ChemistryChapter 11: Carbonyl Compounds
11.3 Reactivity
The main idea is that the carboxyl group shows the chemistry of both the carbonyl (C=O) and the hydroxyl (-OH) groups
Explanation level
In the previous sections, we learned about the acidity of carboxylic acids and the preparation of benzoic acid. Now, we will explore the reactivity of carboxylic acids. The carboxyl group (-COOH) is a complex functional group that exhibits the chemistry of both a carbonyl group (C=O) and a hydroxyl group (-OH). Understanding its reactivity is key to understanding the many reactions of carboxylic acids and their derivatives.
Main Idea
The main idea is that the carboxyl group shows the chemistry of both the carbonyl (C=O) and the hydroxyl (-OH) groups. In most reactions, the carboxyl group is retained. However, the reactivity of these molecules is due to the presence of the carbonyl group. The carbonyl carbon is electron-deficient (electrophilic) and is susceptible to attack by nucleophiles. The -OH group can act as a leaving group (after protonation) or can be involved in acid-base reactions.
Core Concept
- Reactions involving the H atom of the -OH group (acidic properties).
- Reactions involving the -OH group (replacement of -OH by other groups, forming derivatives).
- Reactions involving the carboxyl group as a whole (e.g., reduction, decarboxylation).
Detailed Explanation
The textbook states that the carboxyl group shows the chemistry of both the carbonyl (C=O) and the hydroxyl (-OH) groups. In most reactions, the carboxyl group is retained. However, the reactivity of these molecules is due to the presence of the carbonyl group.
1. Reactions Involving the H Atom of the Carboxyl Group (Acidic Properties)
Carboxylic acids are weaker acids than mineral acids. They produce H^+ ions when dissolved in water: R-COOH + H2O ⇌ R-COO- + H3O+ This reaction involves the H atom of the -OH group. The acidity of carboxylic acids was discussed in detail in section 11.1. The acidic proton can be removed by bases to form salts (e.g., sodium carboxylate). This is a key reaction that distinguishes carboxylic acids from other carbonyl compounds.
2. Reactions Involving the OH Group (Formation of Carboxylic Acid Derivatives)
The addition of a nucleophile to the carboxyl group is always followed by the displacement of the -OH group by some other group, producing a carboxylic acid derivative. The -OH group can be replaced by X, OR, and NH_2 to form halides, esters, and amides respectively.
- Reaction with Thionyl Chloride (SOCl2): Acyl chlorides are prepared by treating the carboxylic acid with thionyl chloride in the presence of a base (pyridine). The -OH group is replaced by -Cl. R-COOH + SOCl2 → R-COCl + SO2 + HCl - Reaction with Phosphorus Halides: Phosphorus(III) chloride (PCl3) and phosphorus(V) chloride (PCl5) also convert carboxylic acids to acyl chlorides. 3R-COOH + PCl3 → 3R-COCl + H3PO3 R-COOH + PCl5 → R-COCl + POCl3 + HCl - Formation of Esters: Carboxylic acids react with alcohols in the presence of an acid catalyst to form esters (Fischer esterification). The -OH group is replaced by -OR. R-COOH + R'-OH ⇌ R-COOR' + H2O - Formation of Amides: Carboxylic acids react with ammonia or amines to form amides. The -OH group is replaced by -NH₂ or -NHR. R-COOH + NH3 → R-CONH2 + H2O
3. Reactions Involving the Carboxyl Group as a Whole
These reactions involve changes to the entire carboxyl group, such as reduction or decarboxylation.
