CHEM 219 Final Exam (2026) – Principles of
Organic Chemistry Portage Learning
Verified Qs & Ans for A+ Grade
Stereochemistry - answers the study of the three-dimensional structure of molecules
Stereoisomers - answers Compounds with the same structural formula and connectivity
but with a different 3D arrangement of the atoms in space.
Enantiomers - answers 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. - answers 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 - answers have the substituents on the same side/face of the ring or
double bond
trans-stereoisomers - answers have the substituents on opposite sides/faces of the ring
or double bond
Chirality - answers 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 - answers a molecule that is not superimposable on its mirror image (possesses
the property of handedness)
achiral - answers 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? - answers A
simple test involves comparing the object and its mirror image for superimposability.
Superimposability - answers 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? - answers 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? - answers 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? - answers 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? - answers 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 - answers 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 - answers 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? - answers - 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? - answers
With an asterisk next to the stereogenic carbon
Look at the image of 3-methylhexane and explain whether it has a stereocenter and
why? - answers 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? - answers 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 cyclohex-2-ene-1-ol and explain whether it has a stereocenter and
why? - answers Yes it does have a stereo center on carbon #1. In the molecule
cyclohex-2-ene-1-ol, stereocenters can exist in cyclic structures as well. The #1 carbon
in this molecule is a stereocenter because there is a difference in connectivity (different
groups) as we go counterclockwise vs clockwise around the ring from the number one
carbon.
How does the chirality of ibProfin impact the effects of the drug? - answers When
ibuprofen is synthesized, the two enantiomeric forms are produced in equal amounts, so
you ingest both enantiomers. Only one of the enantiomeric forms is active at relieving
pain and the other is inactive. The non-active enantiomer is slowly converted by
enzymatic processes in the body to the active form, allowing for an fast and slow effects
of the drug.
How does the chirality of Thalidomide impact the effects of the drug? - answers One of
the enantiomers is therapeutic (treats nausea symptoms) and one of the enantiomers is
toxic/has other harmful effects. Thalidomide was given to pregnant women in the late
, 1950's and early 1960's as a treatment for nausea. While one of the enantiomeric forms
was active as a therapeutic, it was not known that the other form caused severe birth
defects (teratogenic) in many of the children born to mothers who used the drug.
Thalidomide was removed from the market for pregnant women shortly after this
discovery.
Many of the human senses are subject to the influence of chirality, which sense in
particular is sensitive to chirality? - answers Our sense of smell
Describe the ways humans can sense the different enantiomers of the Carvone
compound? - answers Carvone (a molecule with one stereocenter) forms two mirror-
image forms or enantiomers. One form has a sweetish, minty smell, like spearmint
leaves. Its mirror image has a spicy aroma with notes of rye, like caraway seeds.
Spearmint leaves and caraway seeds are two of the largest natural sources for the
extraction of the two isomeric forms of carvone.
What does the ability of humans to smell different enantiomers tell about human
bodies? - answers The fact that the two enantiomers are perceived as smelling
differently is evidence that olfactory receptors in the human nose contain chiral groups,
allowing them to respond more strongly to one enantiomer than to the other. Many, but
not all enantiomers have unique and distinguishable odors.
How do different enantiomers behave compared to each other with melting points,
boiling points, density, and refractive index, etc? - answers These physical properties
would be the same between the enantiomers.
While the behavior of enantiomers in biological systems can be quite different, an
interesting note is that the physical properties of pairs of enantiomers are identical.
Why can mixtures of enantiomers of a given compound be very challenging to separate
from one another? - answers Because the physical properties of pairs of enantiomers
are identical (can't boil them to separate etc.)
What device is used to determine the percent composition of an unknown mixture of
enantiomers? - answers A polarimeter
How does a polarimeter work? - answers A polarimeter uses a beam of plane-polarized
light to interact with a sample of a chiral compound of unknown enantiomeric
composition. The chiral molecules cause the plane of the polarization of the beam of
light to rotate. Based on the direction and magnitude of rotation, the % composition
(what % R and % S) of the sample can be determined. The rotation of light by individual
enantiomers is always equal but opposite. Under carefully controlled and standardized
conditions, the measurement of the optical activity of a pure single enantiomer of a
compound gives a value known as the specific rotation.
