المحاضرة 8: الأحماض الكربوكسيلية ومشتقاتها

Study Notes

Lecture 8: Carboxylic Acids and Derivatives

Topic: Carboxylic acids and their derivatives, a lecture covering nomenclature, acidic character, factors affecting acidity, and various derivatives.
Intended Learning Outcomes (ILOs): Students will be able to demonstrate the chemistry of carboxylic acids containing aromatic compounds, understand the effect of substituents on acidity, and describe various synthesis and properties in terms of acidity.
Introduction: Carboxylic acids are derivatives of hydrocarbons containing one or more carboxyl groups (-COOH) in their molecules.
General Formula: R-COOH, where R represents an alkyl or aryl group. Carboxyl groups can be written as -CO₂H or -COOH.
Specific Examples: Examples of carboxylic acids including 4-Methyl hexanoic acid and 4-Hexenoic acid (or hex-4-enoic acid) were shown.
Common names and IUPAC names: Phthalic acid (IUPAC: 1,2-benzene dicarboxylic acid), Isophthalic acid (IUPAC: 1,3-benzene dicarboxylic acid), Terephthalic acid (IUPAC: 1,4-benzene dicarboxylic acid), Anthranilic acid (2-aminobenzoic acid) are examples of aromatic carboxylic acid derivatives.
Preparation of Carboxylic Acids: Various methods for preparing carboxylic acids were discussed, including oxidation of alkenes, aldehydes and alcohols, alkylbenzenes, and hydrolysis of nitriles and cyanohydrins. Specific chemical reactions and conditions (KMnO4, OH-, H3O+, heat) were mentioned.
Acidity of Carboxylic Acids: Carboxylic acids are typically weak acids, partially dissociating into H+ and RCOO- in neutral aqueous solutions. Aromatic carboxylic acids are more acidic than phenols and alcohols.
Factors Affecting Acidity: Factors like substituent effects (electron-donating (EDG) groups and electron-withdrawing (EWG) groups. Electronegativity, inductive effects, and resonance play a vital role. Examples were presented using reactions where base strength and solubility were also explicitly mentioned.
pKa values: pKa values (the negative log of the acid dissociation constant) are important for classifying the strength of acids. Data was presented for comparison of pKa values for different carboxylic acids. A relationship between pKa, electronegativity, and functional groups was shown.
Hybridization Effect on Acidity: Sp hybridized carbocations have a greater tendency to form strong acids because the s orbitals are closer to the nucleus than p orbitals.
Resonance/Delocalization Effect on Acidity: Resonance delocalization is a stabilizing factor within the conjugate base anion. Delocalization of charge stabilizes the conjugate base, making the carboxylic acid stronger.
Substitution on Benzoic acid: Electron-withdrawing groups (EWGs) stabilize the conjugate base and increase acidity. Electron-donating groups (EDGs) destabilize the conjugate base and decrease acidity.
Nomenclature of Derivatives: Rules for naming acyl chlorides, esters, amides, and anhydrides. Specific examples: propanoyl chloride, ethanoyl chloride, benzoyl chloride, ethyl ethanoate, methyl propanoate, N-methylpropanamide, benzamide etc. were used for illustration.
Nucleophilic Substitution Reactions: Reactions of carboxylic acid derivatives with nucleophiles. Conversion of one derivative to another were presented (e.g. acid chloride to amide to ester). The relative reactivity of carboxylic acid derivatives in nucleophilic substitution was detailed.
Preparation of Acyl Chlorides: Methods for preparing acyl chlorides from carboxylic acids (using SOCl₂ or PCl₃/PCl₅).