CHEM 219 Module 7 Problem Set Principles of
Organic Chemistry with Lab FINAL EXAM STUDY
GUIDE 2025/2026 COMPLETE QUESTIONS WITH CORRECT
DETAILED ANSWERS || 100% GUARANTEED PASS
<BRAND NEW VERSION>
1. Define Heterocyle as it applies to organic molecules. - ANSWER ✓ Cyclic
molecules in which one or mroe carbon atoms are replaced by heteratoms -
elements other than carbon or hydrogen.
2. What are two main sub-groups of heterocyclic compounds? - ANSWER ✓
Aliphatic and Aromatic
3. Explain why pyridine is soluble in water. - ANSWER ✓ First - the ability of
pyridine to accept Hydrogen bonding interactions from water molecules due
to the lone pair of electrons in the nitrogen atom. In addition, the
electronegative nitrogen creates a relatively strong dipole moment in the
pyridine molecule, thus making pyridine a polar compound overall.
4. Is pyridine more likely to act as an acid or base? Explain. - ANSWER ✓
Pyridine, like all amines, is a weak base. Amines use the lone pair on the
nitrogen atom to accept protons and thus act as bases.
5. Name the two main classes of reactions that the pyridine molecule will
undergo - - ANSWER ✓ EAS - Electrophilic Aromatic Substitution
NAS - Nucleophilic Aromatic Substitution
6. What is the most important difference between five and six membered
heterocycles in terms of the bonding a the heteroatom? - ANSWER ✓ The
heteroatom of a five-membered ring contributes two electrons (one lone
pair) to the aromatic pi system of the ring to make the molecule aromatic.
This is in sharp contrast to six membered heterocycles where the heteroatom
only contributes one electron to the aromatic pi system.
,7. Explain why Pyrrole is a weaker base than pyridine, even though both are
aromatic, heterocyclic amines. - ANSWER ✓ This is due to the availability
of the lone pair. In pyridine, the lone pair is available (not part of the
aromatic pi system) to accept an acidic proton. In Pyrrole, this is not the
case. Protonation of the lone pair of pyrrole destroys the aromatic pi system
and the special stability of aromaticity; thus, pyrrole is much less likely to
accept an acidic proton on its nitrogen atom.
8. Introduction of a nitrogen to the ring of furan, pyrrole, or Thiophene creates
a family of heterocyclic compounds known as what? - ANSWER ✓ Azoles
9. What is the definition of a fused ring? - ANSWER ✓ In a fused ring system,
two (or more) rings are fused together to form a larger molecule. To be fused
means that each ring shares two (or more) common atoms as a part of the
structure of each ring.
10.The molecule Indole has what ring fused to the C2-C3 bond of a pyrrole
ring? - ANSWER ✓ Benzene
11.Adenine and guanine, two of the nitrogenous bases present in DNA and
RNA , contain what fused ring heterocycle? - ANSWER ✓ Purine
12.Heterocycles - ANSWER ✓ Cyclic organic molecules in which one or more
carbon atoms are replaced by heteroatoms - elements other than C or H.
Largest class of organic compounds known.
13.Most common heteroatoms... - ANSWER ✓ O, N, S
14.Two subgroups of heterocyclic compounds - ANSWER ✓ Aromatic and
Alliphatic (Non-Aromatic)
15.Examples of Non-Aromatic (Aliphatic) Heterocycles - ANSWER ✓
Epoxides, Glucose
16.Pyridine - ANSWER ✓ Six membered heterocyclic analog of benzene.
One of the CH units of the (benzene) ring is replaced by a N atom.
Aromatic
, Tends to undergo substitution reactions rather than addition (which would
destroy aromaticity).
The substitution of the N atom in the ring changes many properties of the
molecule.
17.Pyridine Properties - ANSWER ✓ Miscible in most organic solvents, and
completely miscible with water.
Boiling point is 35 degrees above that of Benzene due to dipole-dipole
attractive forces.
Weak base and will react with strong acids to form pyridinium salts.
The ability if pyridine to act as a base makes it suited to act as a proton
scavenger in acid producing reactions, like the conversion of alcohols to
alkyl chlorides using thionyl chloride.
18.Pyrrole - ANSWER ✓ Much weaker base than pyridine due to the
availability of the lone pair. In pyridine the lone pair is available (not part of
the aromatic pi system) to accept an acidic proton. In Pyrrole, this is not the
case. Protonation of the lone pair of pyrrole destroys the romantic pi system
and special stability of aromaticity; this pyrrole is much less likely to accept
an acidic proton on its nitrogen atom.
19.Bonding of Thiophene and Furan - ANSWER ✓ They have two lone pairs of
their respective heteroatoms. While one pair is involved in the aromatic pi
system, the other is in the same plane as the atoms of the ring and is
available for protonation.
