236 CHAPTER 5 Stereochemistry
- The enantiomers of 1,2-dimethylaziridine can be separated even though one of the “groups”attached to nitrogen is a lone pair.
Explain. - Of the possible monobromination products shown for the following reaction, circle any that would not be formed.
- A sample of (S)- -lactic acid was found to have an optical purity of 72%. How much Risomer is present in the sample?
- Is the following compound optically active?
- Give the products of the following reactions and their configurations:
- a. Using the wedge-and-dash notation, draw the nine stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane.
b. From the nine stereoisomers, identify one pair of enantiomers.
c. Draw the most stable conformation of the most stable stereoisomer. - Sherry O. Eismer decided that the configuration of the asymmetric carbons in a sugar such as D-glucose could be determined
rapidly by simply assigning the Rconfiguration to an asymmetric carbon with an OH group on the right and the Sconfiguration to
an asymmetric carbon with an OH group on the left. Is she correct? (We will see in Chapter 22 that the “D”in D-glucose means the
OH group on the bottommost asymmetric carbon is on the right.) - Cyclohexene exists only in the cis form, while cyclodecene exists in both the cis and trans forms. Explain. (Hint:Molecular
models are helpful for this problem.) - When fumarate reacts with in the presence of the enzyme fumarase, only one isomer of the product is formed. Its structure is
shown. Is the enzyme catalyzing a syn or an anti addition of
+ D 2 O−OOCΗ
fumarateCOO−fumarase COO−COO−DO H
DHH
CCD 2 O?D 2 OD-glucoseCH 2 OHHOH
HO H
HOH
HOHHC OH CH 3H 3 C CH(CH 3 ) 2HBrHBr
peroxideH^2
PtBr 2 , CH 3 OHH+, H^2 OBr 2 , CH 2 Cl 2Br 2 , H
2 O(^1). BH
2. H^3 /THF
2 O 2 , HO−
C C
H
Cl Cl
Br
Br
H H
H
(+)
CH 2
CH 3
H Br + Br 2 + HBr
300 °C
CH 2 CH 3
CH 3
Br H
HBr
CH 2 CH 3
CH 3
Br H
HBr
CH 2 CH 3
CH 3
HBr
HBr
CH 2 CH 3
N
H H
enantiomers of 1,2-dimethylaziridine
CH 3
CH 3
N
CH 3
CH 3