Chapter 13 Aldehydes and Ketones Denniston Topping Caret 5 th Edition Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction.

Chapter 13Aldehydes and Ketones

Denniston Topping Caret5th EditionCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Carbonyl CompoundsContain the carbonyl group C=O Aldehydes: R may be hydrogen, usually a carbon containing group

Ketones: R contains carbonShortforms

Structures of Aldehydes and Ketones

13.1 Structure and Physical PropertiesAldehydes and ketones are polar compoundsThe carbonyl group is polar The oxygen end is electronegativeCan hydrogen bond to waterCannot form intermolecular hydrogen bondHydrogenbond

Hydrogen Bonding in Carbonyls13.1 Structure and Physical PropertiesBonding with H2O Intermolecular

Physical PropertiesCarbonyls boil at Higher temperatures than:HydrocarbonsEthers Lower temperatures than:Alcohols 13.1 Structure and Physical Properties

13.2 Nomenclature and Common NamesNaming AldehydesLocate the parent compoundLongest continuous carbon chainMust contain the carbonyl groupReplace the final e of the parent with alNumber the chain with the carbonyl carbon as 1Number and name all substituents

Naming AldehydesWhat is the name of this molecule?Parent chain 5 carbons = pentaneChange suffix pentanalNumber from carbonyl end L to RNumber / name substituents 4-methyl 4-methylpentanal13.2 Nomenclature and Common Names12345

Common Names of AldehydesThese names are taken from Latin roots as are the first 5 carboxylic acidsGreek letters are used to indicate the position of substituents with the carbon atom adjacent or bonded to the carbonyl carbon being the a carbon13.2 Nomenclature and Common Namesg-chlorovaleraldehyde

IUPAC and Common Names With Formulas for Several Aldehydes13.2 Nomenclature and Common Names

Examples of KetonesSimplest ketone MUST have 3 carbon atoms so that the carbonyl group is interiorBase name: longest chain with the C=OReplace the e of alkane name with oneIndicate position of C=O by number on chain so that C=O has lowest possible number

13.2 Nomenclature and Common Names

IUPAC Naming of KetonesRules directly analogous to those for aldehydesBase name: longest chain with the C=O pentReplace the e of alkane name with oneIndicate position of C=O by number on chain so that C=O has lowest possible number 2

4-chloro-2-pentanone13.2 Nomenclature and Common Names12345

Common Names of Ketones

Based on the alkyl groups that are bonded to the carbonyl carbonAlkyl groups are prefixes (2 words) followed by the word ketoneOrder of alkyl groups in the nameAlphabeticalSize smaller to larger Methyl ethyl ketone orEthyl methyl ketone13.2 Nomenclature and Common NamesDimethyl ketone

13.3 Important Aldehydes and KetonesMethanal (b.p. 21oC) is a gas used in aqueous solutions as formalin to preserve tissue Ethanal is produced from ethanol in the liver causing hangover symptomsPropanone (Acetone) is the simplest possible ketoneMiscible with waterFlammableBoth acetone methyl ethyl ketone (MEK or butanone) are very versatile solvents

Important Uses of Carbonyl CompoundsUsed in many industriesFood chemicalsNatural food additivesArtificial additivesFragrance chemicalsMedicinesAgricultural chemicals

Vanillin Vanilla beans2-octanoneMushroom flavor13.3 Important Aldehydes and Ketone

Other Important Carbonyls13.3 Important Aldehydes and Ketone

13.4 Reactions Involving Aldehydes and KetonesPreparation of aldehydes and ketonesPrincipal means of preparation is oxidation of the corresponding alcoholPrimary alcohol produces an aldehydeSecondary alcohol produces a ketoneTertiary alcohol does not oxidizeThis oxidation process removes two hydrogensIt is considered an oxidative elimination reaction

Distinguishing Types of Alcohol Oxidation Upper box shows oxidation of a 1 alcoholMust use a mild oxidizing agent or a carboxylic acid will be formedLower box oxidation of a 2 alcohol to a ketoneTertiary alcohols cannot be oxidized13.4 Reactions Involving Aldehydes and Ketones

