Transcript Chapter 21 Carboxylic Acid Derivatives

Organic Chemistry, 7th Edition
L. G. Wade, Jr.
Chapter 21
Part 1: Structure and Properties of
Carboxylic Acid Derivatives
Copyright © 2010 Pearson Education, Inc.
Acid Derivatives
 All the derivatives can be converted to the
carboxylic acid by acidic or basic hydrolysis.
 Esters and amides are commonly found in
nature.
Chapter 21
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Esters from Carboxylic Acids
 Esters can be made from the carboxylic acid
through the Fischer esterification.
 Excess alcohol is used to drive the equilibrium
toward the ester.
Chapter 21
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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
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Cyclic Esters
 Reaction 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
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Amide Structure
 Amides 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
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Protonation of Amides
 Under acidic conditions, the double-bonded
oxygen will get protonated.
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Classes of Amides
3º amide
2º amide
1º amide
 1 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).
Chapter 21
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Nomenclature of Amides
O CH3
CH3CHC N CH2CH3
N-ethyl-N-methyl-2-dimethylpropanamide
(N-ethyl-N-methylisobutyramide)
CH3
 For 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.
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Cyclic Amides
 Cyclic 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.
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Nitriles
 Nitriles contain the cyano group (—CN).
 They can be hydrolyzed to carboxylic acids.
Chapter 21
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Structures of Acetonitrile and
Propyne
 In 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.
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Naming Nitriles
CN
CH3 C
N
acetonitrile
CH3
CH2 CH
CH2
COOH
3-cyanopentanoic acid
CN
cyclopropanecarbonitrile
 For 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.
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Acid Halides
O
O
R C Cl
R C Br
acid chloride
(acyl chloride)
acid bromide
(acyl bromide)
 Also 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.
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Acid Halide Nomenclature
O
CH3CH2
C Cl
propanoyl chloride
Br
CH3CHCH2
O
C Br
3-bromobutanoyl bromide
 Named by replacing -ic acid with -yl halide.
 Acyl chlorides are more common.
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Acid Anhydrides
 Two 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.
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Anhydride Nomenclature
O
CH3
O
C O C CH3
ethanoic anhydride
(acetic anhydride)
O
CF3
O
O
C O C CF3
trifluoroethanoic anhydride
(trifluoroacetic anhydride)
CH3
O
C O C H
ethanoic methanoic anhydride
(acetic formic anhydride)
 The word acid is replaced with anhydride.
 For a mixed anhydride, name both acids.
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Multifunctional Compounds
 The functional group with the highest priority
determines the parent name.
OH
CH3
CH2
CH C
N
2-hydroxybutanenitrile
acid > ester > amide > nitrile > aldehyde > ketone >
alcohol > amine > alkene > alkyne
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Boiling Points of Carboxylic Acid Derivatives
Chapter 21
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Intermolecular Forces of Amides
Chapter 21
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Melting Points
 Amides 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.
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Solubility
 Acid 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 acetate
 Dimethylformamide (DMF)
 Acetonitrile
Chapter 21
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Common Solvents
Chapter 21
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IR Spectroscopy
Chapter 21
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IR Spectrum of Ethyl Octanoate
Chapter 21
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IR Frequencies of Lactones and
Lactams
• Ring strain in lactones and lactams increases
the carbonyl stretching frequency.
Chapter 21
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IR Spectrum of Propionic
Anhydride
Chapter 21
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1
Typical H–NMR Absorptions
Chapter 21
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NMR Spectra of DMF
Chapter 21
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13C–NMR
Spectroscopy
 The 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.
Chapter 21
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