ALDEHYDES AND KETONES

 

Reference: McMurry Ch 9 George et al Ch 2.6

 

Structure and bonding

 

 

 

Nomenclature

Aldehydes

 

Ketones

 

Reactions of Aldehydes and Ketones

 

With the exception of oxidation of aldehydes, the reactions of aldehydes and ketones is dominated by nucleophilic addition.

 

1. Oxidation of aldehydes

 

Example:

 

2. Nucleophilic addition

 

 

In summary

 

 

Examples: Grignard reaction

 

Recap generation of a Grignard reagent from an alkyl halide and magnesium in dry diethyl ether solvent

 

 

Grignard reagents also react with carbon dioxide to generate carboxylic acids after addition of aqueous H+

 

Reduction

Reduction of the non-polar C=C or C C bonds in alkenes and alkynes respectively, can be accomplished with (non-polar) hydrogen gas, H2. The polar C=O group requires a polar source of hydrogen: H- / H+. The hydride ion (H-) is supplied by a metal hydride, LiAlH4 or NaBH4 and the H+ by an aqueous acid "quench".

 

 

Addition of alcohols

Alcohols add to aldehydes and to ketones to form hemiacetals. When an aldehyde or ketone is dissolved in an alcohol solution, the free carbonyl compound is in equilibrium with its hemiacetal derivative.

Typically the equilibrium strongly favours the free aldehyde or ketone except when an aldehyde or ketone can react intramolecularly (i.e. within the same molecule). If a 5- or 6-membered ring is formed then the cyclic hemiacetal is the major species in the equilibrium.

 

Carbohydrates

 

Example: Glucose

 

 

Some biologically active compounds containing a

carbonyl functional group:

 

 

 

 

Questions on Aldehydes and Ketones

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