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lecture 18- Aldehydes and Ketones

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General Organic Chemistry Two credits Second Semester 2009 King Saud bin Abdulaziz University for Health Science Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. Carey Third Edition Instructor: Rabih O. Al-Kaysi, PhD.
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General

Organic ChemistryTwo credits

Second Semester 2009

King Saud bin Abdulaziz University for Health Science

Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. CareyThird Edition

Instructor: Rabih O. Al-Kaysi, PhD.

Chapter 11Chapter 11

Aldehydes and Aldehydes and KetonesKetones

Lecture 18

Nucleophilic AdditionNucleophilic Additionto theto the

Carbonyl GroupCarbonyl Group

NomenclatureNomenclature

IUPAC Nomenclature of AldehydesIUPAC Nomenclature of Aldehydes HH

OO OO

HH

OO HCCHCHHCCHCH

OOBase the name on the Base the name on the chain that contains chain that contains the carbonyl group the carbonyl group and replace the and replace the -e-e ending of the ending of the hydrocarbon by hydrocarbon by -al-al..

4,4-dimethylpent4,4-dimethylpentananalal 5-hex5-hexenenalal

IUPAC Nomenclature of AldehydesIUPAC Nomenclature of Aldehydes HH

OO OO

HH

OO HCCHCHHCCHCH

OO

2-phenylprop2-phenylpropaneanedialdial(keep the (keep the -e -e endingendingbefore before -dial-dial))

when named as when named as a substituenta substituent

formyl groupformyl group carbaldehyde orcarbaldehyde orcarboxaldehydecarboxaldehyde

when named when named as a suffixas a suffix

CC HH

OO

IUPAC Nomenclature of Aldehydes IUPAC Nomenclature of Aldehydes

CHCH33CHCH22CCHCCH22CHCH22CHCH33

OO

CHCH33CHCHCHCH22CCHCCH33

OO

CHCH33 HH33CC OO

Base the name on the chain Base the name on the chain that contains the carbonyl that contains the carbonyl group and replace group and replace -e-e by by -one-one. . Number the chain in the Number the chain in the direction that gives the lowest direction that gives the lowest number to the carbonyl number to the carbonyl carbon.carbon.

Substitutive IUPAC Nomenclature of KetonesSubstitutive IUPAC Nomenclature of Ketones

Substitutive IUPAC Nomenclature of KetonesSubstitutive IUPAC Nomenclature of Ketones

CHCH33CHCH22CCHCCH22CHCH22CHCH33

OO

CHCH33CHCHCHCH22CCHCCH33

OO

CHCH33 HH33CC OO

3-3-hexanhexanoneone

4-methyl4-methyl-2--2-pentanpentanoneone

4-methylcyclohexan4-methylcyclohexanoneone

Functional Class IUPAC Nomenclature of KetonesFunctional Class IUPAC Nomenclature of Ketones

CHCH33CHCH22CCCHCH22CHCH22CHCH33

OO OO

CHCH22CCCHCH22CHCH33

CHCH CHCH22

OO

HH22CC CHCCHC

List the groups List the groups attached to the attached to the carbonyl separately in carbonyl separately in alphabetical order, and alphabetical order, and add the word add the word ketoneketone..

CHCH33CHCH22CCCHCH22CHCH22CHCH33

OO

ethylethyl propylpropyl ketone ketone benzylbenzyl ethylethyl ketone ketone

divinyl ketonedivinyl ketone

OO

CHCH22CCCHCH22CHCH33

CHCH CHCH22

OO

HH22CC CHCCHC

Functional Class IUPAC Nomenclature of KetonesFunctional Class IUPAC Nomenclature of Ketones

Structure and Bonding:Structure and Bonding:The Carbonyl GroupThe Carbonyl Group

planarplanar

bond angles: close to 120°bond angles: close to 120°

C=O bond distance: 122 pmC=O bond distance: 122 pm

Structure of FormaldehydeStructure of Formaldehyde

1-butene1-butene propanalpropanal

The Carbonyl GroupThe Carbonyl Group OO

dipole moment = 0.3Ddipole moment = 0.3D dipole moment = 2.5Ddipole moment = 2.5D

very polar double bondvery polar double bond

nucleophiles attack carbon; nucleophiles attack carbon; electrophiles attack oxygenelectrophiles attack oxygen

