Colorado State University Organic Chemistry Stereocenter Questions

P R O B L E M 6.1
Each of the following molecules has one stereocenter:
• (a)
•
(b)
•
(c)
•
(d)
Identify the stereocenter in each and draw stereorepresentations of the enantiomers of each.
P R O B L E M 6.2
Assign an R or S configuration to each stereocenter:
(a)
(b)
(c)
(d)
P R O B L E M 6.3
Following are stereorepresentations of the four stereoisomers of 3-chloro-2-butanol:
(a)
Which compounds are enantiomers?
(b)
Which compounds are diastereomers?
P R O B L E M 6.4
Following are four Newman projection formulas for tartaric acid:
(a)
Which represent the same compound?
(b)
Which represent enantiomers?
(c)
Which represent(s) meso-tartaric acid?
(d)
Which are diastereomers?
P R O B L E M 6.5
How many stereoisomers exist for 1,3-cyclopentanediol?
P R O B L E M 6.6
How many stereoisomers exist for 1,4-cyclohexanediol?
6.7
Define the term stereoisomer. Name four types of stereoisomers.
6.8
In what way are constitutional isomers different from stereoisomers? In what way are they the same?
6.9
Compare and contrast the meaning of the terms conformation and configuration.
6.10
Which of these objects are chiral (assume that there is no label or other identifying mark)?
(a)
A pair of scissors
(b)
A tennis ball
(c)
A paper clip
(d)
A beaker
(e)
The swirl created in water as it drains out of a sink or bathtub
6.14
One reason we can be sure that sp3 hybridized carbon atoms are tetrahedral is the number of
stereoisomers that can exist for different organic compounds.
(a)
How many stereoisomers are possible for CHCl3, CH2Cl2, and CHBrClF if the four bonds to carbon have a
tetrahedral geometry?
(b)
How many stereoisomers are possible for each of the compounds if the four bonds to the carbon have a
square planar geometry?
SECTION 6.2 Enantiomers
6.15
Which compounds contain stereocenters? (See Example 6.1)
• (a)
2-Chloropentane
•
(b)
3-Chloropentane
•
(c)
3-Chloro-1-pentene
•
(d)
1,2-Dichloropropane
6.17
Which alcohols with the molecular formula C5H12O are chiral?
6.18
Which carboxylic acids with the molecular formula C6H12O2 are chiral?
6.19
Draw the enantiomer for each molecule: (See Example 6.1)
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l)
6.20
Mark each stereocenter in these molecules with an asterisk (note that not all contain
stereocenters): (See Example 6.1)
(a)
(b)
(c)
(d)
6.21
Mark each stereocenter in these molecules with an asterisk (note that not all contain
stereocenters): (See Example 6.1)
(a)
(b)
(c)
(d)
6.22
Mark each stereocenter in these molecules with an asterisk (note that not all contain
stereocenters): (See Example 6.1)
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(CH3)3CCH2CH(OH)CH3
6.23
Following are eight stereorepresentations of lactic acid: (See Examples 6.3, 6.4)
•
(a)
•
(b)
•
(c)
•
(d)
•
(e)
•
(f)
•
(g)
•
(h)
Take (a) as a reference structure. Which stereorepresentations are identical with (a) and which are
mirror images of (a)?
6.25
Which molecules have R configurations? (See Example 6.2)
• (a)
•
(b)
•
(c)
•
(d)
6.26
Following are structural formulas for the enantiomers of carvone: (See Example 6.2)
Each enantiomer has a distinctive odor characteristic of the source from which it can be isolated. Assign
an R or S configuration to the stereocenter in each. How can they have such different properties when
they are so similar in structure?
6.29
For centuries, Chinese herbal medicine has used extracts of Ephedra sinica to treat asthma. Investigation
of this plant resulted in the isolation of ephedrine, a potent dilator of the air passages of the lungs. The
naturally occurring stereoisomer is levorotatory and has the following structure: (See Example 6.2)
Assign an R or S configuration to each stereocenter.
: (See Example 6.2)
6.32
Label the four stereocenters in amoxicillin, which belongs to the family of semisynthetic penicillins:
6.33
Label all stereocenters in loratadine (Claritin®) and fexofenadine (Allegra®), now the top-selling
antihistamines in the United States. Tell how many stereoisomers are possible for each. (See
Examples 6.5, 6.6)
(a)
(b)
How many stereoisomers are possible for each compound?