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Chapter 17 Carboxylic Acids And Esters. 17.1 Carboxylic Acids 17.2 Physical Properties of Carboxylic Acids 17.3 Acidity of Carboxylic Acids. Carboxyl Group. The carboxyl group: Is a carbonyl group (C=O) attached to a hydroxyl group (OH).
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Chapter 17 Carboxylic Acids And Esters 17.1 Carboxylic Acids 17.2 Physical Properties of Carboxylic Acids 17.3 Acidity of Carboxylic Acids
Carboxyl Group The carboxyl group: • Is a carbonyl group (C=O) attached to a hydroxyl group (OH). • Is found on carbon 1 in carboxylic acids. • Is written in different ways. O CH3—C—OH CH3—COOH CH3—CO2H
Models of Carboxylic Acids • The three-dimensional models show the geometry of atoms in carboxylic acid molecules.
IUPAC Names The IUPAC names of carboxylic acids: • Replace the -e in the alkane name with -oic acid. CH4 methane HCOOH methanoic acid CH3—CH3 ethane CH3—COOH ethanoic acid • Number substituents from the carboxyl carbon 1. CH3 | CH3—CH—CH2—COOH 4 3 2 1 3-methylbutanoic acid
Common Names The common names of simple carboxylic acids: • Use formic acid (1C), acetic acid (2C), propionic acid (3C), and butyric acid (4C). HCOOH formic acid CH3—COOH acetic acid • Locate substituents by assigning , , γ to the carbon atoms adjacent to the carboxyl carbon. CH3 γ| CH3—CH—CH2—COOH -methylbutryic acid
Aromatic Carboxylic Acids Benzoic acid: • Is the aromatic carboxylic acid. • Locates substituents by assigning 1 to the carbon attached to the carboxyl group. • Has common names that assign prefixes ortho, meta, and para for 2 substituents. ortho 1, 2 location meta 1, 3 location para 1, 4 location
Alpha Hydroxy Acids Alpha hydroxy acids (AHAs): • Occur naturally in fruit, milk, and sugarcane. • Are used in skin care products.
Preparation of Carboxylic Acids • Carboxylic acid can be prepared by oxidizing primary alcohols or aldehydes. • The oxidation of ethanol produces ethanoic acid (acetic acid). OH O O | [O] || [O] || CH3—CH2 CH3—C—HCH3—C—OH Ethanol ethanal ethanoic acid Ethyl alcohol acetaldehyde acetic acid
Boiling Points Carboxylic acids: • Have higher boiling points than alcohols, ketones, and aldehydes of similar mass. • Form dimers in which hydrogen bonds form between two carboxyl groups. O H—O || | CH3cC C—CH3 | || O—H O A dimer of acetic acid
Solubility in Water Carboxylic acids: • With 1-4 carbon atoms are very soluble in water. • Form hydrogen bonds with many water molecules.
Acid Dissociation Constants Carboxylic acids: • Are weak acids. CH3—COOH + H2O CH3—COO– + H3O+ • Exist mostly as molecules and a few ions in aqueous solutions. • Have small Ka values.
Salts of Carboxylic Acids Carboxylic acid salts are: • Formed when a carboxylic acid is neutralized by a strong base. CH3—COOH + NaOH CH3—COO– Na+ + H2O acetic acid sodium acetate (carboxylic acid salt) • Used as preservatives and flavor enhancers.