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Aldehydes and Ketones

Aldehydes and Ketones. Structure. They are characterized by the carbonyl functional group (C=O). Carbonyl carbon is sp 2 hybridized; trigonal planar ; bond angles close to 120 °. R = alkyl or aryl group. Aldehydes and ketones undergo nucleophilic addition.

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Aldehydes and Ketones

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  1. 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.

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

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

  4. Nomenclature A. Aldehydes Common names are based on names of carboxylic acids; replace -ic acid by -aldehyde.

  5. 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.

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

  7. 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.

  8. 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.

  9. 3-oxobutanal 2-hexanone 3,3-dimethyl-2-butanone 3-methyl-2-cyclohexenone 4-oxobutanoic acid

  10. 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.

  11. Preparation of Aldehydes A. Oxidation of Primary Alcohols B. Ozonolysis of Alkenes

  12. Preparation of Aldehydes C. Reduction of Acid Chlorides or Esters Mild reagents are used to prevent over-reduction.

  13. Preparation of Aldehydes C. Reduction of Acid Chlorides or Esters

  14. Preparation of Aldehydes C. Reduction of Acid Chlorides or Esters

  15. Preparation of Ketones A. Oxidation of Secondary Alcohols B. Friedel-Crafts Acylation (Aromatic Ketones)

  16. Preparation of Ketones 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.

  17. Preparation of Ketones D.From Hydration of Alkynes Hydration of terminal alkynes in the presence of Hg2+ gives ketones Not useful for internal alkynes because mixture results

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