ch 19 20 lect 1 carboxylic acids and derivatives n.
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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

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ch 19 20 lect 1 carboxylic acids and derivatives
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)
slide2
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 10-13 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
slide4
IR of Carboxylic Acids
    • Carbonyl stretch at 1700 cm-1
    • O—H stretch at 2500—3300 is broad due to hydrogen bonding
slide5
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)
slide6
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 + 2 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!

slide7
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
slide8
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