Resonance Description ofResonance Description ofCarbonyl GroupCarbonyl Group

CC

OO •••• ••••

CC

OO

++

––•••••••• ••••

Carbon and oxygen are Carbon and oxygen are spsp22 hybridized hybridized

Bonding in FormaldehydeBonding in Formaldehyde

The half-filledThe half-filledpp orbitals on orbitals oncarbon andcarbon andoxygen oxygen overlapoverlapto form a to form a bondbond

Bonding in FormaldehydeBonding in Formaldehyde

Physical PropertiesPhysical Properties

boiling pointboiling point

––6°C6°C

49°C49°C

97°C97°C

Aldehydes and ketones have higher boilingAldehydes and ketones have higher boilingthan alkenes, but lower boiling points than alcohols.than alkenes, but lower boiling points than alcohols.

More polar than More polar than alkenes, but cannot alkenes, but cannot form intermolecular form intermolecular hydrogen bonds to hydrogen bonds to other carbonyl groupsother carbonyl groups

OO

OHOH

Sources of Aldehydes and KetonesSources of Aldehydes and Ketones

2-heptanone2-heptanone(component of alarm pheromone of bees)(component of alarm pheromone of bees)

OO

Many aldehydes and ketones occur naturallyMany aldehydes and ketones occur naturally

transtrans-2-hexenal -2-hexenal (alarm pheromone of myrmicine ant)(alarm pheromone of myrmicine ant)

Many aldehydes and ketones occur naturallyMany aldehydes and ketones occur naturally

OO

HH

citral (from lemon grass oil)citral (from lemon grass oil)

Many aldehydes and ketones occur naturallyMany aldehydes and ketones occur naturally OO

HH

from alkenesfrom alkenes

ozonolysisozonolysis

from alkynesfrom alkynes

hydration (via enol)hydration (via enol)

from arenesfrom arenes

Friedel-Crafts Friedel-Crafts acylationacylation

from alcoholsfrom alcohols

oxidationoxidation

Synthesis of Aldehydes and KetonesSynthesis of Aldehydes and Ketones

A number of A number of reactions alreadyreactions alreadystudied providestudied provide

efficient syntheticefficient syntheticroutes to routes to

aldehydes and aldehydes and ketones.ketones.

CC

OO

RR OHOH

aldehydes from carboxylic acidsaldehydes from carboxylic acids

RCHRCH22OHOH

1. LiAlH1. LiAlH44

2. H2. H22OOPDC, CHPDC, CH22ClCl22

HHCC

OO

RR

What about..?What about..?

benzaldehyde from benzoic benzaldehyde from benzoic acidacid

COHCOH

OO CHCH

OO

1. LiAlH1. LiAlH44

2. H2. H22OOPDCPDCCHCH22ClCl22

CHCH22OHOH

(81%)(81%) (83%)(83%)

ExampleExample

CC

OO

RR HH

ketones from aldehydesketones from aldehydes

R'R'CC

OO

RR

PDC, CHPDC, CH22ClCl221. 1. R'MgXR'MgX

2. H2. H33OO++

RCHRCHR'R'

OHOH

What about..?What about..?

CC

OO

CHCH33CHCH22 HH

3-heptanone from propanal3-heptanone from propanal

HH22CrOCrO44

1. 1. CHCH33(CH(CH22))33MgXMgX

2. H2. H33OO++

CHCH33CHCH22CHCH(CH(CH22))3 3 CHCH33

OHOH

OO

CHCH33CHCH22CC(CH(CH22))3 3 CHCH33

(57%)(57%)

ExampleExample

Reactions of Aldehydes and Reactions of Aldehydes and

Ketones:Ketones:

A Review and a PreviewA Review and a Preview

Already covered in earlier chapters:Already covered in earlier chapters:

reduction of C=O to CHreduction of C=O to CH22

Clemmensen reductionClemmensen reduction

Wolff-Kishner reductionWolff-Kishner reduction

reduction of C=O to CHOHreduction of C=O to CHOH

addition of Grignard and organolithiumaddition of Grignard and organolithium

reagentsreagents

Reactions of Aldehydes and KetonesReactions of Aldehydes and Ketones

Principles of Nucleophilic Principles of Nucleophilic

Addition to Carbonyl Groups:Addition to Carbonyl Groups:

