MCAT ORGANIC CHEMISTRY EXAM QUESTIONS WITH 100%
CORRECT ANSWERS
What are the four rules for writing resonance structures? -- Correct Answer ✔✔ 1.
_ _ _ _ _ _ _ _ _ _ _ _ _ _
Atoms must not be moved. Only electrons.
_ _ _ _ _ _
2. All resonance atoms must lie in the same plane.
_ _ _ _ _ _ _ _ _
3. Only valid Lewis structures are allowed.
_ _ _ _ _ _
4 . The number of unpaired electrons must remain constant.
_ _ _ _ _ _ _ _ _
What are the two conditions for resonance? -- Correct Answer ✔✔ 1. An atom must
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
have a P orbital or a lone pair of electrons.
_ _ _ _ _ _ _ _ _
2. It must be single bonded to an atom that has a double or triple bond.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
The latter compromise conjugated unsaturated systems.
_ _ _ _ _
Huckel's Rule -- Correct Answer ✔✔ Planar monocyclic rings with (4n+2) Pi-electrons
_ _ _ _ _ _ _ _ _ _ _ _
must be aromatic (have resonance).
_ _ _ _
What is the condition for a chiral center? -- Correct Answer ✔✔ First, the participant
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
in question cannot be a halogen, a CH2 group, an Oxygen, a Halogen, or any Carbon
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
participating in a double or triple bond. _ _ _ _ _ _
Then list the groups attached to a Carbon. They MUST be four different groups. If the
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
conditions are met, then the Carbon in question is a chiral center.
_ _ _ _ _ _ _ _ _ _ _
,How do you determine Absolution Configuration? -- Correct Answer ✔✔ First,
_ _ _ _ _ _ _ _ _ _ _
prioritize the atoms in terms of atomic weights (if two atoms are the same element,
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
then their substituents are compared to determine priority. Substituents on double and
_ _ _ _ _ _ _ _ _ _ _
_triple bonds count 2 and 3 times, respectively). Now, rotate the sigma bond of the
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Carbon so that the lowest priority group faces away. Next, order the numbers in
_ _ _ _ _ _ _ _ _ _ _ _ _ _
terms of increasing priority. If it increases clockwise, then the atom has "S" absolute
_ _ _ _ _ _ _ _ _ _ _ _ _ _
configuration. if it increases counterclockwise, it has "R" absolute configuration. _ _ _ _ _ _ _ _ _
Does absolute configuration determine rotation of plane polarized light? -- Correct
_ _ _ _ _ _ _ _ _ _ _
Answer ✔✔ No _ _
A chiral molecule's mirror image has the _______ absolute configuration -- Correct
_ _ _ _ _ _ _ _ _ _ _ _
Answer ✔✔ Same _ _
What are the conditions of relative configuration? -- Correct Answer ✔✔ The two
_ _ _ _ _ _ _ _ _ _ _ _ _
atoms in question must differ in the attachment of only one substituent, and the
_ _ _ _ _ _ _ _ _ _ _ _ _ _
remaining substituents must be oriented identically relative to the Carbon.
_ _ _ _ _ _ _ _ _
Observed Rotation -- Correct Answer ✔✔ The degree to which compounds rotate
_ _ _ _ _ _ _ _ _ _ _ _
plane polarized light. _ _
How does a polarimeter work? -- Correct Answer ✔✔ A polarimeter screens out all
_ _ _ _ _ _ _ _ _ _ _ _ _ _
but one group of photons that share the same electromagnetic field orientation.
_ _ _ _ _ _ _ _ _ _ _
What is a racemic mixture? -- Correct Answer ✔✔ A mixture of equal stereoisomers
_ _ _ _ _ _ _ _ _ _ _ _ _ _
that yields optically inactive compounds (optically inactive compounds also arise from
_ _ _ _ _ _ _ _ _ _ _
chirality).
