Carbonyl Compounds II

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Chapter 18 Carbonyl Compounds II Radicals
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Nomenclature of Aldehydes
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If the aldehyde group is attached to a ring,
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If a compound has two functional groups, the one
with the lowest priority is indicated by its
prefix
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Nomenclature of Ketones
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If a ketone has a second functional group of
higher priority,
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An aldehyde has a greater partial positive charge
on its carbonyl carbon than does a ketone
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• Steric factors contribute to the reactivity of
  an aldehyde

• The carbonyl carbon of an aldehyde is more
  accessible
• to the nucleophile

• Ketones have greater steric crowding in their
  transition
• states, so they have less stable transition
  states

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Aldehydes and ketones react with nucleophiles to
form addition products nucleophile addition
reactions
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If the nucleophile that adds to the aldehyde or
ketone is an O or an N, a nucleophilic
additionelimination reaction will occur
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Formation of a New CarbonCarbon Bond Using
Grignard Reagents
Grignard reagents react with aldehydes, ketones,
and carboxylic acid derivatives
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Reaction with Acetylide Ions
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In basic solution, a cyanohydrin is converted
back to the carbonyl compound
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Synthesis Using Cyanohydrin
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Reduction by Hydride Ion
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Utilization of DIBAL to Control the Reduction
Reaction
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The reduction of a carboxylic acid with LiAlH4
forms a single primary alcohol
Acyl chloride is also reduced by LiAlH4 to yield
an alcohol
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An amide is reduced by LiAlH4 to an amine
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Aldehydes and ketones react with a primary amine
to form an imine
This is a nucleophilic additionelimination
reaction The pH of the reaction must be
controlled
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Dependence of the rate of the reaction of acetone
with hydroxylamine on the pH of the reaction a
pH rate profile
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Aldehydes and ketones react with secondary amines
to form enamines
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Formation of Imine Derivatives
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Deoxygenation of the Carbonyl Group
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Water adds to an aldehyde or ketone to form a
hydrate
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Why is there such a difference in the Keq values?
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The equilibrium constant for the reaction depends
on the relative stabilities of the reactants and
products
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Addition of an Alcohol to an Aldehyde or a Ketone
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Utilization of Protecting Groups in Synthesis
LiAlH4 will reduce the ester to yield an alcohol,
but the keto group will also be reduced
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The keto group is protected as a ketal in this
synthesis
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The more reactive aldehyde is protected with the
diol before reaction with the Grignard reagent
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• The OH group in an alcohol can be protected as a
  
• trimethylsilyl ether

• The OH group in a carboxylic acid can be
  protected as
• an ester

• An amino group can be protected with an acetyl
  group

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Addition of Sulfur Nucleophiles
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Desulfurization replaces the CS bonds with CH
bonds
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Formation of Alkenes The Wittig Reaction
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Preparation of the Phosphonium Ylide
If two sets of reagents are available for the
synthesis of an alkene, it is better to use the
one that requires the less sterically hindered
alkyl halides
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• The Wittig reaction is completely regioselective

• This reaction is the best way to make a terminal
  alkene

• Stable ylides form primarily E isomers, and
  unstabilized
• ylides form primarily Z isomers

• Stable ylides have a group (CO) that can share
  the
• carbanions negative charge

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Stereochemistry of Nucleophilic Addition Reaction
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• Nucleophiles that form unstable addition
  products form
• conjugated addition products, because the
  conjugate
• addition is not reversible

• Nucleophiles that form stable addition products
  can
• form direct addition products or conjugate
  addition
• products

• If the rate of direct addition is slowed down by
  steric
• hindrance, a Grignard reagent will form the
  conjugate
• addition product

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Nucleophilic Addition to a,b-Unsaturated
Carboxylic Acid Derivatives
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Enzyme-Catalyzed Additions to a,b-Unsaturated
Carbonyl Compounds