- Reduction: Carboxylic acids can be reduced to primary alcohols using strong reducing agents like lithium aluminum hydride (LiAlH4). R-COOH LiAlH4→ R-CH2OH - Decarboxylation: Carboxylic acids can lose carbon dioxide (decarboxylation) when heated with soda lime (NaOH + CaO). R-COONa + NaOH CaO, Δ→ R-H + Na2CO3
Summary of the Three Types of Reactions
| Type of Reaction | Involves | Example |
|---|---|---|
| Acidic Properties | H atom of -OH | R-COOH + NaOH → R-COONa + H2O |
| Formation of Derivatives | -OH group | R-COOH + SOCl2 → R-COCl + SO2 + HCl |
| Reactions of the Carboxyl Group | Entire -COOH group | R-COOH LiAlH4→ R-CH2OH |
Intermediate Level
The reactivity of carboxylic acids is centered on the carboxyl group, which combines the properties of a carbonyl group and a hydroxyl group. The carbonyl carbon is electrophilic and can be attacked by nucleophiles. The -OH group can act as a leaving group after protonation, leading to substitution reactions that form carboxylic acid derivatives such as acyl chlorides, esters, and amides. These reactions are fundamental in organic synthesis. Additionally, the acidic proton of the -OH group can be removed by bases to form salts. The entire carboxyl group can also be modified, for example, by reduction to a primary alcohol or by decarboxylation. The three types of reactions (acidic, substitution, and whole-group reactions) cover the main reactivity of carboxylic acids.
Important Points
- - Carboxyl group: Shows the chemistry of both carbonyl and hydroxyl groups.
- - Reactivity: Due to the electrophilic carbonyl carbon.
- - Three types of reactions:
- 1. Acidic: Loss of H⁺ from -OH.
- 2. Substitution: Replacement of -OH to form derivatives (acyl chlorides, esters, amides).
- 3. Whole-group reactions: Reduction, decarboxylation.
- - Reagents for substitution: SOCl2, PCl3, PCl5, alcohols, ammonia.
- - Reduction: LiAlH4 reduces -COOH to -CH2OH.
- - Decarboxylation: Loss of CO2 from carboxylate salts.
Remember
- - Carboxyl group = carbonyl + hydroxyl.
- - Carbonyl carbon is electrophilic.
- - Acidic reaction: H of -OH is lost.
- - Substitution: -OH is replaced (e.g., -Cl, -OR, -NH₂).
- - Acyl chloride: R-COOH + SOCl2 → R-COCl + SO2 + HCl.
- - Ester: R-COOH + R'-OH ⇌ R-COOR' + H2O.
- - Amide: R-COOH + NH3 → R-CONH2 + H2O.
- - Reduction: R-COOH LiAlH4→ R-CH2OH.
Common Mistakes
- - Thinking that the -OH group is a good leaving group by itself. It is a poor leaving group and must be protonated (or converted to a better leaving group) before substitution can occur.
- - Forgetting that the reaction involves the carbonyl carbon. Nucleophiles attack the carbonyl carbon, not the -OH oxygen.
- - Confusing the three types of reactions. Acidic reactions involve the H of -OH; substitution reactions involve replacing the -OH; whole-group reactions modify the entire carboxyl group.
- - Assuming that carboxylic acids undergo addition reactions like ketones. They undergo substitution (nucleophilic acyl substitution) rather than simple addition.
- - Not recognizing the role of the tetrahedral intermediate. This is a key intermediate in the substitution mechanism.
Quick Revision
- Acidic reactions: The H atom of the -OH group is lost to form salts.
- Substitution reactions: The -OH group is replaced by other groups (e.g., -Cl, -OR, -NH₂) to form carboxylic acid derivatives such as acyl chlorides, esters, and amides.
- Whole-group reactions: The entire carboxyl group is modified, for example, by reduction to a primary alcohol or by decarboxylation.
The formation of derivatives is a key aspect of carboxylic acid chemistry and is widely used in organic synthesis.
60-Second Revision
Carboxylic acids are reactive because of the carboxyl group (-COOH), which behaves like both a carbonyl and a hydroxyl group. The carbonyl carbon is electrophilic, allowing nucleophiles to attack. The three main types of reactions are: acidic reactions (loss of H⁺), substitution reactions (replacement of -OH to form derivatives like acyl chlorides, esters, and amides), and whole-group reactions (reduction to alcohols, decarboxylation). Common reagents include SOCl2 for acyl chlorides and LiAlH4 for reduction.
