Chemistry Lecture 8: Carboxylic Acids
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Questions and Answers

What is the primary reason for benzoic acid being a stronger acid than acetic acid?

  • The higher molecular weight of benzoic acid.
  • The presence of an additional hydroxyl group.
  • The electron-withdrawing effect of the phenyl group. (correct)
  • The increased number of hydrogen bonds.

    • How is the nomenclature of acid chlorides structured?

  • Use the -ate ending from the parent alkane.
  • Replace the -ic acid ending with -ate chloride.
  • Replace the -ic acid ending with -yl chloride. (correct)
  • Retain the -ic acid ending and add chloride.

    • Which compound represents a saturated analogue of benzoic acid based on its pKa?

  • Propanoyl chloride
  • Ethanoyl chloride
  • Cyclohexanecarboxylic acid (correct)
  • Phenylacetic acid

    • Which amine derivative can replace the -OH group in carboxylic acids?

    <p>Amide</p> Signup and view all the answers

    Which of the following statements about phenylacetic acid is true?

    <p>It demonstrates the inductive effect of a benzene ring.</p> Signup and view all the answers

    What is the general formula for carboxylic acids?

    <p>R-COOH</p> Signup and view all the answers

    Which of the following compounds is correctly named as a common name?

    <p>Cinnamic acid</p> Signup and view all the answers

    How do substituents affect the acidity of carboxylic acids?

    <p>Electronegative substituents increase acidity.</p> Signup and view all the answers

    Which method is NOT commonly used for the preparation of carboxylic acids?

    <p>Dehydration of alcohols</p> Signup and view all the answers

    Which of the following compounds is an example of an aromatic carboxylic acid?

    <p>Phenyl ethanoic acid</p> Signup and view all the answers

    Which of the following corresponds to a structural feature of carboxylic acids?

    <p>They contain one or more -COOH groups.</p> Signup and view all the answers

    What effect does an electron withdrawing group (EWG) have on the carbonyl group?

    <p>It increases the carbonyl carbon's reactivity.</p> Signup and view all the answers

    Mandelic acid has which of the following IUPAC names?

    <p>2-hydroxy-2-phenyl-ethanoic acid</p> Signup and view all the answers

    Which factor does NOT influence the acidity of carboxylic acids?

    <p>The length of the carbon chain</p> Signup and view all the answers

    Which of the following derivatives is the most reactive towards nucleophilic substitution?

    <p>Acid chloride</p> Signup and view all the answers

    How does the presence of a carboxylate ion affect its reactivity towards nucleophiles?

    <p>It completely repels the approach of nucleophiles.</p> Signup and view all the answers

    Which functional group has a weak electron donating effect?

    <p>Thioester</p> Signup and view all the answers

    What role do electron donating groups (EDGs) play in relation to the carbonyl group?

    <p>They decrease the electrophilic nature of the carbonyl carbon.</p> Signup and view all the answers

    How does the relative reactivity of an acid anhydride compare to that of a thioester?

    <p>Acid anhydride is more reactive than thioester.</p> Signup and view all the answers

    Which substituent is associated with the highest reactivity in nucleophilic substitutions?

    <p>-Cl</p> Signup and view all the answers

    What is the effect of an alkoxy (-OR) group on nucleophilic substitution compared to an amine (-NH2) group?

    <p>Alkoxy is weakly electron donating while amine is very strongly donating.</p> Signup and view all the answers

    What describes the nature of carboxylic acids in an aqueous solution?

    <p>They partially dissociate into H+ and RCOO–.</p> Signup and view all the answers

    How does the strength of carboxylic acids compare to alcohols and phenols?

    <p>Carboxylic acids are stronger than phenols.</p> Signup and view all the answers

    What does the acidity constant (Ka) indicate about an acid?

    <p>A larger Ka value corresponds to a high concentration of H3O+.</p> Signup and view all the answers

    What is the relationship between pKa and acid strength?

    <p>Smaller pKa values represent stronger acids.</p> Signup and view all the answers

    What is the effect of electronegativity on the acidity of a compound?

    <p>Higher electronegativity can stabilize the conjugate base and increase acidity.</p> Signup and view all the answers

    How do electron-withdrawing groups (EWG) affect benzoic acid?

    <p>They increase the acidity by stabilizing the conjugate base.</p> Signup and view all the answers

    Which of the following is true about the ionization of acetic acid?

    <p>It has a Ka value of 1.76 × 10−5.</p> Signup and view all the answers

    What effect do inductive effects of chlorine atoms have on the acidity of carboxylic acids?

    <p>They spread the charge and stabilize the conjugate base.</p> Signup and view all the answers

    What effect do electron-withdrawing groups have on the acidity of benzoic acids?

    <p>They deactivate the benzene ring to electrophilic attack.</p> Signup and view all the answers

    Which hybridization state is associated with greater stability of an anion?

    <p>sp</p> Signup and view all the answers

    Which statement about electron-donating groups is true?

    <p>They destabilize the conjugate base by pushing electron density towards the negative charge.</p> Signup and view all the answers

    What is the effect of resonance on the acidity of a conjugate base?

    <p>It stabilizes charge in the conjugate base.</p> Signup and view all the answers

    Which of the following groups would likely make benzoic acid the least acidic?

    <p>—N(CH3)2</p> Signup and view all the answers

    Order the following groups based on their electron-withdrawing ability, from strongest to weakest: NO2, Cl, CHO.

    <p>NO2, CHO, Cl</p> Signup and view all the answers

    Which of the following has the highest pKa value, indicating the weakest acidity?

    <p>—H</p> Signup and view all the answers

    What general trend is observed as the electronegativity of substituents on a benzene ring increases?

    <p>Decreased stability of the conjugate base and decreased acidity.</p> Signup and view all the answers

    What is the IUPAC name for ethyl acetate?

