Chapter 4Ketones and Aldehydes

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4.1 Carbonyl StructureCarbon is sp2 hybridized.C=O bond is shorter, stronger, and more polar than C=C bond in alkenes.

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4.2 Carbonyl Compounds=>

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4.3 Naming AldehydesIUPAC: Replace -e with -al.The aldehyde carbon is number 1.If -CHO is attached to a ring, use the suffix -carbaldehyde. There are no cycloaldehydes =>

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Examples3-methylpentanal2-cyclopentenealdehyde

=>benzaldehyde - aromatic

=>

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Small unbranched aldehyde common namesUse the common name of the acid.Drop -ic acid and add -aldehyde.1 C: formic acid, formaldehyde2 Cs: acetic acid, acetaldehyde3 Cs: propionic acid, propionaldehyde4 Cs: butyric acid, butyraldehyde. =>

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4.4 IUPAC Names for KetonesReplace -e with -one. Indicate the position of the carbonyl with a number.Number the chain so that carbonyl carbon has the lowest number.For cyclic ketones the carbonyl carbon is assigned the number 1. =>

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Examples3-methyl-2-butanone3-bromocyclohexanone4-hydroxy-3-methyl-2-butanone =>

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Common Names for Simple KetonesNamed as alkyl attachments to -C=O.methyl isopropyl ketone ethyl isopropyl ketone =>

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Historical Common Namesacetoneacetophenonebenzophenone =>

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Name as SubstituentOn a molecule with a higher priority functional group, C=O is oxo- and -CHO is formyl.Aldehyde priority is higher than ketone.3-methyl-4-oxopentanal3-formylbenzoic acid =>

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4.5 Isomerism in aldehydes and ketonesAldehydes and ketones are constitutional isomersAldehydes and ketones can have skeletal and positional isomers if there are enough carbons.Stereoisomers are also possible if there is a ring or C=C in the molecule

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4.6 Selected Common aldehydes and ketonesFormaldehydeAcetoneVanillinBenzaldehydeCinnamaldehydeButanedione

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FormaldehydeGas at room temperature.Formalin is a 40% aqueous solution.

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Industrial ImportanceAcetone and methyl ethyl ketone are important solvents.Formaldehyde used in polymers like Bakelite.Flavorings and additives like vanilla, cinnamon, artificial butter. =>

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Formaldehyde -formalinAcetone solvent and metabolic productVanillin - vanilla flavoringBenzaldehyde - almond flavorCinnamaldehyde - cinnamonButanedione - butter

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4.7 Physical propertiesBoiling points page 121

Solubility water solubility page 123

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Boiling PointsMore polar, so higher boiling point than comparable alkane or ether.Cannot H-bond to each other, so lower boiling point than comparable alcohol.

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SolubilityGood solvent for alcohols.Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from O-H or N-H.Acetone and acetaldehyde are miscible in water. =>

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4.8 Preparation of Aldehydes and KetonesOxidation2 alcohol + Na2Cr2O7 ketone1 alcohol aldehyde

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4.9 Oxidation and reduction of Aldehydes and ketones

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Tollens TestAdd ammonia solution to AgNO3 solution until precipitate dissolves.Aldehyde reaction forms a silver mirror.

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Oxidation of ketonesKetones no reaction

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Reduction Catalytic HydrogenationKetones give secondary alcoholsAldehydes give primary alcohols

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Reduction: aldehyde + hydrogen --> pri. AlcoholForm of addition reaction.

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Reduction: aldehyde + hydrogen Break hydrogen bond

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Reduction: aldehyde + hydrogen Break double bond and use electrons to bond with hydrogen.

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Reduction: aldehyde + hydrogen Brief Method

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4.10 Addition of AlcoholHemiacetal and Acetal Functional Groups

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Hemiacetal and Acetal Functional Groups Hemiacetal: alcohol and ether on same carbonAcetal: Two ethers on same carbon

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MechanismMust be acid-catalyzed.Adding H+ to carbonyl makes it more reactive with weak nucleophile, ROH.Hemiacetal forms first, then acid-catalyzed loss of water, then addition of second molecule of ROH forms acetal.All steps are reversible. =>

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Hemiacetal Synthesis: aldehyde + alcohol Alcohol + aldehyde --> hemiacetalEthanal + methanolAlcohol oxygen becomes an etherCarbon double bond oxygen becomes an alcohol

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Mechanism for Hemiacetal

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Aldehyde and Ketone Reactions

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Synthesis of Acetal Functional Group Acetal: alcohol plus hemiacetal (ether synthesis)Acetal: Two ethers on same carbon

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Aldehyde and Ketone Reactions

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Mechanism Hemiacetal to Acetal

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Cyclic AcetalsAddition of a diol produces a cyclic acetal.Sugars commonly exist as acetals or hemiacetals.

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SKIP 4.11 AND 4.12

THE END

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Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10Chp 4.1 - 4.10