CHEM 219 | CHEM219 Module 7: Principles of
Organic Chemistry with Lab - Portage Learning
Updated and Latest Questions and Correct
Answers with Rationale
1. Which of the following factors primarily accounts for the high acidity of carboxylic acids
compared to alcohols?
A. The presence of a single oxygen atom in the structure.
B. Resonance stabilization of the resulting carboxylate anion.
C. The high electronegativity of the carbon atom in the alkyl group.
D. The ability of alcohols to form stronger internal hydrogen bonds.
Correct Answer: B
Expert Explanation: Carboxylic acids are more acidic because the conjugate base is
stabilized by resonance. The negative charge is delocalized over two electronegative
oxygen atoms in the carboxylate ion. In contrast, alcohols form alkoxide ions where the
charge is localized on one oxygen. This delocalization significantly lowers the potential
energy of the anion. Consequently, the equilibrium shifts to favor the release of a proton.
2. Arrange the following carboxylic acid derivatives in order of decreasing reactivity toward
nucleophilic acyl substitution.
A. Ester > Amide > Acid chloride > Acid anhydride
B. Amide > Ester > Acid anhydride > Acid chloride
C. Acid chloride > Ester > Acid anhydride > Amide
D. Acid chloride > Acid anhydride > Ester > Amide
Correct Answer: D
Expert Explanation: Reactivity is determined by the electronic effects and the leaving
group’s ability to depart. Acid chlorides are most reactive because chloride is a very weak
base and an excellent leaving group. Acid anhydrides follow as the carboxylate leaving
group is also relatively stable. Esters are less reactive than anhydrides due to the resonance
donation from the alkoxy group. Amides are the least reactive because the amino group is a
poor leaving group and provides strong resonance stabilization.
3. In a laboratory setting, which reagent is commonly used to convert a carboxylic acid into an
acid chloride?
A. Thionyl chloride (SOCl2)
B. Sodium hydroxide (NaOH)
,C. Hydrochloric acid (HCl)
D. Sodium chloride (NaCl)
Correct Answer: A
Expert Explanation: Thionyl chloride is the standard reagent for synthesizing acid
chlorides from carboxylic acids. The reaction is efficient because the side products, SO2 and
HCl, are both gases. These gases escape the reaction mixture, driving the reaction to
completion according to Le Chatelier’s principle. This method avoids the need for complex
purification of the final product. Other reagents like PCl3 or PCl5 can also be used for this
transformation.
4. What is the characteristic functional group transformation that occurs during Fischer
esterification?
A. Carboxylic acid and alcohol to an ester
B. Aldehyde to carboxylic acid
C. Ester to a carboxylic acid and alcohol
D. Amide to a carboxylic acid
Correct Answer: A
Expert Explanation: Fischer esterification involves the reaction of a carboxylic acid with
an alcohol in the presence of an acid catalyst. The process is a nucleophilic acyl substitution
where the hydroxyl group of the acid is replaced by an alkoxy group. This reaction is
reversible and reaches an equilibrium state. To maximize the yield of ester, one can use an
excess of alcohol or remove water as it forms. The mechanism proceeds through a
tetrahedral intermediate following protonation of the carbonyl oxygen.
5. During the hydrolysis of an amide under acidic conditions, what are the final products?
A. A carboxylate salt and an alcohol
B. An ester and an amine
C. A carboxylic acid and an ammonium salt
D. An aldehyde and ammonia
Correct Answer: C
Expert Explanation: Acid-catalyzed hydrolysis of an amide requires heating and strong
acid. The nitrogen is protonated, making it a better leaving group in the form of an amine.
Water acts as the nucleophile to attack the carbonyl carbon. In the presence of excess acid,
the resulting amine is immediately converted into an ammonium salt. This irreversible
protonation of the amine drives the overall reaction forward.
, 6. Which intermediate is formed during the nucleophilic acyl substitution reaction of an ester
with a nucleophile?
A. Tetrahedral intermediate
B. Carbocation intermediate
C. Free radical intermediate
D. Pentacoordinate transition state
Correct Answer: A
Expert Explanation: Nucleophilic acyl substitution begins with the nucleophilic attack on
the electrophilic carbonyl carbon. This addition step breaks the pi bond and creates a
tetrahedral intermediate. In this intermediate, the carbon atom transitions from sp2 to sp3
hybridization. The intermediate then collapses when the carbonyl pi bond reforms and the
leaving group is expelled. This two-step process (addition followed by elimination) is the
hallmark of derivative chemistry.
7. How does the addition of an electron-withdrawing group (like -Cl) to the alpha-carbon of a
carboxylic acid affect its pKa?
A. It decreases the pKa, making it a stronger acid.
B. It increases the pKa, making it a weaker acid.
C. It has no effect on the pKa.
D. It makes the acid completely insoluble in water.
Correct Answer: A
Expert Explanation: Electron-withdrawing groups increase the acidity of carboxylic acids
through the inductive effect. These groups pull electron density away from the carboxylate
group. This stabilization of the negative charge on the conjugate base makes the proton
easier to remove. A more stable conjugate base corresponds to a lower pKa value.
Therefore, chloroacetic acid is significantly more acidic than acetic acid.
8. In the synthesis of Aspirin (acetylsalicylic acid), what is the role of salicylic acid?
A. It acts as the nucleophile.
B. It acts as the catalyst.
C. It acts as the solvent.
D. It acts as the leaving group.
Correct Answer: A
Expert Explanation: Salicylic acid contains a phenolic hydroxyl group that participates in
the reaction. This hydroxyl group acts as a nucleophile when it attacks the carbonyl of
Organic Chemistry with Lab - Portage Learning
Updated and Latest Questions and Correct
Answers with Rationale
1. Which of the following factors primarily accounts for the high acidity of carboxylic acids
compared to alcohols?