Redox Aldehydes: oxidized to carboxylic acidsAldehydes and ketones are reduced to alcohols: aldehydes to primary alcohols and ketones to secondary alcoholsAdditionHydrogen to give alcoholsAlcohols to give hemiacetals, acetals, hemiketals, and ketalsAldehydes/ketones to give aldol (b-hydroxy carbonyl) productsReactions of Aldehydes and Ketones13.4 Reactions Involving Aldehydes and Ketones

Oxidation of AldehydesAldehydes are easily oxidized to carboxylic acids by almost any oxidizing agentSo easily oxidized that it is often difficult to prepare them as they continue on to carboxylic acidsSusceptible to air oxidation even at room temperatureCannot be stored for long periods13.4 Reactions Involving Aldehydes and Ketones

Distinguishing Aldehydes From KetonesVisual tests for the aldehyde functional group based on its easy oxidation are:Tollens TestSilver ion is reduced to silver metalUse a basic solution of Ag(NH3)2+The silver metal precipitates and coats the container producing a smooth silver mirror13.4 Reactions Involving Aldehydes and Ketones

Distinguishing Aldehydes From KetonesBenedicts TestReagent is a buffered aqueous solution of copper(II) hydroxide and sodium citrateReacts with aldehydes, but not generally with ketonesCu2+ is reduced to Cu+Solution of Cu2+ is a distinctive blue color Color fades during the reaction as Cu+ precipitates as the red solid, copper(I) oxide, Cu2O13.4 Reactions Involving Aldehydes and Ketones

Reduction of CarbonylsBoth aldehydes and ketones are readily reduced to alcoholsReduction occurs with hydrogen as the reducing agentClassical reaction is hydrogenationReact with hydrogen gasRequires a catalyst Ni, Pt, PdOccurs with heat and pressure13.4 Reactions Involving Aldehydes and Ketones

Addition ReactionsPrincipal reaction is the addition reaction across the polar C=O double bondVery similar to the addition hydrogenation of alkenesRequires catalytic acid in the solutionProduct of the reaction is a hemiacetalHemiacetals are quite reactiveUndergo a substitution reaction with the OH group of the hemiacetal is exchanged for another OR group from the alcoholReaction product is an acetalThis reaction is reversible13.4 Reactions Involving Aldehydes and Ketones

Formation of Hemiacetal or HemiketalProduct of the addition reaction is a hemiacetal (above) or a hemiketal (below)13.4 Reactions Involving Aldehydes and Ketones

Recognizing Hemiacetals, Acetals, Hemiketals, and Ketals13.4 Reactions Involving Aldehydes and Ketones

Keto-enol TautomersTautomers are isomers which differ in the placement of: A hydrogen atomA double bond The keto form has a C=O while the enol form has a C=C.The keto form is usually the most stable13.4 Reactions Involving Aldehydes and Ketones

Aldol CondensationSelf-addition or condensationUses two molecules of the same aldehyde or ketoneThe a carbon of the second molecule adds to the carbonyl carbon of the first moleculeStrong base such as hydroxide catalyzes the reactionVery complex reaction occurring in multiple steps13.4 Reactions Involving Aldehydes and Ketones

Condensation of an AldehydeAn aldol has an OH b to the carbonyl group13.4 Reactions Involving Aldehydes and Ketones

Aldol Condensation: AldolaseDihydroxyacetone phosphate + D-glyeraldehyde-3-phosphateD-fructose-1,6-bisphosphatea carbon (3) adds to carbonyl carbon (4)13.4 Reactions Involving Aldehydes and Ketones

Reaction SchematicCarbonyl1 Alcohol2 AlcoholHemiketal - KetalHemiacetal - AcetalIf aldehydeIf ketoneIf ketoneIf aldehydeCarboxylic AcidOxidationReductionAddition

Summary of Reactions1. Aldehydes and ketonesa. Oxidation of an aldehydeb. Reduction of aldehydes and ketonesc. Addition reactionsi. Hemiacetal and acetal ii. Hemiketal and ketal2. Keto-enol tautomerization3. Aldol condensation

Summary of Reactions