ACS Organic Chemistry Exam Questions with
Answers.
Chapter 1 - Structure: Shape and stability
-Haworth Projections
-Common way to show cyclic molecules
-Up line --> Wedged
-Down line --> Dashed
Molecular orbital diagram
1. fill the lowest energy orbital
2. no orbital may hold more than two electrons and they must be of opposite spin
3. When filling degenerate orbitals (orbitals of the same energy) each orbital receives
one electron, then the degenerate orbitals receive a second electron of the opposite
spin
-AFTER hybridization - only one row (put one spin on each line first then fill the others
-BEFORE hybridization - 2 or more rows (fill the lowest line before moving to higher
lines
-Look up atom in periodic table - column # = valence electrons
Molecular geometry
Dipole Moment
-A dipole moment arises when there is a difference in electronegativity between two
atoms in a bond, causing one end of the bond to become partially negative (δ⁻) and the
other partially positive (δ⁺). This creates a polar bond.
-Less symmetry = stronger dipole
Dipole Moment Strength
1. The greater the difference in electronegativity between two bonded atoms, the
stronger the dipole moment.
2. Hydrogen bonding is strong
3. Does not cancel out is strongest, if something cancel out and is left with a net dipole it
is weaker than one that simply has a net moment without cancelling anything out
Resonance
-same molecular formula
-moves around charges and electrons NOT atoms
Biggest resonance contributor
1. All atoms obey the octet rule (especially for second-period elements like C, N, O,
F).
Atoms should not exceed or fall short of 8 electrons (unless it's an exception like P or
S).
2. Minimal formal charges.
The most stable structure has the fewest formal charges.
A neutral molecule is generally more stable than charged forms.
3. If charges exist, they’re on appropriate atoms:
Negative charges should be on more electronegative atoms (like O or N).
Positive charges should be on less electronegative atoms (like C).
, 4. More covalent bonds (double bonds) = more stability, if the octet rule is still
satisfied.
A structure with more double or delocalized bonds tends to be more stable if it doesn’t
cause an octet violation.
5. Charge separation is minimized.
Structures with separated positive and negative charges are generally less stable than
ones where charges are closer together or nonexistent.
6. Avoid like charges on adjacent atoms.
Two positive or two negative charges next to each other is unstable.
7. Delocalization of electrons (especially charges and π electrons).
If a structure spreads out electron density over multiple atoms (especially in conjugated
systems), it gains stability.
Stability
Benzylic > Allylic > 3 prime > 2 prime > 1 prime > something on a double bond
Chapter 2: Structure - Nomenclature and functional groups
...
IUPAC groups
IUPAC for alcohol
-OH group gets the lowest possible number
IUPAC for alkenes
1. If you have a chain ensure the lowest number goes to the double bond
2. if you have a ring ensure that the double bond gets the number 1
What counts when alphabetizing and naming
-Prefixes that DON'T Count: di,tri,tetra, sec, tert, iso
Common Functional groups
High boiling point
Ionic compounds > Hydrogen bonding > Polar > Nonpolar
Larger molecules > Smaller molecules (if similar IMFs)
Straight chains > Branched chains (if similar IMFs)
-SO FOR TWO COMPOUNDS WITH SIMILAR FUNCTIONAL GROUPS: the larger the
surface area,/MORE SPREAD OUT, the HIGHER the boiling point, and the more
polarizable the atoms, the higher the boiling point
A stronger IMF indicates a higher boiling point
Intermolecular forces
1. dispersion forces (in everything, weakest)
2. dipole-dipole interaction (In polar molecules with permanent dipole moments.)
3. Hydrogen bonding (Occurs when H is covalently bonded to N, O, or F)
4. Ion-dipole interaction (Cation-anion : strongest)
Solubility
-Like dissolves in like
-Alkanes usually do not dissolve in water : the smallest chain the more likely soluble in
water
-More carbons mean LESS soluble
-<5 carbons = likely SOLUBLE in water
->5 carbons = likely INSOLUBLE in water
Chapter 3 - Structure: constitutional, stereochemical & conformational isomers
Answers.