20.Pyridine-Like Atoms - ANSWER ✓ When the nitrogen atom of an aromatic
heterocycle is participating in a pi bond, then the lone pair occupies an sp2
orbital in the same plane as the ring and is available to react as a weak base.
21.Pyrrole-like Atoms - ANSWER ✓ When the nitrogen atom of an aromatic
heterocycle has single binds only then the lone pair participates in the
conjugated pi system to create aromaticity and is not available to react as a
weak base.
22.Substitution at C2 is preferred... - ANSWER ✓ As the carbocation
intermediate that forms during the reaction is delocalized over mroe atoms
(and hence, more stable) when substitution occurs at this position.
, 23.Azoles - ANSWER ✓ N in the place of C3 in Furan, pyrrole or Thiophene.
Oxazole , Imidazole, Thiazole
Inclusion of the N at C3 results in a pyridine-like nitrogen, which is involved
in a pi bond. The lone pair on this N is this available for bonding to acidic
proton.
24.Electrophilic Aromatic Substitution (EAS) - ANSWER ✓ An H is replaced
by an electrophile.
Requires very harsh conditions and occurs very slowly.
Can be nitrated or brominated at very high temperatures and with ver strong
acid catalysis.
Electron withdrawal by the N makes the ring partially positive and this not
as receptive to attack by electrophiles like NO2 or Br.
The strongly acidic conditions cause protonation of the N atom and positive
pyridinium ion is even less attatractive to electrophiles.
When EAS does occur it happens at C3
25.Why is C3 preferred in EAS? - ANSWER ✓ It is preferred as the positive
charge that forms on the carbon during the reaction is the one position that
does not put the positive charge on the electronegative nitrogen via
resonance (especially unstable if the N is already protonated).
26.Nucleophilic Aromatic Substitution (NAS) - ANSWER ✓ Pyridine
undergoes this more easily.
Nucleophile displaces a hydride ion or a halide ion (on a substituted
pyridine) from the aromatic ring. Due to the presence of the N heteroatom
the ring is partially positive and therefore is more attractive to nucleophile
rahter than electrophiles.
Strong nucleophiles like Alkoxide ions (RO-) and amide ions (NH2-) hello
to facilitate the reaction.
27.Azines - ANSWER ✓ Heterocyclic six membered rings with two or more N
atoms present as a part of the ring system.
28.Heterocyclic six-membered rings with two or more N atoms present as a part
of the ring system are known as what type of heterocycles? - ANSWER ✓
Azines
Organic Chemistry with Lab FINAL EXAM STUDY
GUIDE 2025/2026 COMPLETE QUESTIONS WITH CORRECT
DETAILED ANSWERS || 100% GUARANTEED PASS
<BRAND NEW VERSION>
1. Define Heterocyle as it applies to organic molecules. - ANSWER ✓ Cyclic
molecules in which one or mroe carbon atoms are replaced by heteratoms -
elements other than carbon or hydrogen.
2. What are two main sub-groups of heterocyclic compounds? - ANSWER ✓
Aliphatic and Aromatic
3. Explain why pyridine is soluble in water. - ANSWER ✓ First - the ability of
pyridine to accept Hydrogen bonding interactions from water molecules due
to the lone pair of electrons in the nitrogen atom. In addition, the
electronegative nitrogen creates a relatively strong dipole moment in the
pyridine molecule, thus making pyridine a polar compound overall.
4. Is pyridine more likely to act as an acid or base? Explain. - ANSWER ✓
Pyridine, like all amines, is a weak base. Amines use the lone pair on the
nitrogen atom to accept protons and thus act as bases.
5. Name the two main classes of reactions that the pyridine molecule will
undergo - - ANSWER ✓ EAS - Electrophilic Aromatic Substitution
NAS - Nucleophilic Aromatic Substitution
6. What is the most important difference between five and six membered
heterocycles in terms of the bonding a the heteroatom? - ANSWER ✓ The
heteroatom of a five-membered ring contributes two electrons (one lone
pair) to the aromatic pi system of the ring to make the molecule aromatic.
This is in sharp contrast to six membered heterocycles where the heteroatom
only contributes one electron to the aromatic pi system.
,7. Explain why Pyrrole is a weaker base than pyridine, even though both are
aromatic, heterocyclic amines. - ANSWER ✓ This is due to the availability
of the lone pair. In pyridine, the lone pair is available (not part of the
aromatic pi system) to accept an acidic proton. In Pyrrole, this is not the
case. Protonation of the lone pair of pyrrole destroys the aromatic pi system
and the special stability of aromaticity; thus, pyrrole is much less likely to
accept an acidic proton on its nitrogen atom.
8. Introduction of a nitrogen to the ring of furan, pyrrole, or Thiophene creates
a family of heterocyclic compounds known as what? - ANSWER ✓ Azoles
9. What is the definition of a fused ring? - ANSWER ✓ In a fused ring system,
two (or more) rings are fused together to form a larger molecule. To be fused
means that each ring shares two (or more) common atoms as a part of the
structure of each ring.
