Chem&219 Unit 3, Organic Chemistry Module 3, Final Exam CHEM 219, CHEM 219 EXAM 1 with 100% correct answers
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Stereochemistry
the study of the three-dimensional structure of molecules
Stereoisomers
Compounds with the same structural formula and connectivity but with a different 3D arrangement of the atoms in space.
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Chem&219 Unit 3, Organic
Chemistry Module 3, Final
Exam CHEM 219, CHEM 219
EXAM 1 with 100% correct
answers
Stereochemistry - answer the study of the three-dimensional
structure of molecules
Stereoisomers - answer Compounds with the same structural
formula and connectivity but with a different 3D arrangement of the
atoms in space.
Enantiomers - answer Stereoisomers that that are non-
superimposable mirror images. Enantiomers have the same
connectivity but different orientations (twist) of the four atoms or
groups in 3D space.
The two different forms of the chiral molecule (the "left-handed"
form or a "right-handed" forms)
How do the differences caused by steroisomers differ than the
differences caused by constitutional isomers. - answer While the
structural differences between stereoisomers are more subtle than
those between constitutional isomers, stereoisomerism is often
responsible for significant differences in the chemical and physical
properties of organic compounds, including the biochemical
behavior of many compounds such as drug molecules, amino acids,
carbohydrates, and nucleic acids. Several of the human senses,
especially smell, are greatly affected by stereoisomerism in organic
compounds.
,cis-stereoisomers - answer have the substituents on the same
side/face of the ring or double bond
trans-stereoisomers - answer have the substituents on opposite
sides/faces of the ring or double bond
Chirality - answer the concept of "handedness" in an object.
Consider the difference between a pair of socks and a pair of gloves.
A sock can be worn (interchangeably) on either the left or right foot,
but the same is not true for the gloves. A left-handed glove cannot
be worn on the right hand and vice-versa. The gloves possess the
property of "handedness" (chirality)
Observation will reveal that chiral objects are typically not
symmetrical (asymmetric), while achiral objects typically exhibit
multiple planes of symmetry within the object itself.
chiral - answer a molecule that is not superimposable on its mirror
image (possesses the property of handedness)
achiral - answer A molecule that is superimposable on its mirror
image (does not possess the property of handedness)
What test can be applied to determine if an object is chiral or
achiral? - answer A simple test involves comparing the object and its
mirror image for superimposability.
Superimposability - answer The ability to align (overlap) two objects
so that every unique part of each is in direct alignment with the
same unique part on the other.
,What does it mean when a molecule is a chiral molecule? - answer
An organic compound that can exist as two different forms ("left-
handed" form or a "right-handed" form)
Is lactic acid structure chiral or achiral? - answer 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.
Is the molecule 2-chloropropane chiral or achiral? - answer 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.
What is the most common cause of chirality in an organic molecule?
- answer The presence of a tetrahedral stereocenter.
Identifying a stereocenter in an organic molecule is a way to quickly
determine if an organic molecule may possess the property of
chirality.
, stereocenter - answer A carbon atom with tetrahedral geometry
that is bonded to four DIFFERENT atoms or groups (4 single bonds
connected to four different atoms or groups).
This type of carbon is known as a stereocenter, a stereogenic center,
or a chiral center.
A chiral molecule will almost always possess one (or more)
stereocenters. In contrast, most molecules without a stereocenter
are not chiral.
Stereocenter vs Chirality - answer The stereocenter is the cause of
the chirality, while chirality is a property of the molecule as a whole.
What are two things that rule out a carbon from being a
stereocenter? - answer - 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)
How is the presence of a stereocenter in an organic structure is
denoted? - answer With an asterisk next to the stereogenic carbon
Look at the image of 3-methylhexane and explain whether it has a
stereocenter and why? - answer Yes, it is chiral because it has a
stereocenter. The substituents attached to carbon #3 are a methyl,
an ethyl, a propyl, and a lone hydrogen (not pictured). While
methyl, ethyl, and propyl are all carbon-based and very similar, they
are not identical and that creates a stereocenter.
Look up an image of 1-bromo-2-iodopropane and explain whether it
has a stereocenter and why? - answer 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
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