    <p>Ethyl ethanoate</p> Signup and view all the answers

    How is an anhydride named in IUPAC nomenclature?

    <p>By replacing 'acid' with 'anhydride' in the name of the corresponding acid.</p> Signup and view all the answers

    What is the correct IUPAC name for the compound known as acetamide?

    <p>Ethanamide</p> Signup and view all the answers

    Which of the following statements about nucleophilic substitution reactions is true?

    <p>They involve the substitution of a nucleophile for a leaving group.</p> Signup and view all the answers

    What is the IUPAC name for benzamide?

    <p>N-Ethyl-N-methylbenzamide</p> Signup and view all the answers

    Which compound is correctly paired with its common name?

    <p>Ethanoic anhydride - Acetic anhydride</p> Signup and view all the answers

    Which is a common name for N,N-Dimethylformamide?

    <p>N,N-Dimethylmethanamide</p> Signup and view all the answers

    What is the main structural characteristic of an amide?

    <p>It has a carbonyl group adjacent to an -NH group.</p> Signup and view all the answers

    Study Notes

    Lecture 8: Carboxylic Acids and Their Derivatives

    • Carboxylic acids are derivatives of hydrocarbons containing one or more -COOH groups.
    • General formula: R-COOH (carboxyl group, abbreviated as COOH or -COOH)
    • Specific examples: 4-Methyl hexanoic acid, 4-Hexenoic acid (or hex-4-enoic acid)
    • Intended Learning Outcomes (ILOs):
      • Students will be able to demonstrate the basic chemistry of carboxylic acids containing aromatic compounds.
      • Students will be able to understand effects of substituents on acidity.
      • Students will be able to describe various types of synthesis, properties, and acidity of carboxylic acids containing aromatic compounds.

    Introduction

    • Carboxylic acids are derivatives of hydrocarbons that contain one or more -COOH groups in their molecules.
    • The most important functional group is the carboxyl group (COOH).

    Nomenclature

    • Common names are used for some carboxylic acids, but IUPAC (International Union of Pure and Applied Chemistry) nomenclature is also valid.
    • The general rule is to replace the -ic acid ending in the name of the parent acid by -yl chloride.

    Acidic Character

    • Carboxylic acids are weak acids, partially dissociating into H⁺ and RCOO⁻ ions in neutral aqueous solutions.

    Factors Affecting Acidity

    • Aromatic carboxylic acids are more acidic than phenols, and phenols are more acidic than alcohols.

    Carboxylic Acids and Their Derivatives

    • Carboxylic acids have various derivatives including acid chlorides, anhydrides, esters, and amides.

    Class Activity Questions

    • Q1: Why are carboxylic acids activated?
    • Hint: Consider good vs. poor leaving groups.
    • Q2: Which compound is more acidic? (Three examples of carboxylic acids are shown to compare acidity)
    • Q3: Why are aromatic carboxylic acids more acidic than phenols and alcohols?

    Preparation of Carboxylic Acids

    • Methods for preparing carboxylic acids include oxidation of alkenes, oxidation of aldehydes and alcohols, and oxidation of alkylbenzenes.
    • Carboxylic acids can also be prepared by hydrolysis of nitriles and cyanohydrins.

    Acidity of Carboxylic Acids

    • Carboxylic acids are typically weak acids because they only partially dissociate into H⁺ and carboxylate anions in neutral aqueous solution.
    • Acidity is influenced by various factors, including substituents on the aromatic ring, and hybridization.

    pKa Value of Carboxylic Acids

    • pKa is a measure of acidity, where a smaller pKa value indicates a stronger acid. For example, acetic acid (CH3COOH) has a pKa of ≈4.8, while benzoic acid has a pKa ≈4.2.

    Electronegativity and Acidity

    • Electronegativity and the size of atoms affect the acidity of carboxylic acids.
    • Acidity increases across a period with increasing electronegativity of substituents.
    • Acidity increases down a group with increasing atomic size.

    Inductive Effects on Acidity

    • Inductive effects of substituents influence the acidity of carboxylic acids.
    • Electron-withdrawing groups (EWGs) increase acidity, while electron-donating groups (EDGs) decrease acidity.
    • The inductive effect of chlorine atoms stabilizes the conjugate base of carboxylic acids.

    Resonance/Delocalization Effects on Acidity

    • Resonance delocalization stabilizes the conjugate base, contributing to the acidity.

    Substitution on Benzoic Acid

    • Electron-withdrawing groups (EWGs) stabilize the conjugate base, thus increasing the acidity of the benzoic acid.
    • Electron-donating groups (EDGs) decrease the acidity of the benzoic acid.

    Hybridization Effects on Acidity

    • sp-hybridized anions are more stable than sp² or sp³ anions, due to how close the electrons are to the positively charged nucleus, influencing the carboxylic acid's acidity.

    Nomenclature of Carboxylic Acid Derivatives

    • Provide different names for different carboxylic acid derivatives (acid chlorides, esters, amides, and anhydrides).

    Nucleophilic Substitution Reactions

    • Carboxylic acid derivatives exhibit varying reactivity in nucleophilic substitution reactions.
    • Reactivity is influenced by the inductive effect ,resonance, and hybridization of substituent groups.
    • Electron-withdrawing groups enhance reactivity, and electron-donating groups diminish reactivity to nucleophilic substitution.

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    Lecture 8 Carboxylic Acids and Their Derivatives PDF

    Description

    This quiz covers Lecture 8 on Carboxylic Acids and their derivatives. Students will explore the chemistry of carboxylic acids, their structure, nomenclature, and the effects of substituents on acidity. Prepare to demonstrate your understanding of synthesis, properties, and aromatic compounds.

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