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ALDEHYDES AND KETONES
 

ALDEHYDES AND KETONES

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TEMA PARA LA MATERIA DE QUÍMICA...t/t

TEMA PARA LA MATERIA DE QUÍMICA...t/t

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    ALDEHYDES AND KETONES ALDEHYDES AND KETONES Presentation Transcript

    • Organic Chemistry 4th EditionQBA Miguel A. Castro Ramírez Chapter 18 Carbonyl Compounds II Radicals Irene Lee Case Western Reserve University Cleveland, OH
    • Nomenclature of Aldehydes
    • If the aldehyde group is attached to a ring,
    • If a compound has two functional groups, the one with thelowest priority is indicated by its prefix
    • Nomenclature of Ketones
    • If a ketone has a second functional group of higherpriority,
    • An aldehyde has a greater partial positive charge on itscarbonyl carbon than does a ketone
    • • 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
    • Aldehydes and ketones react with nucleophiles to formaddition products: nucleophile addition reactions
    • If the nucleophile that adds to the aldehyde or ketone isan O or an N, a nucleophilic addition–elimination reactionwill occur
    • Formation of a New Carbon–Carbon Bond Using Grignard ReagentsGrignard reagents react with aldehydes, ketones, andcarboxylic acid derivatives
    • Reaction with Acetylide Ions
    • Reduction by Hydride Ion
    • Utilization of DIBAL to Control the Reduction Reaction
    • The reduction of a carboxylic acid with LiAlH4 forms asingle primary alcoholAcyl chloride is also reduced by LiAlH4 to yield an alcohol
    • An amide is reduced by LiAlH4 to an amine
    • Aldehydes and ketones react with a primary amine toform an imineThis is a nucleophilic addition–elimination reactionThe pH of the reaction must be controlled
    • Dependence of the rate of the reaction of acetone withhydroxylamine on the pH of the reaction: a pH rate profile
    • Aldehydes and ketones react with secondary amines toform enamines
    • Formation of Imine Derivatives
    • Deoxygenation of the Carbonyl Group
    • Water adds to an aldehyde or ketone to form a hydrate
    • Why is there such a difference in the Keq values?
    • The equilibrium constant for the reaction depends on therelative stabilities of the reactants and products
    • Addition of an Alcohol to an Aldehyde or a Ketone
    • Utilization of Protecting Groups in SynthesisLiAlH4 will reduce the ester to yield an alcohol, butthe keto group will also be reduced
    • The keto group is protected as a ketal in this synthesis
    • The more reactive aldehyde is protected with the diolbefore reaction with the Grignard reagent
    • • 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
    • Addition of Sulfur Nucleophiles
    • Desulfurization replaces the C–S bonds with C–H bonds
    • Formation of Alkenes The Wittig Reaction
    • Preparation of the Phosphonium YlideIf two sets of reagents are available for the synthesis ofan alkene, it is better to use the one that requires the lesssterically hindered alkyl halides
    • • 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 (C=O) that can share the carbanion’s negative charge
    • Stereochemistry of Nucleophilic Addition Reaction
    • • Nucleophiles that form unstable addition products formconjugated addition products, because the conjugateaddition 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 sterichindrance, a Grignard reagent will form the conjugateaddition product
    • Nucleophilic Addition to α,β-Unsaturated Carboxylic Acid Derivatives
    • Enzyme-Catalyzed Additions to α,β-Unsaturated Carbonyl Compounds