Frequently Asked Questions (FAQs)
Q1. Why is the carboxyl group considered to have the chemistry of both a carbonyl and a hydroxyl group? Answer: The carboxyl group (-COOH) consists of a carbonyl group (C=O) and a hydroxyl group (-OH) attached to the same carbon atom. The carbonyl part is responsible for the electrophilic reactivity (nucleophilic attack at the carbonyl carbon). The hydroxyl part is responsible for the acidic properties (loss of the proton) and can act as a leaving group in substitution reactions. Therefore, the carboxyl group exhibits the chemistry of both functional groups.
- Acidic reactions: Involving the H atom of the -OH group (e.g., reaction with NaOH to form a salt).
- Substitution reactions: Involving the replacement of the -OH group by another group (e.g., formation of acyl chlorides, esters, and amides).
- Whole-group reactions: Involving the entire carboxyl group (e.g., reduction to a primary alcohol, decarboxylation).
Q3. How are acyl chlorides prepared from carboxylic acids? Answer: Acyl chlorides can be prepared by treating carboxylic acids with thionyl chloride (SOCl2), phosphorus(III) chloride (PCl3), or phosphorus(V) chloride (PCl5). For example: R-COOH + SOCl2 → R-COCl + SO2 + HCl The -OH group of the carboxylic acid is replaced by a -Cl atom.
Q4. What is Fischer esterification? Answer: Fischer esterification is the reaction of a carboxylic acid with an alcohol in the presence of an acid catalyst (e.g., concentrated H2SO4) to form an ester and water: R-COOH + R'-OH ⇌ R-COOR' + H2O This is a reversible reaction and is used to synthesize esters.
- Q5. How are amides formed from carboxylic acids?
- Answer: Amides are formed by the reaction of carboxylic acids with ammonia or amines. For example:
- R-COOH + NH3 → R-CONH2 + H2O
- The -OH group is replaced by the -NH₂ group.
- Q6. What is the product of the reduction of a carboxylic acid?
- Answer: Carboxylic acids are reduced to primary alcohols using a strong reducing agent like lithium aluminum hydride (LiAlH4):
- R-COOH LiAlH4→ R-CH2OH
Q7. What is decarboxylation? Answer: Decarboxylation is the loss of carbon dioxide (CO2) from a carboxyl group. It is typically carried out by heating a carboxylic acid salt (e.g., sodium carboxylate) with soda lime (NaOH + CaO): R-COONa + NaOH CaO, Δ→ R-H + Na2CO3
Q8. Why is the -OH group a poor leaving group in nucleophilic acyl substitution? Answer: The -OH group is a poor leaving group because the hydroxide ion (OH-) is a strong base. In nucleophilic acyl substitution, the -OH group must be protonated (or converted into a better leaving group, such as -Cl in acyl chlorides) before it can be displaced by a nucleophile. This is why carboxylic acids are less reactive than acyl chlorides.
Q9. What is the role of the tetrahedral intermediate in the reactions of carboxylic acids? Answer: In nucleophilic acyl substitution, the nucleophile attacks the carbonyl carbon to form a tetrahedral intermediate. This intermediate then collapses, expelling the leaving group (e.g., -OH after proton transfer) and forming the new C-Nu bond. The tetrahedral intermediate is a key step in the mechanism of these reactions.
Multiple Choice Questions (MCQs)
- Q1. Which part of the carboxyl group is responsible for its acidic properties?
- A. The carbonyl oxygen
- B. The H atom of the -OH group
- C. The carbon atom
- D. The -OH oxygen
- Correct Answer: B
- Explanation: The acidic properties of carboxylic acids are due to the H atom of the -OH group, which can be lost as a proton.
- Q2. Which of the following is a carboxylic acid derivative?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. All of the above
- Correct Answer: D
- Explanation: Acyl chlorides, esters, and amides are all derivatives of carboxylic acids.
- Q3. What is the product of the reaction between a carboxylic acid and thionyl chloride (SOCl2)?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
- Q4. What is the product of the reaction between a carboxylic acid and an alcohol?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: B
- Explanation: The product is an ester.