Hydration of Aldehydes and Hydration of Aldehydes and

KetonesKetones

HH22OO

Hydration of Aldehydes and KetonesHydration of Aldehydes and Ketones

CC••••OO ••••

HOHO CC OO HH••••

••••

••••

••••

compared to Hcompared to H

electronic: electronic: alkyl groups stabilize alkyl groups stabilize reactantsreactants

steric: steric: alkyl groups crowdalkyl groups crowdproductproduct

OHOH

OHOH

RR R'R'++ HH22OO CCCCRR R'R'

OO

Substituent Effects on Hydration EquilibriaSubstituent Effects on Hydration Equilibria

C=OC=O hydratehydrate KK %%RelativeRelative

raterate

CHCH22=O=O CHCH22(OH)(OH)22 23002300 >99.9>99.9 22002200

CHCH33CH=OCH=O CHCH33CH(OH)CH(OH)22 1.01.0 5050 1.01.0

(CH(CH33))33CCH=OCCH=O (CH(CH33))33CCH(OH)CCH(OH)22 0.20.2 1717 0.090.09

(CH(CH33))22C=OC=O (CH(CH33))22C(OH)C(OH)22 0.00140.0014 0.140.14 0.00180.0018

Equilibrium Constants and Relative RatesEquilibrium Constants and Relative Ratesof Hydrationof Hydration

when carbonyl group is when carbonyl group is destabilizeddestabilized

alkyl groups alkyl groups stabilizestabilize C=O C=O

electron-withdrawing groups electron-withdrawing groups destabilizedestabilize C=O C=O

When does equilibrium favor hydrate?When does equilibrium favor hydrate?

OHOH

OHOH

RR RR++ HH22OO CCCCRR RR

OO

Substituent Effects on Hydration EquilibriaSubstituent Effects on Hydration Equilibria

RR = CH = CH33: : KK = 0.000025 = 0.000025

RR = CF = CF33: : KK = 22,000 = 22,000

Mechanism of Hydration (base)Mechanism of Hydration (base)

CC••••OO •••••••• OO ••••

HH

••••

––

Step 1:Step 1:Step 1:Step 1:

++

••••

HOHO CC OO••••

••••

••••••••––

Mechanism of Hydration (base)Mechanism of Hydration (base)

Step 2:Step 2:Step 2:Step 2:

••••OOHH

HH

••••

••••HOHO CC OO

••••

••••

••••••••––

++••••

••••OO

HH

••••––••••

HOHO CC OOHH••••

••••

••••

Mechanism of Hydration (acid)Mechanism of Hydration (acid)

CC••••OO ••••

Step 1:Step 1:Step 1:Step 1:

++ ••••

HH

OOHH

HH++

++

CC

••••OOHH++

•••• ••••

HH

OO

HH

Mechanism of Hydration (acid)Mechanism of Hydration (acid)

Step 2:Step 2:Step 2:Step 2:

CC••••OOHH++

++••••

HH

OO

HH

••••CC OOHH

••••

••••

HH

OO

HH

•••• ++

Mechanism of Hydration (acid)Mechanism of Hydration (acid)

Step 3:Step 3:Step 3:Step 3:

++••••

HH

OO

HH

••••CC OOHH

••••

HHOO

HH

••••

•••• •••• OO

HH

••••CC OOHH

••••

••••

++

HH

HHOO

HH ••••

++

Cyanohydrin FormationCyanohydrin Formation

++

Cyanohydrin FormationCyanohydrin Formation

••••••••CC OO HCNHCN HHCC OONN CC••••

••••

••••

Cyanohydrin FormationCyanohydrin Formation

••••••••CC OO

CC––

NN•••• ••••

Cyanohydrin FormationCyanohydrin Formation

––OONN CC CC••••

•••• ••••••••

HH HH

HH

++OO ••••

HH

HH

OO ••••••••OONN CC CC••••

•••••••• HH

2,4-Dichlorobenzaldehyde2,4-Dichlorobenzaldehydecyanohydrin (100%)cyanohydrin (100%)

ExampleExample

ClCl ClCl CHCH

OOClCl

ClCl CHCNCHCN

OHOHNaCN, waterNaCN, water

then Hthen H22SOSO44

ExampleExample

CHCH33CCHCCH33

OONaCN, waterNaCN, water

then Hthen H22SOSO44

CHCH33CCHCCH33

OHOH

CNCN

(77-78%)(77-78%)

Acetone cyanohydrin is used in the Acetone cyanohydrin is used in the synthesis of methacrylonitrilesynthesis of methacrylonitrile


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