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CHEM 219 UNIT 3 QUESTIONS WITH ANSWERS 100% CORRECT
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Name: Score:49 Multiple choice questions
Definition 1 of 49
a molecule that is not superimposable on its mirror image (possesses the property of
handedness)
Chirality
meso compound
chiral
achiral
Definition 2 of 49
They are diastereomers
If either the cis or the trans stereoisomer was held up to a mirror, the mirror image would be the
same (the mirror image of cis is not trans, and the mirror image of trans is not cis). Thus, since
they are stereoisomers that are not mirror images of one another, cis-trans pairs are
diastereomers.
What is the most common cause of chirality in an organic molecule?
Which word would describe the relationship between cis/trans pairs of molecules?
What does the ability of humans to smell different enantiomers tell about human bodies?
Look up an image of 1-bromo-2-iodopropane and explain whether it has a stereocenter
and why?
,Definition 3 of 49
- if the carbon has more than one hydrogen on it (makes it so there can't be four different
groups/atoms)
- if the carbon has a double or triple bond (makes it so there cant be four separate bonds and
therefore can't have tetrahedral geometry)
What are two things that rule out a carbon from being a stereocenter?
What is the rule when using Fischer projections for moving a projections?
In general why does the 2^n rule for predicting maximum stereoisomers not always
work?
How does the chirality of Thalidomide impact the effects of the drug?
Definition 4 of 49
Attempting to superimpose lactic acid and its mirror image reveals that the two forms cannot
be superimposed, and thus, the molecule is chiral, and it exists as two separate forms known as
enantiomers (Figure 3.4). No matter how one of the structures is rotated, it is impossible to get
all of the atoms/groups in one to align with the same atoms/groups in the mirror image
structure.
stereocenter
Is lactic acid structure chiral or achiral?
How does the chirality of ibProfin impact the effects of the drug?
Is the molecule 2-chloropropane chiral or achiral?
,Definition 5 of 49
Molecules that possess more than one stereocenter become more complex since increasing
the number of stereocenters is associated with increasing numbers of stereoisomeric forms in
which the compound can exist.
With molecules that possess multiple stereocenters, an important skill is to be able to
determine how many stereoisomers will exist for that compound and what the relationships are
(how the individual stereoisomers are related to each other).
Each stereocenter has a pair of enantiomers. So if a compound has two stereocenters there will
be 4 stereoisomers possible.
What does the ability of humans to smell different enantiomers tell about human bodies?
How do the differences caused by steroisomers differ than the differences caused by
constitutional isomers.
What happens to the number of stereoisomers when a molecule has more than one
stereocenter?
Why does the 2^n formula not correctly predict the number of stereoisomers for 2,3-
dichlorobutane?
Definition 6 of 49
Specific rotation is the amount a compound rotates light per concentration of the molecule
and length of the tube through which the light passes.
It is the measurement of the optical activity of a pure single enantiomer of a compound.
The specific rotation is a unique property of each enantiomer that can be used to help identify a
compound, just as with physical constants like melting and boiling points
What makes a meso compound possible?
What is specific rotation?
Is lactic acid structure chiral or achiral?
What does the ability of humans to smell different enantiomers tell about human bodies?
, Definition 7 of 49
When the 3D structure of this molecule is drawn, a tetrahedral geometry is observed around
the central carbon, similar to that of lactic acid. At first glance, it may not be clear that the
molecule is achiral. It is only through the application of the superimposability test that the
molecule reveals its achiral nature.
The absence of a stereocenter is the reason why molecules like 2-chloropropane are achiral.
An analysis of the 3D structure of 2-chloropropane reveals a tetrahedral geometry around the
central carbon but only three different types of atoms or groups attached (there were 4 bonds
to the carbon but 2 of the groups were identical). The symmetrical nature of the 2-
chloropropane molecule comes from having two of the same group on the central carbon -
this allows the structure to be superimposed on its own mirror image, and thus, makes the
molecule achiral.
How does the chirality of Thalidomide impact the effects of the drug?
What makes a meso compound possible?
2-bromo-3-chlorobutane stereoisomers
Is the molecule 2-chloropropane chiral or achiral?
Definition 8 of 49
Yes it does have a stereocenter. Only carbon #2 is a stereocenter because the #1 carbon that
bears the bromine also bears two identical hydrogens (and thus is not a stereocenter). The
presence of the bromine on carbon #1 makes this carbon different from the methyl group
(carbon #3) and thus creates the stereocenter on carbon #2.
Look at the image of 3-methylhexane and explain whether it has a stereocenter and why?
Look up an image of 1-bromo-2-iodopropane and explain whether it has a stereocenter
and why?
What does the ability of humans to smell different enantiomers tell about human bodies?
What happens to the number of stereoisomers when a molecule has more than one
stereocenter?
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