- Q5. What is the product of the reaction between a carboxylic acid and ammonia?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: C
- Explanation: The product is an amide.
- Q6. What is the reducing agent used to convert a carboxylic acid to a primary alcohol?
- A. LiAlH4
- B. NaBH4
- C. H2/Pd
- D. KMnO4
- Correct Answer: A
- Explanation: Lithium aluminum hydride (LiAlH4) is a strong reducing agent that reduces carboxylic acids to primary alcohols.
- Q7. What is the reaction called when a carboxylic acid salt loses carbon dioxide upon heating?
- A. Esterification
- B. Decarboxylation
- C. Reduction
- D. Oxidation
- Correct Answer: B
- Explanation: Decarboxylation is the loss of carbon dioxide.
- Q8. Which of the following is NOT a reaction of carboxylic acids?
- A. Acidic reaction with NaOH
- B. Substitution with SOCl2
- C. Addition of Br2 across the C=O bond
- D. Reduction with LiAlH4
- Correct Answer: C
- Explanation: Carboxylic acids do not undergo addition reactions across the C=O bond like ketones. They undergo nucleophilic acyl substitution.
- Q9. What is the role of the carbonyl carbon in the reactions of carboxylic acids?
- A. It acts as a nucleophile.
- B. It acts as an electrophile.
- C. It acts as a base.
- D. It acts as a catalyst.
- Correct Answer: B
- Explanation: The carbonyl carbon is electrophilic and is attacked by nucleophiles.
- Q10. What is the product of the reaction of a carboxylic acid with PCl5?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
Multiple Choice Questions (MCQs)
- Q1. Which part of the carboxyl group is responsible for its acidic properties?
- A. The carbonyl oxygen
- B. The H atom of the -OH group
- C. The carbon atom
- D. The -OH oxygen
- Correct Answer: B
- Explanation: The acidic properties are due to the H atom of the -OH group.
- Q2. Which of the following is a carboxylic acid derivative?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. All of the above
- Correct Answer: D
- Explanation: All are derivatives.
- Q3. What is the product of the reaction between a carboxylic acid and thionyl chloride (SOCl2)?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
- Q4. What is the product of the reaction between a carboxylic acid and an alcohol?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: B
- Explanation: The product is an ester.
- Q5. What is the product of the reaction between a carboxylic acid and ammonia?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: C
- Explanation: The product is an amide.
- Q6. What is the reducing agent used to convert a carboxylic acid to a primary alcohol?
- A. LiAlH4
- B. NaBH4
- C. H2/Pd
- D. KMnO4
- Correct Answer: A
- Explanation: LiAlH4 is used to reduce carboxylic acids to primary alcohols.
- Q7. What is the reaction called when a carboxylic acid salt loses carbon dioxide upon heating?
- A. Esterification
- B. Decarboxylation
- C. Reduction
- D. Oxidation
- Correct Answer: B
- Explanation: Decarboxylation is the loss of CO2.
- Q8. Which of the following is NOT a reaction of carboxylic acids?
- A. Acidic reaction with NaOH
- B. Substitution with SOCl2
- C. Addition of Br2 across the C=O bond
- D. Reduction with LiAlH4
- Correct Answer: C
- Explanation: Carboxylic acids do not undergo addition reactions across the C=O bond.
- Q9. What is the role of the carbonyl carbon in the reactions of carboxylic acids?
- A. It acts as a nucleophile.
- B. It acts as an electrophile.
- C. It acts as a base.
- D. It acts as a catalyst.
- Correct Answer: B
- Explanation: The carbonyl carbon is electrophilic.
- Q10. What is the product of the reaction of a carboxylic acid with PCl5?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
Multiple Choice Questions (MCQs)
- Q1. What is the functional group in a carboxylic acid?
- A. -OH
- B. -COOH
- C. -CHO
- D. -CO-
- Correct Answer: B
- Explanation: The functional group is -COOH.
- Q2. What is the product of the reaction of a carboxylic acid with SOCl2?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
- Q3. What is the product of the reaction of a carboxylic acid with an alcohol?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: B
- Explanation: The product is an ester.
