Chapter 17Chapter 17Aldehydes and Ketones:Aldehydes and Ketones:

Nucleophilic AdditionNucleophilic Additionto theto the

Carbonyl GroupCarbonyl Group

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17.117.1NomenclatureNomenclature

IUPAC Nomenclature of Aldehydes H

O O

H

O HCCHCH

OBase the name on the chain that contains the carbonyl group and replace the -e ending of the hydrocarbon with -al.

4,4-dimethylpentanal 5-hexenalor hex-5-enal

IUPAC Nomenclature of Aldehydes H

O O

H

O HCCHCH

O

2-phenylpropanedial(keep the -e endingbefore -dial)

when named as a substituent

formyl group carbaldehyde orcarboxaldehyde

when named as a suffix

C H

O

IUPAC Nomenclature of Aldehydes

CH3CH2CCH2CH2CH3

O

CH3CHCH2CCH3

O

CH3 H3C O

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

Substitutive IUPAC Nomenclature of Ketones

Substitutive IUPAC Nomenclature of Ketones

CH3CH2CCH2CH2CH3

O

CH3CHCH2CCH3

O

CH3 H3C O

3-hexanoneor hexan-3-one

4-methyl-2-pentanoneor 4-methylpentan-2-one

4-methylcyclohexanone

Functional Class IUPAC Nomenclature of Ketones

CH3CH2CCH2CH2CH3

O O

CH2CCH2CH3

CH CH2

O

H2C CHC

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

CH3CH2CCH2CH2CH3

O

ethyl propyl ketone benzyl ethyl ketone

divinyl ketone

O

CH2CCH2CH3

CH CH2

O

H2C CHC

Functional Class IUPAC Nomenclature of Ketones

17.217.2Structure and Bonding:Structure and Bonding:

The Carbonyl GroupThe Carbonyl Group

planar

bond angles: close to 120°

C=O bond distance: 122 pm

Structure of Formaldehyde

1-butene propanal

The Carbonyl Group O

dipole moment = 0.3D dipole moment = 2.5D

very polar double bond

2475 kJ/mol

2442 kJ/mol

Alkyl groups stabilize carbonyl groups the sameway they stabilize carbon-carbon double bonds,carbocations, and free radicals.

heat of combustion

Carbonyl Group of a Ketone is MoreStable than that of an Aldehyde

O

O

H

Heats of combustion ofC4H8 isomeric alkenes

CH3CH2CH=CH2

2717 kJ/molcis-CH3CH=CHCH3

2710 kJ/moltrans-CH3CH=CHCH3

2707 kJ/mol(CH3)2C=CH2

2700 kJ/mol

2475 kJ/mol

2442 kJ/mol

O

O

H

Spread is Greater forAldehydes and

Ketones than for Alkenes

Nucleophiles attack carbon; electrophiles attack oxygen.

Resonance Description ofCarbonyl Group

C

O •• ••

C

O

+

–•••• ••

Carbon and oxygen are sp2 hybridized.

Bonding in Formaldehyde

The half-filled2p orbitals oncarbon andoxygen overlapto form a bond.

Bonding in Formaldehyde

17.317.3Physical PropertiesPhysical Properties

boiling point

–6°C

49°C

97°C

Aldehydes and Ketones have Higher Boiling Pointsthan Alkenes, but Lower Boiling Points than Alcohols

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

O

OH

17.417.4Sources of Aldehydes and KetonesSources of Aldehydes and Ketones

2-heptanone(component of alarm pheromone of bees)

O

Many Aldehydes and Ketones Occur Naturally

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

Many Aldehydes and Ketones Occur Naturally

O

H

citral (from lemon grass oil)

Many Aldehydes and Ketones Occur Naturally O

H

from alkenes

ozonolysis

from alkynes

hydration (via enol)

from arenes

Friedel-Crafts acylation

from alcohols

oxidation

Table 17.1 Synthesis of Aldehydes and Ketones

A number of reactions alreadystudied provide

efficient syntheticroutes to

aldehydes and ketones.

C

O

R OH

aldehydes from carboxylic acids

RCH2OH

1. LiAlH42. H2O

PDC, CH2Cl2

HC

O

R

What About..?

Benzaldehyde from benzoic acid COH

O CH

O

1. LiAlH42. H2O

PDCCH2Cl2CH2OH

(81%) (83%)

Example

C

O

R H

Ketones from aldehydes

R'RC

O

PDC, CH2Cl21. R'MgX2. H3O+

RCHR'

OH

What About..?

C

O

CH3CH2 H

3-heptanone from propanal

H2CrO4

1. CH3(CH2)3MgX2. H3O+

CH3CH2CH(CH2)3 CH3

OH

O

CH3CH2C(CH2)3 CH3

(57%)

Example