Organic Chemistry Fifth Edition

1
Organic Chemistry II (Chem 234)Professor Duncan
J. Wardrop
Spring 2004
University of Illinois at Chicago
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Electrophilic Alkenes
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18.13Addition of Carbanions to???-Unsaturated
Carbonyl CompoundsThe Michael Reaction
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1,4-Addition of Enolates to a,b-Unsaturated Carbon
yl Compounds - The Michael Reaction

• Stabilized carbanions, such as those derived
  from ?-diketones undergo conjugateaddition to
  ?,?-unsaturated ketones.

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The Michael Reaction - An Example
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Michael Addition is a Useful Process!

• The Michael reaction is a useful method
  forforming carbon-carbon bonds.
• It is also useful in that the product of the
  reaction can undergo an intramolecularaldol
  condensation to form a six-membered ring. One
  such application is called the Robinsonannelation
  .

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Robinson Annelation - A Type of Michael Addition
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Robinson Annelation - The Big Picture
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18.14Conjugate Addition of Organocopper
Reagentsto ???-Unsaturated Carbonyl Compounds
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Addition of Organocopper Reagents
to???-Unsaturated Aldehydes and Ketones

• The main use of organocopper reagents is toform
  carbon-carbon bonds by conjugate addition to
  ?,?-unsaturated ketones.

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Addition of Organocopper Reagents
to???-Unsaturated Aldehydes and Ketones
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Chapter 19Carboxylic Acids
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19.1Carboxylic Acid Nomenclature
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Carboxylic Acid Nomenclature - IUPAC
systematic IUPAC names replace "-e" ending of
alkane with "oic acid"
Systematic Name
methanoic acid
ethanoic acid
octadecanoic acid
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Carboxylic Acid Nomenclature - Trivial

• common names are based on natural origin rather
  than structure

Systematic Name
Common Name
methanoic acid
formic acid
ethanoic acid
acetic acid
octadecanoic acid
stearic acid
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Carboxylic Acid Nomenclature
Systematic Name
Common Name
2-hydroxypropanoicacid
lactic acid
(Z)-9-octadecenoicacid
oleic acid
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19.2Structure and Bonding
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Formic Acid - Carbonyl Carbon is sp2 Hydridized
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Carboxylic Acids are Stabilized by Resonance
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19.3Physical Properties
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Carboxylic Acids - High Boiling Points
bp (1 atm)
31C
80C
99C

• Intermolecular forces, especially hydrogen
  bonding, are stronger in carboxylic acids than in
  other compounds of similar shape and molecular
  weight

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Carboxylic Acids Form Hydogen-Bonded Dimers

• Acetic acid exists as a hydrogen-bonded dimer in
  the gas phase. The hydroxyl group of each
  molecule is hydrogen-bonded to the carbonyl
  oxygen of the other.

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Carboxylic Acids Form Hydogen-Bonded Dimers

• Acetic acid exists as a hydrogen-bonded dimer in
  the gas phase. The hydroxyl group of each
  molecule is hydrogen-bonded to the carbonyl
  oxygen of the other.

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Lower Carboxylic Acids are Soluble in Water

• carboxylic acids are similar to alcohols in
  respect to their solubility in water
• form hydrogen bonds to water

Acids are less soluble in H2O as R increase in
size
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19.4Acidity of Carboxylic Acids

• Most carboxylic acids have a pKa close to 5.

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Carboxylic Acids - Weak Brønsted Acids.

• but far more acidic than alcohols

pKa 4.7
pKa 16
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Carboxylic Acids - Free Energy of Ionization
CH3CH2O H
?G 91 kJ/mol
?G 27 kJ/mol
CH3CH2OH
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Greater acidity of carboxylic acids is
attributedstabilization of carboxylate ion by
a. inductive effect of carbonyl group
b. resonance stabilization of carboxylate ion
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Carboxylic Acids - Electrostatic Potential Energy
Maps
Acetic acid
Acetate ion
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19.5Salts of Carboxylic Acids
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Carboxylic Acids are Neutralized by Strong Bases
carboxlate anion
strongeracid
weakeracid

• equilibrium lies far to the right K is ca. 1011
• as long as the molecular weight of the acid is
  not too high, sodium and potassium carboxylate
  salts are soluble in water

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Long-Chain Carboxylate Salts Form Micelles