- Q4. What is the product of the reaction of a carboxylic acid with ammonia?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: C
- Explanation: The product is an amide.
- Q5. What is the product of the reduction of a carboxylic acid with LiAlH4?
- A. Primary alcohol
- B. Secondary alcohol
- C. Tertiary alcohol
- D. Aldehyde
- Correct Answer: A
- Explanation: The product is a primary alcohol.
- Q6. What is decarboxylation?
- A. Loss of CO2
- B. Loss of H2O
- C. Loss of H2
- D. Loss of O2
- Correct Answer: A
- Explanation: Decarboxylation is the loss of CO2.
- Q7. Which of the following is a good leaving group in nucleophilic acyl substitution?
- A. OH-
- B. Cl-
- C. NH2-
- D. CH3-
- Correct Answer: B
- Explanation: Cl- is a good leaving group.
- Q8. Which of the following is a poor leaving group?
- A. Cl-
- B. Br-
- C. OH-
- D. I-
- Correct Answer: C
- Explanation: OH- is a poor leaving group.
- Q9. What is the role of the carbonyl carbon in the reactions of carboxylic acids?
- A. It acts as a nucleophile.
- B. It acts as an electrophile.
- C. It acts as a base.
- D. It acts as a catalyst.
- Correct Answer: B
- Explanation: The carbonyl carbon is electrophilic.
- Q10. What is the product of the reaction of a carboxylic acid with PCl5?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
Multiple Choice Questions (MCQs)
- Q1. What is the functional group in a carboxylic acid?
- A. -OH
- B. -COOH
- C. -CHO
- D. -CO-
- Correct Answer: B
- Explanation: The functional group is -COOH.
- Q2. What is the product of the reaction of a carboxylic acid with SOCl2?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
- Q3. What is the product of the reaction of a carboxylic acid with an alcohol?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: B
- Explanation: The product is an ester.
- Q4. What is the product of the reaction of a carboxylic acid with ammonia?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: C
- Explanation: The product is an amide.
- Q5. What is the product of the reduction of a carboxylic acid with LiAlH4?
- A. Primary alcohol
- B. Secondary alcohol
- C. Tertiary alcohol
- D. Aldehyde
- Correct Answer: A
- Explanation: The product is a primary alcohol.
- Q6. What is decarboxylation?
- A. Loss of CO2
- B. Loss of H2O
- C. Loss of H2
- D. Loss of O2
- Correct Answer: A
- Explanation: Decarboxylation is the loss of CO2.
- Q7. Which of the following is a good leaving group in nucleophilic acyl substitution?
- A. OH-
- B. Cl-
- C. NH2-
- D. CH3-
- Correct Answer: B
- Explanation: Cl- is a good leaving group.
- Q8. Which of the following is a poor leaving group?
- A. Cl-
- B. Br-
- C. OH-
- D. I-
- Correct Answer: C
- Explanation: OH- is a poor leaving group.
- Q9. What is the role of the carbonyl carbon in the reactions of carboxylic acids?
- A. It acts as a nucleophile.
- B. It acts as an electrophile.
- C. It acts as a base.
- D. It acts as a catalyst.
- Correct Answer: B
- Explanation: The carbonyl carbon is electrophilic.
- Q10. What is the product of the reaction of a carboxylic acid with PCl5?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
Multiple Choice Questions (MCQs)
- Q1. Which of the following is a reaction of carboxylic acids?
- A. Acidic reaction with NaOH
- B. Substitution with SOCl2
- C. Reduction with LiAlH4
- D. All of the above
- Correct Answer: D
- Explanation: All are reactions of carboxylic acids.
- Q2. What is the product of the reaction of a carboxylic acid with SOCl2?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
- Q3. What is the product of the reaction of a carboxylic acid with an alcohol?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: B
- Explanation: The product is an ester.
- Q4. What is the product of the reaction of a carboxylic acid with ammonia?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: C
- Explanation: The product is an amide.
- Q5. What is the product of the reduction of a carboxylic acid with LiAlH4?
