Chapter 18 - Chapter 18 Carboxylic Acids Chem 212 B. R....

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Chem 212 B. R. Kaafarani 1 Chapter 18 Carboxylic Acids
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Chem 212 B. R. Kaafarani 2 Systematic IUPAC names replace "-e" ending of alkane with "oic acid“. Table 19.1 (page 792) Systematic Name O HCOH O HOCCH 2 COH methanoic acid propanedioic acid benzenecarboxylic acid Common Name formic acid malonic acid benzoic acid 18.1. Carboxylic Acid Nomenclature Check out common of acetic acid, stearic acid, lactic acid, mandelic acid, acrylic acid, oleic acid, salicylic acid, succinic acid, phthalic acid and know their systematic names. Examples: O C OH O
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Chem 212 B. R. Kaafarani 3 Functional Groups – Hierarchy and Classification Subordinate groups are azides (azido), halides (halo), and nitro (nitro). These groups have no established priority order. Priority high low
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Chem 212 B. R. Kaafarani 4 Formic acid is planar C O H H O 120 pm 134 pm 18.2. Structure and Bonding
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Chem 212 B. R. Kaafarani 5 Stabilizes carbonyl group Electron Delocalization R C O H O •• R C O H O •• + •• R C O H O •• + ••
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Chem 212 B. R. Kaafarani 6 Boiling Points Intermolecular forces, especially hydrogen bonding, are stronger in carboxylic acids than in other compounds of similar shape and molecular weight. bp (1 atm) 31°C 80°C 99°C OH 141°C OH O O 18.3. Physical Properties
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Chem 212 B. R. Kaafarani 7 Hydrogen-bonded Dimers H 3 CC O H O CCH 3 O H O Acetic acid exists as a hydrogen-bonded dimer in the gas phase. The hydroxyl group of each molecule is hydrogen-bonded to the carbonyl oxygen of the other.
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Chem 212 B. R. Kaafarani 8 Solubility in Water H 3 CC O H O O H O H H H Carboxylic acids are similar to alcohols in respect to their solubility in water. Carboxylic acids of 4 carbons or fewer are soluble in water. Form hydrogen bonds to water.
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Chem 212 B. R. Kaafarani 9 CH 3 CO H O CH 3 CH 2 O H p K a = 4.7 p K a = 16 18.4. Acidity of Carboxylic Acids Most carboxylic acids have a pK a close to 5. Carboxylic acids are weak acids. But carboxylic acids are far more acidic than alcohols.
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Chem 212 B. R. Kaafarani 10 Free Energies of Ionization A difference of G °= 64 kJ/mol (free energy of ionization) for ethanol vs. acetic acid.
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Chem 212 B. R. Kaafarani 11 Greater acidity of carboxylic acids is attributed to the stabilization of carboxylate ion by Inductive effect of carbonyl group: RC O O + Resonance stabilization of carboxylate ion: •• RC O O •• •• •• •• RC O O
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Chem 212 B. R. Kaafarani 12 Figure 18.3: Electrostatic potential maps of ethoxide and acetate ion Ethoxide Acetate
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Chem 212 B. R. Kaafarani 13 X CH 2 COH O X H F Cl p K a 4.7 2.6 2.9 Electronegative groups increase acidity X H CH 3 CH 3 (CH 2 ) 5 p K a 4.7 4.9 4.9 Alkyl groups have negligible effect 18.5. Substituent Effects on Acidity Standard of comparison is acetic acid (X = H)
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Chem 212 B. R. Kaafarani 14 Electronegative substituents withdraw electrons from carboxyl group; increase K for loss of H + .
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Chapter 18 - Chapter 18 Carboxylic Acids Chem 212 B. R....

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