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ALDEHYDES AND KETONES

STRUCTURE

They are characterized by the carbonyl functional group (C=O).

Carbonyl carbon is sp2 hybridized; trigonal planar;bond angles close to 120°.

R = alkyl or aryl group

Aldehydes and ketones undergo nucleophilic addition.

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Aldehydes are more reactive than ketones towards nucleophilic attack for both steric and electronic reasons.

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They are less reactive than acyl halides and acid anhydrides, but more reactive than esters, carboxylic acids, and amides.

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NOMENCLATURE

A. AldehydesCommon names are based on names of carboxylic acids; replace -ic acid by -aldehyde.

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NOMENCLATURE

A. Aldehydes

IUPAC names are based on longest chain containing the aldehyde group; name of parent ends in -al and aldehyde carbon is always C1.

A cyclic compound is named as a carbaldehyde.

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NOMENCLATURE

B. Ketones

Common names are generated by naming 2 groups attached to carbonyl carbon (alphabetically) and adding ketone.

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NOMENCLATURE

B. Ketones

IUPAC names are based on longest chain with the carbonyl group; name of parent ends in -one; number the chain in the direction that gives the lowest number to the carbonyl carbon.

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NOMENCLATURE

If other functional groups are present, priority order is:carboxylic acid > acid anhydride > ester > acid halide > amide > nitrile > aldehyde > ketone > alcohol > thiol > amine > ether > alkene > alkyne > halide.

3-oxobutanal

4-oxobutanoic acid3-methyl-2-cyclohexenone

3,3-dimethyl-2-butanone

2-hexanone

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PHYSICAL PROPERTIES

Boiling points and melting points are relatively moderate due to polarity of carbonyl group and lack of hydrogen bonding.

They are soluble in water up to 4-5 carbons since C=O group is H-bond acceptor. They are soluble in most common organic solvents.

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PREPARATION OF ALDEHYDES

A. Oxidation of Primary Alcohols

B. Ozonolysis of Alkenes

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PREPARATION OF ALDEHYDES

C. Reduction of Acid Chlorides or Esters

Mild reagents are used to prevent over-reduction.

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PREPARATION OF ALDEHYDES

C. Reduction of Acid Chlorides or Esters

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PREPARATION OF ALDEHYDES

C. Reduction of Acid Chlorides or Esters

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PREPARATION OF KETONES

A. Oxidation of Secondary Alcohols

B. Friedel-Crafts Acylation (Aromatic Ketones)

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PREPARATION OF KETONES

C. From Lithium Dialkylcuprates (Gilman Reagents)

Acid chlorides, which have the best leaving group (Cl¯) of the carboxylic acid derivatives, react with R’2CuLi to give a ketone as the product. Esters, which contain a poorer leaving group (¯OR), do not react with R’2CuLi.

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PREPARATION OF KETONES

D. From Hydration of Alkynes

Hydration of terminal alkynes in the presence of Hg2+ gives ketonesNot useful for internal alkynes because mixture results