10.The molecule Indole has what ring fused to the C2-C3 bond of a pyrrole
ring? - ANSWER ✓ Benzene
11.Adenine and guanine, two of the nitrogenous bases present in DNA and
RNA , contain what fused ring heterocycle? - ANSWER ✓ Purine
12.Heterocycles - ANSWER ✓ Cyclic organic molecules in which one or more
carbon atoms are replaced by heteroatoms - elements other than C or H.
Largest class of organic compounds known.
13.Most common heteroatoms... - ANSWER ✓ O, N, S
14.Two subgroups of heterocyclic compounds - ANSWER ✓ Aromatic and
Alliphatic (Non-Aromatic)
15.Examples of Non-Aromatic (Aliphatic) Heterocycles - ANSWER ✓
Epoxides, Glucose
16.Pyridine - ANSWER ✓ Six membered heterocyclic analog of benzene.
One of the CH units of the (benzene) ring is replaced by a N atom.
Aromatic
, Tends to undergo substitution reactions rather than addition (which would
destroy aromaticity).
The substitution of the N atom in the ring changes many properties of the
molecule.
17.Pyridine Properties - ANSWER ✓ Miscible in most organic solvents, and
completely miscible with water.
Boiling point is 35 degrees above that of Benzene due to dipole-dipole
attractive forces.
Weak base and will react with strong acids to form pyridinium salts.
The ability if pyridine to act as a base makes it suited to act as a proton
scavenger in acid producing reactions, like the conversion of alcohols to
alkyl chlorides using thionyl chloride.
18.Pyrrole - ANSWER ✓ Much weaker base than pyridine due to the
availability of the lone pair. In pyridine the lone pair is available (not part of
the aromatic pi system) to accept an acidic proton. In Pyrrole, this is not the
case. Protonation of the lone pair of pyrrole destroys the romantic pi system
and special stability of aromaticity; this pyrrole is much less likely to accept
an acidic proton on its nitrogen atom.
19.Bonding of Thiophene and Furan - ANSWER ✓ They have two lone pairs of
their respective heteroatoms. While one pair is involved in the aromatic pi
system, the other is in the same plane as the atoms of the ring and is
available for protonation.
20.Pyridine-Like Atoms - ANSWER ✓ When the nitrogen atom of an aromatic
heterocycle is participating in a pi bond, then the lone pair occupies an sp2
orbital in the same plane as the ring and is available to react as a weak base.
21.Pyrrole-like Atoms - ANSWER ✓ When the nitrogen atom of an aromatic
heterocycle has single binds only then the lone pair participates in the
conjugated pi system to create aromaticity and is not available to react as a
weak base.
22.Substitution at C2 is preferred... - ANSWER ✓ As the carbocation
intermediate that forms during the reaction is delocalized over mroe atoms
(and hence, more stable) when substitution occurs at this position.
, 23.Azoles - ANSWER ✓ N in the place of C3 in Furan, pyrrole or Thiophene.
Oxazole , Imidazole, Thiazole
Inclusion of the N at C3 results in a pyridine-like nitrogen, which is involved
in a pi bond. The lone pair on this N is this available for bonding to acidic
proton.
24.Electrophilic Aromatic Substitution (EAS) - ANSWER ✓ An H is replaced
by an electrophile.
Requires very harsh conditions and occurs very slowly.
Can be nitrated or brominated at very high temperatures and with ver strong
acid catalysis.
Electron withdrawal by the N makes the ring partially positive and this not
as receptive to attack by electrophiles like NO2 or Br.
The strongly acidic conditions cause protonation of the N atom and positive
pyridinium ion is even less attatractive to electrophiles.
When EAS does occur it happens at C3
25.Why is C3 preferred in EAS? - ANSWER ✓ It is preferred as the positive
charge that forms on the carbon during the reaction is the one position that
does not put the positive charge on the electronegative nitrogen via
resonance (especially unstable if the N is already protonated).
26.Nucleophilic Aromatic Substitution (NAS) - ANSWER ✓ Pyridine
undergoes this more easily.
Nucleophile displaces a hydride ion or a halide ion (on a substituted
pyridine) from the aromatic ring. Due to the presence of the N heteroatom
the ring is partially positive and therefore is more attractive to nucleophile
rahter than electrophiles.
Strong nucleophiles like Alkoxide ions (RO-) and amide ions (NH2-) hello
to facilitate the reaction.
27.Azines - ANSWER ✓ Heterocyclic six membered rings with two or more N
atoms present as a part of the ring system.
28.Heterocyclic six-membered rings with two or more N atoms present as a part
of the ring system are known as what type of heterocycles? - ANSWER ✓
Azines
