chapter 9 ketones and aldehydes. carbonyl compounds

Chapter 9Ketones and Aldehydes

Carbonyl Compounds

Carbonyl Structure• Carbon is sp2 hybridized.• C=O bond is shorter, stronger, and more

polar than C=C bond in alkenes.

Chapter 9 4

IUPAC Names for Ketones

• Replace -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.

Chapter 9 5

Examples

CH3 C

O

CH

CH3

CH3

O

Br

CH3 C

O

CH

CH3

CH2OH

3-methyl-2-butanone3-methylbutan-2-one 3-bromocyclohexanone

4-hydroxy-3-methyl-2-butanone4-hydroxy-3-methylbutan-2-one

Chapter 9 6

Naming Aldehydes

• IUPAC: Replace -e with -al.• The aldehyde carbon is number 1.• If -CHO is attached to a ring, use the suffix -

carbaldehyde.

Chapter 9 7

Examples

CH3 CH2 CH

CH3

CH2 C H

O

CHO

3-methylpentanal

2-cyclopentenecarbaldehydecyclopent-2-en-1-carbaldehyde

Chapter 9 8

Name as Substituent

• On a molecule with a higher priority functional group, C=O is oxo- and -CHO is formyl.

• Aldehyde priority is higher than ketone.

CH3 C CH

CH3

CH2 C H

OO

COOH

CHO

3-methyl-4-oxopentanal 3-formylbenzoic acid

Chapter 9 9

Common Names for Ketones

• Named as alkyl attachments to -C=O.• Use Greek letters instead of numbers.

CH3 C

O

CH

CH3

CH3 CH3CH C

O

CH

CH3

CH3

Br

methyl isopropyl ketone bromoethyl isopropyl ketone

Chapter 9 10

Historical Common Names

CH3 C

O

CH3

CCH3

O

C

O

acetone acetophenone

benzophenone

Chapter 9 11

Aldehyde Common Names• Use the common name of the acid.• Drop -ic acid and add -aldehyde.

– 1 C: formic acid, formaldehyde– 2 C’s: acetic acid, acetaldehyde– 3 C’s: propionic acid, propionaldehyde– 4 C’s: butyric acid, butyraldehyde.– 5 C’s: valeric acid, valeraldehyde

CH3 CH

Br

CH2 C H

O -bromobutyraldehyde 3-bromobutanal

αβγ

Chapter 9 12

Boiling Points• More polar, so higher boiling point than

comparable alkane or ether.• Cannot H-bond to each other, so lower

boiling point than comparable alcohol.

Chapter 9 13

Solubility

• Good 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.

Chapter 9 14

Formaldehyde

• Gas at room temperature.• Formalin is a 40% aqueous solution.

O

CO

C

OC

H H

H

H

H

H

heatH C

O

HH2O

H CH

OHHO

trioxane, m.p. 62C

formaldehyde,b.p. -21C formalin

Chapter 9 15

Industrial Importance

• Acetone and methyl ethyl ketone are important solvents.

• Formaldehyde used in polymers like Bakelite.

• Flavorings and additives like vanilla, cinnamon, artificial butter.

Chapter 9 16

Synthesis Review

• Oxidation– 2 alcohol + Na2Cr2O7 ketone

– 1 alcohol + PCC aldehyde

• Ozonolysis of alkenes.

Chapter 9 17

Synthesis Review (2)• Friedel-Crafts acylation

– Acid chloride/AlCl3 + benzene ketone

• Hydration of terminal alkyne– Use HgSO4, H2SO4, H2O for methyl ketone

Chapter 9 18

Aldehydes from Acid Chlorides

Use a mild reducing agent to prevent reduction to primary alcohol.

CH3CH2CH2C

O

HLiAlH(O-t-Bu)3CH3CH2CH2C

O

Cl

Chapter 9 19

Ketones from Acid Chlorides

Use lithium dialkylcuprate (R2CuLi), formed by the reaction of 2 moles of R-Li with cuprous iodide.

CH3CH2CH2Li2CuI

(CH3CH2CH2)2CuLi

(CH3CH2CH2)2CuLi + CH3CH2C

O

Cl CH3CH2C

O

CH2CH2CH3

Chapter 18 20

Nucleophilic Addition• A strong nucleophile attacks the

carbonyl carbon, forming an alkoxide ion that is then protonated.

• A weak nucleophile will attack a carbonyl if it has been protonated, thus increasing its reactivity.

• Aldehydes are more reactive than ketones.

Chapter 9 21

Addition of Water• In acid, water is the nucleophile.• In base, hydroxide is the nucleophile.• Aldehydes are more electrophilic since they

have fewer e--donating alkyl groups.

K = 2000C

H H

HOOH

H2O+H

C

O

H

K = 0.002C

CH3 CH3

HOOH

H2O+CH3

C

O

CH3

a gemdiol

a gemdiol

Chapter 9 22

Addition of Alcohol

Chapter 9 23

Mechanism

• Must 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.

