CHE 230 Practice Problems 1
1.
Draw the structures of the following compounds. Be sure to indicate the relevant
stereochemistry.
S –1-Bromo-1-chloroethane.
Br
Br
Cl
Cl
CH3
H
CH3
R-2-butanol
OH
2.
Draw the molecular formula for an unsaturated alkyl chloride (C5H9Cl) that shows
a) neither optical activity or E,Z isomerism
Cl
b) both optical activity and E, Z – isomerism
Cl
c) E, Z, isomerism but not optical activity
Cl
d) optical activity but not E, Z isomerism.
Cl
.
Draw all of the stereoisomers of 2,3-butandiol. Label meso compounds and pairs of
enantiomers.
OH
OH
OH
OH
OH
OH
Enantiomers
OH
Meso
OH
4.
What is the relationship between the structures in each pair? Are they the same
compounds, drawn from different perspectives? Are they conformational isomers? Are
they enantiomers? Are they diastereomers? Are they enantiomers drawn in different
conformations?
Enantiomers.
In planar projections these are:
Same Compound (drawn from different sides)
Enantiomers (enantiomers of trans-1,2-diethylcyclohexane, drawn in different
conformations)
O
Br
OCH3
O
Br
Diastereomers (differ at 2 of 3 stereogenic centers)
OCH3
5.
How many stereoisomers are there of the allylic alcohol below? (think carefully about
the meaning of the term “stereoisomer”)
OH
CH2CH3
There are 2 stereogenic centers, so there are 4 possible stereoisomers based on R,S
differences. However, there is also a C=C bond, and there is the possiblility of an E and a
Z isomer of each of the 4 R,S – based stereoisomers. This leads to a total of 8 possible
stereoisomers.
E,R,R
Z,R,R
E,R,S
Z,R,S
E,S,R
Z,S,R
E,S,S
Z,S,S
How about for adamantanol?
OH
There are only 2 stereoisomers (enantiomers).