- A. Primary alcohol
- B. Secondary alcohol
- C. Tertiary alcohol
- D. Aldehyde
- Correct Answer: A
- Explanation: The product is a primary alcohol.
- Q6. What is decarboxylation?
- A. Loss of CO2
- B. Loss of H2O
- C. Loss of H2
- D. Loss of O2
- Correct Answer: A
- Explanation: Decarboxylation is the loss of CO2.
- Q7. Which of the following is a good leaving group in nucleophilic acyl substitution?
- A. OH-
- B. Cl-
- C. NH2-
- D. CH3-
- Correct Answer: B
- Explanation: Cl- is a good leaving group.
- Q8. Which of the following is a poor leaving group?
- A. Cl-
- B. Br-
- C. OH-
- D. I-
- Correct Answer: C
- Explanation: OH- is a poor leaving group.
- Q9. What is the role of the carbonyl carbon in the reactions of carboxylic acids?
- A. It acts as a nucleophile.
- B. It acts as an electrophile.
- C. It acts as a base.
- D. It acts as a catalyst.
- Correct Answer: B
- Explanation: The carbonyl carbon is electrophilic.
- Q10. What is the product of the reaction of a carboxylic acid with PCl5?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
Multiple Choice Questions (MCQs)
- Q1. Which of the following is a reaction of carboxylic acids?
- A. Acidic reaction with NaOH
- B. Substitution with SOCl2
- C. Reduction with LiAlH4
- D. All of the above
- Correct Answer: D
- Explanation: All are reactions of carboxylic acids.
- Q2. What is the product of the reaction of a carboxylic acid with SOCl2?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
- Q3. What is the product of the reaction of a carboxylic acid with an alcohol?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: B
- Explanation: The product is an ester.
- Q4. What is the product of the reaction of a carboxylic acid with ammonia?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: C
- Explanation: The product is an amide.
- Q5. What is the product of the reduction of a carboxylic acid with LiAlH4?
- A. Primary alcohol
- B. Secondary alcohol
- C. Tertiary alcohol
- D. Aldehyde
- Correct Answer: A
- Explanation: The product is a primary alcohol.
- Q6. What is decarboxylation?
- A. Loss of CO2
- B. Loss of H2O
- C. Loss of H2
- D. Loss of O2
- Correct Answer: A
- Explanation: Decarboxylation is the loss of CO2.
- Q7. Which of the following is a good leaving group in nucleophilic acyl substitution?
- A. OH-
- B. Cl-
- C. NH2-
- D. CH3-
- Correct Answer: B
- Explanation: Cl- is a good leaving group.
- Q8. Which of the following is a poor leaving group?
- A. Cl-
- B. Br-
- C. OH-
- D. I-
- Correct Answer: C
- Explanation: OH- is a poor leaving group.
- Q9. What is the role of the carbonyl carbon in the reactions of carboxylic acids?
- A. It acts as a nucleophile.
- B. It acts as an electrophile.
- C. It acts as a base.
- D. It acts as a catalyst.
- Correct Answer: B
- Explanation: The carbonyl carbon is electrophilic.
- Q10. What is the product of the reaction of a carboxylic acid with PCl5?
- A. Acyl chloride
- B. Ester
- C. Amide
- D. Alcohol
- Correct Answer: A
- Explanation: The product is an acyl chloride.
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Revision Zone
Review the key facts, formulas and checks before you move on.11.3 Reactivity
Sticky Notes · Quick Revision
Key Point 1
- **Carboxyl group:** C=O + -OH.
Key Point 2
- Reactivity: Carbonyl carbon is electrophilic.
Key Point 3
- Three reactions: Acidic, substitution, whole-group.
Key Point 4
- Acidic: H⁺ is lost.
Key Point 5
- Substitution: -OH is replaced.
Key Point 6
- Acyl chloride: SOCl2, PCl3, PCl5.
Key Point 7
- Ester: Alcohol + acid catalyst.
Key Point 8
- Amide: NH3 or amine.
Key Point 9
- Reduction: LiAlH4.
Key Point 10
- Decarboxylation: CO2 loss.
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