Ch16_Lecture

Ch16_Lecture - Chapter 16: Carboxylic Acids Nomenclature:...

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Chapter 16: Carboxylic Acids Nomenclature: Functional group suffix = -oic acid If the acid is substituted onto a ring the suffix -carboxylic acid is used. The anion derived by deprotonation of carboxylic acids, RCO2H, is the carboxylate, RCO2- methanoic acid ethanoic acid propanedioic acid butanedioic acid formic acid acetic acid malonic acid succinic acid Acyl Chlorides Functional group suffix = -oyl chloride Anhydrides Functional group suffix = alkanoic anhydride Esters Functional group suffix = alkyl -oate Functional group prefix = alkoxycarbonyl- or carbalkoxy- Cyclic esters are called lactones = -olide example 5-hexanolide Carboxylic Acids Functional group suffix = -oic acid or -carboxylic acid Functional group prefix = carboxy- Amides Functional group suffix = amide Functional group prefix = carbamoyl- Cyclic amides are called lactams = -olidone Nitriles Functional group suffix = -nitrile or -carbonitrile Functional group prefix = cyano-
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Physical Properties: The polar nature of both the O-H and C=O bonds (due to the electonegativity difference of the atoms) results in the formation of strong hydrogen bonds with other carboxylic acid molecules or other H-bonding systems (e.g. water). The implications are: higher melting and boiling points compared to analogous alcohols high solubility in aqueous media hydrogen bonded dimers in gas phase and dimers or aggregates in pure liquid Structure: The CO2H unit is planar and consistent with sp2 hybridization and a resonance interaction of the lone pairs of the hydroxyl oxygen with the p system of the carbonyl C=O. Acidity: Carboxylic acids are the most acidic simple organic compounds (pKa ~ 5). But they are only weak acids compared to acids like HCl or H 2 SO 4 . (Remember the lower the pKa, the stronger the acid) Resonance stabilization of the carboxylate ion allows the negative charge to be delocalized between the two electronegative oxygen atoms (compare with alcohols, pKa ~ 16). Adjacent electron withdrawing substituents increase the acidity by further stabilizing the carboxylate. Carboxylic Acid Structure pKa Ethanoic acid CH3CO2H 4.7 Propanoic acid CH3CH2CO2H 4.9 Fluoroethanoic acid CH2FCO2H 2.6 Chloroethanoic acid CH2ClCO2H 2.9 Dichloroethanoic acid CHCl2CO2H 1.3 Trichloroethanoic acid CCl3CO2H 0.9 Nitroethanoic acid O2NCH2CO2H 1.7 Reactivity: There is low electron density on H atom of the -CO2H group alcohol, i.e. H+ character. The H atom of the RCO2H is acidic (pKa ~ 5). The most important reactions of carboxylic acids convert them into carboxylic acid derivatives such as acyl halides, esters and amides via nucleophilic acyl substitution reactions.
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Preparation of Carboxylic Acids (overview) Oxidation of Alkenes Oxidation of Oxidation of Alkylbenzenes Oxidation of Benzene Oxidation of Methyl Ketones Haloform Reaction Hydrolysis of Nitriles Carbonation of Grignards KMnO 4 , OH - heat OH HO O O + 1. O 3 2. H 2 O 2 , NaOH H O 1. Ag 2 O or Ag(NH 3 ) 2 + OH - 2. H + H 2 O H 2 CrO 4
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This note was uploaded on 04/09/2008 for the course CHEM 313 taught by Professor Narske during the Spring '08 term at Augustana.

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Ch16_Lecture - Chapter 16: Carboxylic Acids Nomenclature:...

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