• identical (ID);
• enantiomeric (ENT);
• diastereomeric (DIA);

Part II: (8 points total, 2 for each problem). Which of the four pairs of the structures shown below are:

• identical (ID);
• enantiomeric (ENT);
• diastereomeric (DIA);
• constitutional isomers (CON);

Problem 5

Define which of the conformations in each row shown below is more stable (18 points, 6 points for each problem).

Score for exam II: _______/100