1. Ch. 19-20 Lect. 1 Carboxylic Acids and Derivatives
Naming Carboxylic Acids
Common Names used for the simplest acids
Rules for naming carboxylic acids
Assign number 1 to carboxy carbon and number longest chain including it
Replace –ane ending of an alkane with –oic acid ending (or –dioic acid if two)
Number and name any other substituents
Carboxylic acids have priority over any other functional group studied
Cyclic (cycloalkanecarboxylic acids) and aromatic (benzoic acids)

2. Structure and Properties of Carboxylic Acids
Planar sp2 hybridized structure
Hydrogen bonded dimers
High melting and boiling points because of hydrogen bonding (Table 19-2)
NMR of Carboxylic Acids
Proton NMR
Hydroxy proton strongly deshielded and variable ppm
CH2 next to carbonyl is deshielded due to electronegativity: 2-3 ppm
Carbon NMR
Carbonyl carbon similar to aldehydes and ketones, but more shielded 180ppm

4. IR of Carboxylic Acids
Carbonyl stretch at 1700 cm-1
O—H stretch at 2500—3300 is broad due to hydrogen bonding

5. Acid-Base Characteristics of Carboxylic Acids
Fairly strong acids
Electropositive carbonyl carbon pulls electrons away from O—H bond
Resulting carboxylate anion is stabilized by resonance
pKa’s usually between 4 and 5
Electron withdrawing substituents increase the acidity: F3CCOOH pKa = 0.23
Carboxylate anion named as an alkanoate: formate, acetate, pentanoate
Can be bases if protonated by other strong acids
Carbonyl oxygen is the most basic (first one protonated)
Resulting cation is stabilized by resonance (not so if hydroxy is protontated)

6. Synthesis of Carboxylic Acids
Oxidation of primary alcohols and aldehydes by Cr(VI) reagents
KMnO4 and HNO3 can also oxidize alcohols and adehydes to carboxylic acids
2 HNO3 + ClCH2CH2CHO ClCH2CH2COOH NO2 + H2O
Organometallic reagents attack carbon dioxide to give carboxylic acids
CH3CH2Br + Mg CH3CH2MgBr
CH3CH2MgBr + O=C=O CH3CH2COO-
CH3CH2COO H+/H2O CH3CH2COOH
Hydrolysis of a Nitrile is preferred if other functional groups react with Grignard
CH3CH2Br + -C≡N CH3CH2C≡N
CH3CH2C≡N 1. OH- 2. H+/H2O CH3CH2COOH
Mechanism Later!

7. The Addition-Elimination Mechanism
The carboxy carbon is attacked by nucleophiles (like other carbonyls)
In aldehydes and ketones, addition is followed by aqueous workup to give alcohol
In Carboxylic Acids and derivatives, there is a potential leaving group: elimination
Acid Catalyzed Addition-Elimination Mechanism
Base Catalyzed Addition-Elimination Mechanism

8. Notes on Addition-Elimination Reactions
Hydroxide (and other derivitives) are generally poor leaving groups
Acidic Carboxylic Acid will protonate most basic nucleophiles
Formation of Carboxylate anion with strongly basic nucleophilies is irreversible
Weak bases (alcohols, amines, other neutral nucleophiles) can proceed in substitution without deprotonating the acid
Relative Reactivities
Alkanoyl halides > Anhydrides > Esters > Acids > Amides
The potential leaving group decides the reactivity
Electronegative leaving group activates the carbonyl carbon
Resonance stabilizes the carbonyl group