If a compound is labeled "+" or "D", what does that mean? -- Correct Answer ✔✔ It
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
rotates plane polarized light to the right. (Dexter = right in Latin)
_ _ _ _ _ _ _ _ _ _ _
If a compound is labeled "-" or "L", what does that mean? -- Correct Answer ✔✔ It
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
rotates plane polarized light to the left. (Laevus = left in Latin)
_ _ _ _ _ _ _ _ _ _ _
,What are the conditions of stereoisomers? -- Correct Answer ✔✔ Molecules with the
_ _ _ _ _ _ _ _ _ _ _ _ _
same molecular formula and bond to bond connectivity, but are not the same
_ _ _ _ _ _ _ _ _ _ _ _ _
compound.
Stereoisomers must be what (exclude geometric isomers from this definition)? -- _ _ _ _ _ _ _ _ _ _ _
Correct Answer ✔✔ They must have a minimum of 1 chiral center in the same
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
relative three dimensional location. _ _ _
Enantiomers are? -- Correct Answer ✔✔ Enantiomers have the same molecular
_ _ _ _ _ _ _ _ _ _ _
formula, the same bond to bond connectivity, are mirror images of one another, but
_ _ _ _ _ _ _ _ _ _ _ _ _ _
are different molecules.
_ _
Optical Purity is? -- Correct Answer ✔✔ The ratio of observed rotation to pure
_ _ _ _ _ _ _ _ _ _ _ _ _ _
sample rotation. _
What is enantiomeric purity? -- Correct Answer ✔✔ The ratio of pure enantiomer to
_ _ _ _ _ _ _ _ _ _ _ _ _ _
racemic mixture. _
Diastereomers -- Correct Answer ✔✔ Same molecular formula, same bond to bond _ _ _ _ _ _ _ _ _ _ _ _
connectivity, not mirror images, not equal molecules. _ _ _ _ _ _
Why do geometric isomers arise? -- Correct Answer ✔✔ Due to a mitigated ability to
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
rotate about a bond, either via ring closure or multiple bonding.
_ _ _ _ _ _ _ _ _ _
List physical property differences between Cis and Trans isomers? -- Correct Answer
_ _ _ _ _ _ _ _ _ _ _ _
✔✔ Cis isomers have a net dipole moment and thus experience a higher boiling point
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
than Trans isomers. However, because a Cis isomer has lower possible permutations
_ _ _ _ _ _ _ _ _ _ _ _
to form a crystal lattice relative to a Trans isomer, Cis isomers do not form crystals as
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_readily.
Higher order alkanes can be differentiated via substituent by the E-Z method.
_ _ _ _ _ _ _ _ _ _ _ _
Elaborate. -- Correct Answer ✔✔ One were to prioritize the substituents on a
_ _ _ _ _ _ _ _ _ _ _ _ _
Carbon. Then, if one were to note that the higher priority substituent exists on
_ _ _ _ _ _ _ _ _ _ _ _ _ _
opposite sides, it gets the E label (Entgegen: German for Opposite). If the higher
_ _ _ _ _ _ _ _ _ _ _ _ _ _
priority substituents are on the same side, it gets the Z label (Zusamen: German for
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Together)
, What is a meso compound? -- Correct Answer ✔✔ Chiral centers that offset one
_ _ _ _ _ _ _ _ _ _ _ _ _ _
another due to symmetry. The net result is an optically inactive compound. In essence,
_ _ _ _ _ _ _ _ _ _ _ _ _ _
meso compounds are actually a chiral. They can be identified by finding a plane of
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
symmetry that divides the compound into two mirror images.
_ _ _ _ _ _ _ _
What is the formula for maximum number of optically active isomers in a single
_ _ _ _ _ _ _ _ _ _ _ _ _ _
compound? -- Correct Answer ✔✔ 2^n, where n is the number of chiral centers.
_ _ _ _ _ _ _ _ _ _ _ _ _
How many functional groups are methyl, primary, secondary, and tertiary alkyl groups
_ _ _ _ _ _ _ _ _ _ _ _
connected to, respectively? -- Correct Answer ✔✔ 0, 1, 2, and 3, respectively.