• unbranched carboxylic acids with 12-18
  carbonsgive carboxylate salts that form micelles
  inwater

sodium stearate(sodium octadecanoate)

Na
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Long-Chain Carboxylate Salts are Bipolar
ONa
polar
nonpolar
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Formation of Micelles
ONa
polar
nonpolar

• sodium stearate has a polar end (the carboxylate
  end) and a nonpolar "tail"
• the polar end is "water-loving" or hydrophilic
• the nonpolar tail is "water-hating" or
  hydrophobic
• in water, many stearate ions cluster together to
  form spherical aggregates carboxylate ions on
  the outside and nonpolar tails on the inside

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Structure of Micelles
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Structure of Micelles

• The interior of the micelle is nonpolar and has
  the capacity to dissolve nonpolar substances.
• Soaps clean because they form micelles, which
  are dispersed in water.
• Grease (not ordinarily soluble in water)
  dissolves in the interior of the micelle and is
  washed away with the dispersed micelle.

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19.6Substituents and Acid Strength
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The Substituents of Carboxylic Acids Effect
Acidity
standard of comparison is acetic acid (X H)
pKa 4.7
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Carboxylic Acids - Substituent Effects on Acidity
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Carboxylic Acids - Substituent Effects on Acidity

• electronegative substituents withdraw electrons
  from carboxyl group increase K for loss of H

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Effect of Electronegative Substituent
Decreasesas Number of Bonds Between it and
Carboxyl Group Increases.
pKa

ClCH2CH2CH2CO2H
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19.7Ionization ofSubstituted Benzoic Acids
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Carboxylic Acids - Hydridization of
Substituents Effects on Acidity

• sp2-hybridized carbon is more electron-withdrawin
  g than sp3, and sp is more electron-withdrawing
  than sp2

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Ionization of Substituted Benzoic Acids

• effect is small unless X is electronegative
  effect is largest for ortho substituent

pKa Substituent ortho meta para H 4.2 4.2 4.2 CH
3 3.9 4.3 4.4 F 3.3 3.9 4.1 Cl 2.9 3.8 4.0 CH3O 4.
1 4.1 4.5 NO2 2.2 3.5 3.4
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19.8Dicarboxylic Acids
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Dicarboxylic Acids
pKa
Oxalic acid
Malonic acid
Heptanedioic acid

• one carboxyl group acts as an electron-withdrawin
  g group toward the other effect decreases with
  increasing separation

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19.9Carbonic Acid
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Carbonic Acid

H2O
CO2
99.7
0.3

• CO2 is major species present in a solution of
  "carbonic acid" in acidic media

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Carbonic Acid
Ka 5.6 x 10-11
Second ionization constant

H
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19.10Sources of Carboxylic Acids
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Synthesis of Carboxylic Acids - Review

• side-chain oxidation of alkylbenzenes (Section
  11.13)
• oxidation of primary alcohols (Section 15.10)
• oxidation of aldehydes (Section 17.15)

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19.11Synthesis of Carboxylic Acidsby
theCarboxylation of Grignard Reagents
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Synthesis of Carboxylic Acids Carboxylation of
Grignard Reagents

• converts an alkyl (or aryl) halide to a
  carboxylic acid having one more carbon atom than
  the starting halide

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Synthesis of Carboxylic Acids Carboxylation of
Grignard Reagents
?
C
O


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Carboxylation of Grignard Reagents - Example 1
(76-86)
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Carboxylation of Aryl Grignard Reagents
(82)
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19.12Synthesis of Carboxylic Acidsby
thePreparation and Hydrolysis of Nitriles
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Synthesis of Carboxylic Acids Preparation and
Hydrolysis of Nitriles

• converts an alkyl halide to a carboxylic acid
  having one more carbon atom than the starting
  halide
• limitation is that the halide must be reactive
  toward substitution by SN2 mechanism

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Preparation and Hydrolysis of Nitriles - Example
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Preparation and Hydrolysis of Nitriles Preparation
of Dicarboxylic Acids
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Preparation and Hydrolysis of Nitriles Preparation
of Carboxylic Acids from Cyanohydrins
1. NaCN
2. H
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Information Suggested Problems
Suggested Problems 19.13-19.23 ------------------
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fice Hour Today, 3.30 P.M., SES
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