Hóa học - Chapter 21 - Part 1: Structure and properties of carboxylic acid derivatives

Chapter 21Copyright © 2010 Pearson Education, Inc.Organic Chemistry, 7th EditionL. G. Wade, Jr.Part 1: Structure and Properties of Carboxylic Acid DerivativesChapter 21*Acid DerivativesAll the derivatives can be converted to the carboxylic acid by acidic or basic hydrolysis.Esters and amides are commonly found in nature.Chapter 21*Esters from Carboxylic AcidsEsters can be made from the carboxylic acid through the Fischer esterification.Excess alcohol is used to drive the equilibrium toward the ester.Chapter 21*Nomenclature of Esters Esters are named as alkyl carboxylates.The first word is derived from the alkyl group of the alcohol, and the second word from the carboxylate group of the carboxylic acid. Chapter 21*Cyclic EstersReaction of —OH and —COOH on same molecule produces a cyclic ester called lactone.To name, add the word lactone to the IUPAC acid name or replace the -ic acid of common name with -olactone.Chapter 21*Amide StructureAmides are the product of the reaction of a carboxylic acid with ammonia or an amine.Not basic because the lone pair on nitrogen is delocalized by resonance.The C—N bond has double-bond character.Chapter 21*Protonation of AmidesUnder acidic conditions, the double-bonded oxygen will get protonated.Chapter 21*Classes of Amides1 amide has one C—N bond (two N—H).2 amide or N-substituted amide has two C—N bonds (one N—H).3 amide or N,N-disubstituted amide has three C—N bonds (no N—H).3º amide2º amide1º amideChapter 21*Nomenclature of AmidesFor 1 amide, drop -ic or -oic acid from the carboxylic acid name, add -amide.Alkyl groups bonded to nitrogen are named with N-alkyl to indicate their attachment to the nitrogen atom. N-ethyl-N-methyl-2-dimethylpropanamide(N-ethyl-N-methylisobutyramide)CH3CHCNOCH2CH3CH3CH3Chapter 21*Cyclic AmidesCyclic amides are called lactams.To name, add the word lactam to the IUPAC acid name or replace the -ic acid of common name with -olactam.Chapter 21*NitrilesNitriles contain the cyano group (—CN).They can be hydrolyzed to carboxylic acids.Chapter 21*Structures of Acetonitrile and PropyneIn both compounds, the atoms at the ends of the triple bonds are sp hybridized, and the bond angles are 180°. In place of the acetylenic hydrogen atom, the nitrile has a lone pair of electrons in the sp orbital of nitrogen.The nonbonding electrons on the nitrogen are not basic.Chapter 21*Naming NitrilesFor IUPAC names, add -nitrile to the alkane name.The Ethyl Octanoate group can also be named as a substituent, the cyano group.Common names come from the carboxylic acid. Replace -ic acid with -onitrile.Chapter 21*Acid HalidesAlso called acyl halides.These are more reactive than carboxylic acids, so they are used to synthesize other acid derivatives such as esters and amides.Used in the Friedel–Crafts acylation to make acylbenzenes.Chapter 21*Acid Halide NomenclatureNamed by replacing -ic acid with -yl halide.Acyl chlorides are more common.Chapter 21*Acid AnhydridesTwo molecules of acid combine with the loss of water to form the anhydride.Anhydrides are more reactive than acids, but less reactive than acid chlorides.A carboxylate ion is the leaving group in nucleophilic acyl substitution reactions.Chapter 21*Anhydride NomenclatureThe word acid is replaced with anhydride.For a mixed anhydride, name both acids.Chapter 21*Multifunctional CompoundsThe functional group with the highest priority determines the parent name.acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene > alkyneChapter 21*Boiling Points of Carboxylic Acid DerivativesChapter 21*Intermolecular Forces of AmidesChapter 21*Melting PointsAmides have very high boiling points and melting points compared to other compounds of similar weight.Melting points increase with increasing number of N—H bonds.Tertiary amides cannot hydrogen bond, but still have high boiling points.Chapter 21*SolubilityAcid chlorides and anhydrides are too reactive to be used with water or alcohol.Esters, 3 amides, and nitriles are good polar aprotic solvents.Solvents commonly used in organic reactions:Ethyl acetateDimethylformamide (DMF)AcetonitrileCommon SolventsChapter 21*Chapter 21*IR SpectroscopyChapter 21*IR Spectrum of Ethyl OctanoateChapter 21*IR Frequencies of Lactones and Lactams Ring strain in lactones and lactams increases  the carbonyl stretching frequency.Chapter 21*IR Spectrum of Propionic AnhydrideChapter 21*Typical 1H–NMR AbsorptionsChapter 21*NMR Spectra of DMFChapter 21*13C–NMR SpectroscopyThe carbonyl carbons of acid derivatives appear at shifts around 170 to 180 ppm, slightly more shielded than the carbonyl carbons of ketones and aldehydes. The a-carbon atoms absorb around 30 to 40 ppm.