_ _ _ _ _ _ _ _ _ _ _ _
List some physical properties of alkanes. -- Correct Answer ✔✔ They have low
_ _ _ _ _ _ _ _ _ _ _ _ _
densities. The more molecular weight an alkane has (more Carbon chains), the higher
_ _ _ _ _ _ _ _ _ _ _ _ _
its boiling point due to intermolecular London Dispersion forces. Branching decreases
_ _ _ _ _ _ _ _ _ _ _
the boiling points because the surface area of the molecule is lowered, and the
_ _ _ _ _ _ _ _ _ _ _ _ _ _
molecule cannot form a more relatively polar transient dipole. Unbranches alkanes also
_ _ _ _ _ _ _ _ _ _ _
_exhibit an increase in melting point in molecular weight, but not as predictable as the
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
boiling point of alkanes. _ _ _
What is ring strain? -- Correct Answer ✔✔ The strain caused by a cycloalkane
_ _ _ _ _ _ _ _ _ _ _ _ _ _
deviating from the optimal SP3 109.5 degree angle. Ring strain is usually alleviated by
_ _ _ _ _ _ _ _ _ _ _ _ _ _
the movement of certain bonds away from a flat three dimensional plane.
_ _ _ _ _ _ _ _ _ _ _
List the relative stabilities of cyclohexane conformers when undergoing a ring flip. --
_ _ _ _ _ _ _ _ _ _ _ _ _
Correct Answer ✔✔ Chair (low) _ _ _ _
Half Chair (highest)
_ _
Twist (lower than Half Chair)
_ _ _ _
Boat (higher than twist but lower than Half Chair)
_ _ _ _ _ _ _ _
Twist of the other side _ _ _ _
Half chair of the other side
_ _ _ _ _
Chair of the other side <--- Ring flip done
_ _ _ _ _ _ _ _
When a cyclohexane ring flips conformation, what happens to the equatorial and axial
_ _ _ _ _ _ _ _ _ _ _ _ _
Hydrogens? -- Correct Answer ✔✔ They trade conformations. Axials become
_ _ _ _ _ _ _ _ _ _
equatorials, and equatorials become axials. _ _ _ _
CORRECT ANSWERS
What are the four rules for writing resonance structures? -- Correct Answer ✔✔ 1.
_ _ _ _ _ _ _ _ _ _ _ _ _ _
Atoms must not be moved. Only electrons.
_ _ _ _ _ _
2. All resonance atoms must lie in the same plane.
_ _ _ _ _ _ _ _ _
3. Only valid Lewis structures are allowed.
_ _ _ _ _ _
4 . The number of unpaired electrons must remain constant.
_ _ _ _ _ _ _ _ _
What are the two conditions for resonance? -- Correct Answer ✔✔ 1. An atom must
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
have a P orbital or a lone pair of electrons.
_ _ _ _ _ _ _ _ _
2. It must be single bonded to an atom that has a double or triple bond.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
The latter compromise conjugated unsaturated systems.
_ _ _ _ _
Huckel's Rule -- Correct Answer ✔✔ Planar monocyclic rings with (4n+2) Pi-electrons
_ _ _ _ _ _ _ _ _ _ _ _
must be aromatic (have resonance).
_ _ _ _
What is the condition for a chiral center? -- Correct Answer ✔✔ First, the participant
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
in question cannot be a halogen, a CH2 group, an Oxygen, a Halogen, or any Carbon
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
participating in a double or triple bond. _ _ _ _ _ _
Then list the groups attached to a Carbon. They MUST be four different groups. If the
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
conditions are met, then the Carbon in question is a chiral center.