A. The presence of a single oxygen atom in the structure.
B. Resonance stabilization of the resulting carboxylate anion.
C. The high electronegativity of the carbon atom in the alkyl group.
D. The ability of alcohols to form stronger internal hydrogen bonds.
Correct Answer: B
Expert Explanation: Carboxylic acids are more acidic because the conjugate base is
stabilized by resonance. The negative charge is delocalized over two electronegative
oxygen atoms in the carboxylate ion. In contrast, alcohols form alkoxide ions where the
charge is localized on one oxygen. This delocalization significantly lowers the potential
energy of the anion. Consequently, the equilibrium shifts to favor the release of a proton.
2. Arrange the following carboxylic acid derivatives in order of decreasing reactivity toward
nucleophilic acyl substitution.
A. Ester > Amide > Acid chloride > Acid anhydride
B. Amide > Ester > Acid anhydride > Acid chloride
C. Acid chloride > Ester > Acid anhydride > Amide
D. Acid chloride > Acid anhydride > Ester > Amide
Correct Answer: D
Expert Explanation: Reactivity is determined by the electronic effects and the leaving
group’s ability to depart. Acid chlorides are most reactive because chloride is a very weak
base and an excellent leaving group. Acid anhydrides follow as the carboxylate leaving
group is also relatively stable. Esters are less reactive than anhydrides due to the resonance
donation from the alkoxy group. Amides are the least reactive because the amino group is a
poor leaving group and provides strong resonance stabilization.
3. In a laboratory setting, which reagent is commonly used to convert a carboxylic acid into an
acid chloride?
A. Thionyl chloride (SOCl2)
B. Sodium hydroxide (NaOH)
,C. Hydrochloric acid (HCl)
D. Sodium chloride (NaCl)
Correct Answer: A
Expert Explanation: Thionyl chloride is the standard reagent for synthesizing acid
chlorides from carboxylic acids. The reaction is efficient because the side products, SO2 and
HCl, are both gases. These gases escape the reaction mixture, driving the reaction to
completion according to Le Chatelier’s principle. This method avoids the need for complex
purification of the final product. Other reagents like PCl3 or PCl5 can also be used for this
transformation.
4. What is the characteristic functional group transformation that occurs during Fischer
esterification?
A. Carboxylic acid and alcohol to an ester
B. Aldehyde to carboxylic acid
C. Ester to a carboxylic acid and alcohol
D. Amide to a carboxylic acid
Correct Answer: A
Expert Explanation: Fischer esterification involves the reaction of a carboxylic acid with
an alcohol in the presence of an acid catalyst. The process is a nucleophilic acyl substitution
where the hydroxyl group of the acid is replaced by an alkoxy group. This reaction is
reversible and reaches an equilibrium state. To maximize the yield of ester, one can use an
excess of alcohol or remove water as it forms. The mechanism proceeds through a
tetrahedral intermediate following protonation of the carbonyl oxygen.
5. During the hydrolysis of an amide under acidic conditions, what are the final products?
A. A carboxylate salt and an alcohol
B. An ester and an amine
C. A carboxylic acid and an ammonium salt
D. An aldehyde and ammonia
Correct Answer: C
Expert Explanation: Acid-catalyzed hydrolysis of an amide requires heating and strong
acid. The nitrogen is protonated, making it a better leaving group in the form of an amine.
Water acts as the nucleophile to attack the carbonyl carbon. In the presence of excess acid,
the resulting amine is immediately converted into an ammonium salt. This irreversible
protonation of the amine drives the overall reaction forward.
, 6. Which intermediate is formed during the nucleophilic acyl substitution reaction of an ester
with a nucleophile?
A. Tetrahedral intermediate
B. Carbocation intermediate
C. Free radical intermediate
D. Pentacoordinate transition state
Correct Answer: A
Expert Explanation: Nucleophilic acyl substitution begins with the nucleophilic attack on
the electrophilic carbonyl carbon. This addition step breaks the pi bond and creates a
tetrahedral intermediate. In this intermediate, the carbon atom transitions from sp2 to sp3
hybridization. The intermediate then collapses when the carbonyl pi bond reforms and the
leaving group is expelled. This two-step process (addition followed by elimination) is the
hallmark of derivative chemistry.
7. How does the addition of an electron-withdrawing group (like -Cl) to the alpha-carbon of a
carboxylic acid affect its pKa?
A. It decreases the pKa, making it a stronger acid.
B. It increases the pKa, making it a weaker acid.
C. It has no effect on the pKa.
D. It makes the acid completely insoluble in water.
Correct Answer: A
Expert Explanation: Electron-withdrawing groups increase the acidity of carboxylic acids
through the inductive effect. These groups pull electron density away from the carboxylate
group. This stabilization of the negative charge on the conjugate base makes the proton
easier to remove. A more stable conjugate base corresponds to a lower pKa value.
Therefore, chloroacetic acid is significantly more acidic than acetic acid.
8. In the synthesis of Aspirin (acetylsalicylic acid), what is the role of salicylic acid?
A. It acts as the nucleophile.
B. It acts as the catalyst.
C. It acts as the solvent.
D. It acts as the leaving group.
Correct Answer: A
Expert Explanation: Salicylic acid contains a phenolic hydroxyl group that participates in
the reaction. This hydroxyl group acts as a nucleophile when it attacks the carbonyl of