Chapter 1 - Structure: Shape and stability
-Haworth Projections
-Common way to show cyclic molecules
-Up line --> Wedged
-Down line --> Dashed
Molecular orbital diagram
1. fill the lowest energy orbital
2. no orbital may hold more than two electrons and they must be of opposite spin
3. When filling degenerate orbitals (orbitals of the same energy) each orbital receives
one electron, then the degenerate orbitals receive a second electron of the opposite
spin
-AFTER hybridization - only one row (put one spin on each line first then fill the others
-BEFORE hybridization - 2 or more rows (fill the lowest line before moving to higher
lines
-Look up atom in periodic table - column # = valence electrons
Molecular geometry
Dipole Moment
-A dipole moment arises when there is a difference in electronegativity between two
atoms in a bond, causing one end of the bond to become partially negative (δ⁻) and the
other partially positive (δ⁺). This creates a polar bond.
-Less symmetry = stronger dipole
Dipole Moment Strength
1. The greater the difference in electronegativity between two bonded atoms, the
stronger the dipole moment.
2. Hydrogen bonding is strong
3. Does not cancel out is strongest, if something cancel out and is left with a net dipole it
is weaker than one that simply has a net moment without cancelling anything out
Resonance
-same molecular formula
-moves around charges and electrons NOT atoms
Biggest resonance contributor
1. All atoms obey the octet rule (especially for second-period elements like C, N, O,
F).
Atoms should not exceed or fall short of 8 electrons (unless it's an exception like P or
S).
2. Minimal formal charges.
The most stable structure has the fewest formal charges.
A neutral molecule is generally more stable than charged forms.
3. If charges exist, they’re on appropriate atoms:
Negative charges should be on more electronegative atoms (like O or N).
Positive charges should be on less electronegative atoms (like C).
, 4. More covalent bonds (double bonds) = more stability, if the octet rule is still
satisfied.
A structure with more double or delocalized bonds tends to be more stable if it doesn’t
cause an octet violation.
5. Charge separation is minimized.
Structures with separated positive and negative charges are generally less stable than
ones where charges are closer together or nonexistent.
6. Avoid like charges on adjacent atoms.
Two positive or two negative charges next to each other is unstable.
7. Delocalization of electrons (especially charges and π electrons).
If a structure spreads out electron density over multiple atoms (especially in conjugated
systems), it gains stability.
Stability
Benzylic > Allylic > 3 prime > 2 prime > 1 prime > something on a double bond
Chapter 2: Structure - Nomenclature and functional groups
...
IUPAC groups
IUPAC for alcohol
-OH group gets the lowest possible number
IUPAC for alkenes
1. If you have a chain ensure the lowest number goes to the double bond
2. if you have a ring ensure that the double bond gets the number 1
What counts when alphabetizing and naming
-Prefixes that DON'T Count: di,tri,tetra, sec, tert, iso
Common Functional groups
High boiling point
Ionic compounds > Hydrogen bonding > Polar > Nonpolar
Larger molecules > Smaller molecules (if similar IMFs)
Straight chains > Branched chains (if similar IMFs)
-SO FOR TWO COMPOUNDS WITH SIMILAR FUNCTIONAL GROUPS: the larger the
surface area,/MORE SPREAD OUT, the HIGHER the boiling point, and the more
polarizable the atoms, the higher the boiling point
A stronger IMF indicates a higher boiling point
Intermolecular forces
1. dispersion forces (in everything, weakest)
2. dipole-dipole interaction (In polar molecules with permanent dipole moments.)
3. Hydrogen bonding (Occurs when H is covalently bonded to N, O, or F)
4. Ion-dipole interaction (Cation-anion : strongest)
Solubility
-Like dissolves in like
-Alkanes usually do not dissolve in water : the smallest chain the more likely soluble in
water
-More carbons mean LESS soluble
-<5 carbons = likely SOLUBLE in water
->5 carbons = likely INSOLUBLE in water
Chapter 3 - Structure: constitutional, stereochemical & conformational isomers