_ _ _ _ _ _ _ _ _ _ _
,How do you determine Absolution Configuration? -- Correct Answer ✔✔ First,
_ _ _ _ _ _ _ _ _ _ _
prioritize the atoms in terms of atomic weights (if two atoms are the same element,
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
then their substituents are compared to determine priority. Substituents on double and
_ _ _ _ _ _ _ _ _ _ _
_triple bonds count 2 and 3 times, respectively). Now, rotate the sigma bond of the
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Carbon so that the lowest priority group faces away. Next, order the numbers in
_ _ _ _ _ _ _ _ _ _ _ _ _ _
terms of increasing priority. If it increases clockwise, then the atom has "S" absolute
_ _ _ _ _ _ _ _ _ _ _ _ _ _
configuration. if it increases counterclockwise, it has "R" absolute configuration. _ _ _ _ _ _ _ _ _
Does absolute configuration determine rotation of plane polarized light? -- Correct
_ _ _ _ _ _ _ _ _ _ _
Answer ✔✔ No _ _
A chiral molecule's mirror image has the _______ absolute configuration -- Correct
_ _ _ _ _ _ _ _ _ _ _ _
Answer ✔✔ Same _ _
What are the conditions of relative configuration? -- Correct Answer ✔✔ The two
_ _ _ _ _ _ _ _ _ _ _ _ _
atoms in question must differ in the attachment of only one substituent, and the
_ _ _ _ _ _ _ _ _ _ _ _ _ _
remaining substituents must be oriented identically relative to the Carbon.
_ _ _ _ _ _ _ _ _
Observed Rotation -- Correct Answer ✔✔ The degree to which compounds rotate
_ _ _ _ _ _ _ _ _ _ _ _
plane polarized light. _ _
How does a polarimeter work? -- Correct Answer ✔✔ A polarimeter screens out all
_ _ _ _ _ _ _ _ _ _ _ _ _ _
but one group of photons that share the same electromagnetic field orientation.
_ _ _ _ _ _ _ _ _ _ _
What is a racemic mixture? -- Correct Answer ✔✔ A mixture of equal stereoisomers
_ _ _ _ _ _ _ _ _ _ _ _ _ _
that yields optically inactive compounds (optically inactive compounds also arise from
_ _ _ _ _ _ _ _ _ _ _
chirality).
If a compound is labeled "+" or "D", what does that mean? -- Correct Answer ✔✔ It
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
rotates plane polarized light to the right. (Dexter = right in Latin)
_ _ _ _ _ _ _ _ _ _ _
If a compound is labeled "-" or "L", what does that mean? -- Correct Answer ✔✔ It
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
rotates plane polarized light to the left. (Laevus = left in Latin)
_ _ _ _ _ _ _ _ _ _ _
,What are the conditions of stereoisomers? -- Correct Answer ✔✔ Molecules with the
_ _ _ _ _ _ _ _ _ _ _ _ _
same molecular formula and bond to bond connectivity, but are not the same
_ _ _ _ _ _ _ _ _ _ _ _ _
compound.
Stereoisomers must be what (exclude geometric isomers from this definition)? -- _ _ _ _ _ _ _ _ _ _ _
Correct Answer ✔✔ They must have a minimum of 1 chiral center in the same
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
relative three dimensional location. _ _ _
Enantiomers are? -- Correct Answer ✔✔ Enantiomers have the same molecular
_ _ _ _ _ _ _ _ _ _ _
formula, the same bond to bond connectivity, are mirror images of one another, but
_ _ _ _ _ _ _ _ _ _ _ _ _ _
are different molecules.
_ _
Optical Purity is? -- Correct Answer ✔✔ The ratio of observed rotation to pure
_ _ _ _ _ _ _ _ _ _ _ _ _ _
sample rotation. _
What is enantiomeric purity? -- Correct Answer ✔✔ The ratio of pure enantiomer to
_ _ _ _ _ _ _ _ _ _ _ _ _ _
racemic mixture. _
Diastereomers -- Correct Answer ✔✔ Same molecular formula, same bond to bond _ _ _ _ _ _ _ _ _ _ _ _
connectivity, not mirror images, not equal molecules. _ _ _ _ _ _
Why do geometric isomers arise? -- Correct Answer ✔✔ Due to a mitigated ability to
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
rotate about a bond, either via ring closure or multiple bonding.