Organic Chemistry Portage Learning
Verified Qs & Ans for A+ Grade
Stereochemistry - answers the study of the three-dimensional structure of molecules
Stereoisomers - answers Compounds with the same structural formula and connectivity
but with a different 3D arrangement of the atoms in space.
Enantiomers - answers 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. - answers 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 - answers have the substituents on the same side/face of the ring or
double bond
trans-stereoisomers - answers have the substituents on opposite sides/faces of the ring
or double bond
Chirality - answers 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 - answers a molecule that is not superimposable on its mirror image (possesses
the property of handedness)
achiral - answers 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? - answers A
simple test involves comparing the object and its mirror image for superimposability.
Superimposability - answers 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? - answers 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? - answers 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? - answers 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? - answers 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 - answers 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 - answers 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? - answers - 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? - answers
With an asterisk next to the stereogenic carbon
Look at the image of 3-methylhexane and explain whether it has a stereocenter and
why? - answers 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? - answers 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 cyclohex-2-ene-1-ol and explain whether it has a stereocenter and
why? - answers Yes it does have a stereo center on carbon #1. In the molecule
cyclohex-2-ene-1-ol, stereocenters can exist in cyclic structures as well. The #1 carbon
in this molecule is a stereocenter because there is a difference in connectivity (different
groups) as we go counterclockwise vs clockwise around the ring from the number one
carbon.
How does the chirality of ibProfin impact the effects of the drug? - answers When
ibuprofen is synthesized, the two enantiomeric forms are produced in equal amounts, so
you ingest both enantiomers. Only one of the enantiomeric forms is active at relieving
pain and the other is inactive. The non-active enantiomer is slowly converted by
enzymatic processes in the body to the active form, allowing for an fast and slow effects
of the drug.
How does the chirality of Thalidomide impact the effects of the drug? - answers One of
the enantiomers is therapeutic (treats nausea symptoms) and one of the enantiomers is
toxic/has other harmful effects. Thalidomide was given to pregnant women in the late
, 1950's and early 1960's as a treatment for nausea. While one of the enantiomeric forms
was active as a therapeutic, it was not known that the other form caused severe birth
defects (teratogenic) in many of the children born to mothers who used the drug.
Thalidomide was removed from the market for pregnant women shortly after this
discovery.
Many of the human senses are subject to the influence of chirality, which sense in
particular is sensitive to chirality? - answers Our sense of smell
Describe the ways humans can sense the different enantiomers of the Carvone
compound? - answers Carvone (a molecule with one stereocenter) forms two mirror-
image forms or enantiomers. One form has a sweetish, minty smell, like spearmint
leaves. Its mirror image has a spicy aroma with notes of rye, like caraway seeds.
Spearmint leaves and caraway seeds are two of the largest natural sources for the
extraction of the two isomeric forms of carvone.
What does the ability of humans to smell different enantiomers tell about human
bodies? - answers The fact that the two enantiomers are perceived as smelling
differently is evidence that olfactory receptors in the human nose contain chiral groups,
allowing them to respond more strongly to one enantiomer than to the other. Many, but
not all enantiomers have unique and distinguishable odors.
How do different enantiomers behave compared to each other with melting points,
boiling points, density, and refractive index, etc? - answers These physical properties
would be the same between the enantiomers.
While the behavior of enantiomers in biological systems can be quite different, an
interesting note is that the physical properties of pairs of enantiomers are identical.
Why can mixtures of enantiomers of a given compound be very challenging to separate
from one another? - answers Because the physical properties of pairs of enantiomers
are identical (can't boil them to separate etc.)
What device is used to determine the percent composition of an unknown mixture of
enantiomers? - answers A polarimeter
How does a polarimeter work? - answers A polarimeter uses a beam of plane-polarized
light to interact with a sample of a chiral compound of unknown enantiomeric
composition. The chiral molecules cause the plane of the polarization of the beam of
light to rotate. Based on the direction and magnitude of rotation, the % composition
(what % R and % S) of the sample can be determined. The rotation of light by individual
enantiomers is always equal but opposite. Under carefully controlled and standardized
conditions, the measurement of the optical activity of a pure single enantiomer of a
compound gives a value known as the specific rotation.
