316 Chem Problem Set 4 1. For the molecular formula C6H11N: a. calculate the units of unsaturation: b. list the possible combinations of pi bonds and rings that could make up the units of unsaturation found in part (a) and draw an isomer to represent each combination. 2. Draw the two compounds with the formula CH3CH=NCH3. 3. For the following molecules, draw and label the cis and trans isomers. If geometric isomers cannot exist, write "no cis or trans".
Br
(CH3)3CCHCH(CH3 )2
Br H3CHC CHI CHCH3
4. Draw the various eclipsed and staggered conformations for the following alkane. Label each conformer as "totally eclipsed," "eclipsed," guache," and "anti." Graph the relative energy of each conformer.
draw the Newman projection looking down this bond
5. 1,2-dichloroethane is shown below:
Cl Cl
a. Draw the various eclipsed and staggered conformations of 1,2-dichloroethane using Newman projections. Label each conformation as "totally eclipsed," "eclipsed," "gauche," and "anti." b. Graph the relative energy of each conformation. (Assume that 0 is the totally eclipsed conformation). c. 1,2-dichloroethane has two polar bonds. From your drawings of the conformations of this compound, determine which conformation maximizes the molecular dipole moment and which conformation minimizes the molecular dipole moment. Draw those conformations as Newman projections. Briefly explain how the relative energy of these two conformations is affected by their dipole moments (as compared to a simple alkane).
6. The aldehyde-alcohol shown below is a member of an important class of compounds called "aldols."
O H OH
draw Newman projections looking down this bond
a. It is known for aldol products that one conformation is significantly more stable than the others. The most stable conformation is NOT the anti even conformer, though the anti conformer would be more stable based on steric hindrance. Carefully analyze this compound and determine which conformer is the most stable. It will help you to draw Newman projections along the bond indicated in the structure below. Be sure to indicate which conformer is the most stable! b. Now that you have selected the right conformer, give a brief explanation as to why an aldol product would behave differently than most other compounds. 7. Draw the most and least stable chair conformations of the following molecules:
D OH Cl cis cis trans (D=deuterium)
8. Starting with the structure below, draw its enantiomer, a diastereomer, and a conformer.
Br CH3
9. Circle the chiral centers. Calculate the maximum number of configurational isomers for each.
a. HO OH glyceraldehyde d. O O H limonene O OH e. HO CH3 N(CH3 )2 OH NH2 OH O HO HO O O b. c. menthol OH
O cortisone
tetracycline
10. Indicate whether these pairs are enantiomers, diastereomers, or the same:
a. H Cl Br H H Br H Cl b. O c. O
HO O
OH
HO O
OH
HO
OH
HO
OH
11. One of the major triumphs in organic chemistry in the late 1800's was the synthesis and characterization of all the possible stereoisomers of the six-carbon sugars, as represented by Structure A:
OH HOCH 2 CH
OH CH
OH CH
OH CH
O CH Structure A
a. how many chiral centers does Structure A have? b. what is the maximum number of configurational isomers possible with this number of chiral centers? c. how many meso structures would be present among the configurational isomers of Structure A? d. in analyzing a mixture of all possible configurational isomers of structure A by gas chromatography or thin-layer chromatography (without a coating of a chiral material), how many different peaks or spots could you expect to see? In other words, how many compounds or sets of compounds would have different physical properties?