_ _ _ _ _ _ _ _ _ _
List physical property differences between Cis and Trans isomers? -- Correct Answer
_ _ _ _ _ _ _ _ _ _ _ _
✔✔ Cis isomers have a net dipole moment and thus experience a higher boiling point
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
than Trans isomers. However, because a Cis isomer has lower possible permutations
_ _ _ _ _ _ _ _ _ _ _ _
to form a crystal lattice relative to a Trans isomer, Cis isomers do not form crystals as
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_readily.
Higher order alkanes can be differentiated via substituent by the E-Z method.
_ _ _ _ _ _ _ _ _ _ _ _
Elaborate. -- Correct Answer ✔✔ One were to prioritize the substituents on a
_ _ _ _ _ _ _ _ _ _ _ _ _
Carbon. Then, if one were to note that the higher priority substituent exists on
_ _ _ _ _ _ _ _ _ _ _ _ _ _
opposite sides, it gets the E label (Entgegen: German for Opposite). If the higher
_ _ _ _ _ _ _ _ _ _ _ _ _ _
priority substituents are on the same side, it gets the Z label (Zusamen: German for
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Together)
, What is a meso compound? -- Correct Answer ✔✔ Chiral centers that offset one
_ _ _ _ _ _ _ _ _ _ _ _ _ _
another due to symmetry. The net result is an optically inactive compound. In essence,
_ _ _ _ _ _ _ _ _ _ _ _ _ _
meso compounds are actually a chiral. They can be identified by finding a plane of
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
symmetry that divides the compound into two mirror images.
_ _ _ _ _ _ _ _
What is the formula for maximum number of optically active isomers in a single
_ _ _ _ _ _ _ _ _ _ _ _ _ _
compound? -- Correct Answer ✔✔ 2^n, where n is the number of chiral centers.
_ _ _ _ _ _ _ _ _ _ _ _ _
How many functional groups are methyl, primary, secondary, and tertiary alkyl groups
_ _ _ _ _ _ _ _ _ _ _ _
connected to, respectively? -- Correct Answer ✔✔ 0, 1, 2, and 3, respectively.
_ _ _ _ _ _ _ _ _ _ _ _
List some physical properties of alkanes. -- Correct Answer ✔✔ They have low
_ _ _ _ _ _ _ _ _ _ _ _ _
densities. The more molecular weight an alkane has (more Carbon chains), the higher
_ _ _ _ _ _ _ _ _ _ _ _ _
its boiling point due to intermolecular London Dispersion forces. Branching decreases
_ _ _ _ _ _ _ _ _ _ _
the boiling points because the surface area of the molecule is lowered, and the
_ _ _ _ _ _ _ _ _ _ _ _ _ _
molecule cannot form a more relatively polar transient dipole. Unbranches alkanes also
_ _ _ _ _ _ _ _ _ _ _
_exhibit an increase in melting point in molecular weight, but not as predictable as the
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
boiling point of alkanes. _ _ _
What is ring strain? -- Correct Answer ✔✔ The strain caused by a cycloalkane
_ _ _ _ _ _ _ _ _ _ _ _ _ _
deviating from the optimal SP3 109.5 degree angle. Ring strain is usually alleviated by
_ _ _ _ _ _ _ _ _ _ _ _ _ _
the movement of certain bonds away from a flat three dimensional plane.
_ _ _ _ _ _ _ _ _ _ _
List the relative stabilities of cyclohexane conformers when undergoing a ring flip. --
_ _ _ _ _ _ _ _ _ _ _ _ _
Correct Answer ✔✔ Chair (low) _ _ _ _
Half Chair (highest)
_ _
Twist (lower than Half Chair)
_ _ _ _
Boat (higher than twist but lower than Half Chair)
_ _ _ _ _ _ _ _
Twist of the other side _ _ _ _
Half chair of the other side
_ _ _ _ _
Chair of the other side <--- Ring flip done
_ _ _ _ _ _ _ _
When a cyclohexane ring flips conformation, what happens to the equatorial and axial
_ _ _ _ _ _ _ _ _ _ _ _ _
Hydrogens? -- Correct Answer ✔✔ They trade conformations. Axials become
_ _ _ _ _ _ _ _ _ _
equatorials, and equatorials become axials. _ _ _ _