Chapter 9 24

Mechanism for Hemiacetal

• Oxygen is protonated.• Alcohol is the nucleophile.• H+ is removed. =>

Chapter 9 25

Hemiacetal to Acetal

+

OCH3HO OCH3

H+

H+

HO OCH3

HOH+

OCH3CH3OOCH3CH3O

H

+

OCH3+

HOCH3

HOCH3

Chapter 18 26

Oxidation of AldehydesEasily oxidized to carboxylic acids.

Chapter 9 27

Cyclic Acetals

• Addition of a diol produces a cyclic acetal.• Sugars commonly exist as acetals or

hemiacetals.

O

CH2 CH2

HO OH+

O OCH2

CH2

Chapter 18 28

Tollens Test

• Add ammonia solution to AgNO3 solution until precipitate dissolves.

• Aldehyde reaction forms a silver mirror.

R C

O

H + 2 + 3 + 2+ 4+Ag(NH3)2+ OH

_ H2O2 Ag R C

O

O_

NH3 H2O

R C

O

H + 2 + 3 + 2+ 4+Ag(NH3)2+ OH

_ H2O2 Ag R C

O

O_

NH3 H2O

=>

SILVER MIRROR

Chapter 18 30

Reduction Reagents

• Sodium borohydride, NaBH4, reduces C=O, but not C=C.

• Lithium aluminum hydride, LiAlH4, much stronger, difficult to handle.

• Hydrogen gas with catalyst also reduces the C=C bond.

Chapter 18 31

Catalytic Hydrogenation

• Widely used in industry.• Raney nickel, finely divided Ni powder

saturated with hydrogen gas.• Pt and Rh also used as catalysts.

ORaney Ni

OH

H

TautormersConstitutional isomers in equilibrium with each other that differ in the location of a hydrogen atom and a double bond are called tautomers.

A case of tautomerization occurs with ketones (aldehydes) that are in equilibrium with their enol form, which are called keto enol tautomers

O OH

Keto Form Enol Form

ALDEHYDE AND KETONE REVIEW

Name

a. Cis-2-pentenalb. Cis-2-pentanalc. Trans-2-pentenald. Trans-2-pentanal

O

CHCH2

CHCH

H3C

Answer

a. Cis-2-pentenalb. Cis-2-pentanalc. Trans-2-pentenald. Trans-2-pentanal

The aldehyde is in position one. The double bond is trans.

Name

a. 2-Oxobutanoic acidb.2-Butanone-1-carbaldehydec. 2-Oxopentanoic acidd.3-Oxopentanoic acid

CH2

C CCH2 OH

OO

H3C

Answer

a. 2-Oxobutanoic acidb.2-Butanone-1-carbaldehydec. 2-Oxopentanoic acidd.3-Oxopentanoic acid

The carbon in the carboxylic acid is position one.

Identify the chemical name for acetone.

a. Methanalb.Ethanalc. Propanoned.Butanone

Answer

a. Methanalb.Ethanalc. Propanoned.Butanone

Acetone is called propanone or dimethyl ketone.

a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone

1. CH3CH2MgCl

2. H3O+

3. Na2Cr2O7, H2SO4

O

CHH3C

Answer

a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone

2-Butanone is formed in the Grignard reaction. The secondary alcohol is oxidized to a ketone with sodium dichromate.

a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone

O

COHH3C

1. CH3CH2Li

2. H3O+

Answer

a. 2-Propanoneb.2-Butanonec. 2-Pentanoned.3-Pentanone

The ethyl group adds to the carbonyl carbon.

a. 2,2-Diethoxypropaneb.2-Ethoxy-2-propanolc. Propane-2,2-diold.2-Ethoxypropane

O

CCH3H3C

2 CH3CH2OH

H+

Answer

a. 2,2-Diethoxypropaneb.2-Ethoxy-2-propanolc. Propane-2,2-diold.2-Ethoxypropane

Two molecules of ethanol are added to the carbonyl, with loss of water.

a. 1-Propanolb.Propanoic acidc. Propane-1,1-diold.1-Hydroxypropanoic acid

O

CHCH2

H3C1. Ag(NH3)2, -OH

2. H+

Answer

a. 1-Propanolb.Propanoic acidc. Propane-1,1-diold.1-Hydroxypropanoic acid

The Tollens reagent reduces an aldehyde to a carboxylic acid.

a. 2-Butanoneb.2-Butanolc. 2-Hexanoned.Butane

O

CCH3CH2

H3CNaBH4

CH3CH2OH

Answer

a. 2-Butanoneb.2-Butanolc. 2-Hexanoned.Butane

Butanone is reduced to 2-butanol.

Chapter 9 50

End of Chapter 9