Name as Substituent

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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.

COOH

CH

3

O

C

CH

3

CH CH

2

O

C H

CHO

3-methyl-4-oxopentanal

3-formylbenzoic acid

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4.5 Isomerism in aldehydes and ketones

• Aldehydes and ketones are constitutional isomers

• Aldehydes 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

4.6 Selected Common aldehydes and ketones

• Formaldehyde

• Acetone

• Vanillin

• Benzaldehyde

• Cinnamaldehyde

• Butanedione

Formaldehyde

• Gas at room temperature.

• Formalin is a 40% aqueous solution.

H

C

O

H

H

C

O

H

O

C

H

H trioxane, m.p. 62

C heat

O

H

2

O

H C H formaldehyde, b.p. -21

C

HO

OH

H C

H formalin

=>

Industrial Importance

• Acetone 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 -formalin

• Acetone – solvent and metabolic product

• Vanillin - vanilla flavoring

• Benzaldehyde - almond flavor

• Cinnamaldehyde - cinnamon

• Butanedione - butter

4.7 Physical properties

• Boiling points – page 121

• Solubility – water solubility page 123

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.

=>

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.

=>

4.8 Preparation of Aldehydes and

Ketones

• Oxidation

– 2

– 1

 alcohol + Na

2

Cr

2

O

7 alcohol

 aldehyde

 ketone

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