Structure and Physical Properties
Aldehydes and ketones are polar compounds.
The carbonyl carbon is partially positive (?+) and
the carbonyl oxygen is partially negative (?-).
Aldehydes and ketones have higher melting and boiling points than hydrocarbons of equivalent molecular weight. This is due to the attraction between molecule due to the polarity of the carbonyl group. This type of attraction is referred to as dipole-dipole forces of attraction.
IUPAC Rules for Naming Aldehydes
1. Determine the parent hydrocarbon.
2. Replace -e with ľal.
3. Number the carbon chain with the carbonyl group as number one.
IUPAC and Common names of Aldehydes
|Methanal (formaldehyde)||Ethanal (acetaldehyde)|
|Propanal (propionaldehyde)||Butanal (butyraldehyde)|
The common names of the aldehydes are derived from the
same Latin roots as the corresponding carboxylic acids. In the common system
of nomenclature, substituted aldehydes are named as derivative of the straight-chain
Greek letters are used to indicate the position of the substituents.
2-Phenylbutanal = a-phenylbutyraldehyde
3-Methylpentanal = b-methylvaleraldehyde
IUPAC Rules for Naming Ketones
1. Determine parent hydrocarbon.
2. Replace -e with -one.
3. Carbonyl carbon is numbered as lowest possible value.
|Propanone (acetone)||Butanone (methyl ethyl ketone)
Common Aldehydes and Ketones
(The following information was obtained at: http://www.bartleby.com.)
Formaldehyde (methanal) is a colorless gaseous compound, HCHO, the simplest aldehyde, used for manufacturing melamine and phenolic resins, fertilizers, dyes, and embalming fluids and in aqueous solution as a preservative and disinfectant.
Acetaldehyde (ethanal) is a colorless, flammable liquid, C2H4O, used to manufacture acetic acid, perfumes, and drugs. Also called aldehyde.
Acetone (propanone) is a colorless, volatile, extremely flammable liquid ketone, CH3COCH3, widely used as an organic solvent.
Benzaldehyde is a normally colorless aromatic oil, C6H5CHO,
obtained naturally, as from the bitter almond, or made synthetically and
used in perfumes and as a solvent and a flavoring.
Reactions of Aldehydes and Ketones
Preparation of Aldehydes and Ketones
1o alcohol ------> Aldehyde
2o alcohol ------> Ketone
3o alcohol ------> NR
Methanol -----> Methanal
Aldehydes are easily oxidized to carboxylic acids, whereas ketones do not generally undergo further oxidation.
Tollen's Test for Aldehydes
Aldehyde + AgNO3 + NaOH + NH3 ---> RCO21-Na1+ + Ag
Benedict's or Fehling's Test for Aldehydes
Aldehyde + [Cu2+complex] --> RCO2H + Cu2O
If a carbonyl compound is treated with excess alcohol in the presence of a trace of acid, aldehydes will give an acetal product, whereas ketones will give a ketal product.
All molecule of this general type will be classified as acetals.
Carbonyl compounds with one or more hydrogens on their a-carbons rapidly interconvert with their corresponding enols.
The aldol condensation is a reaction in which aldehydes and ketones react to form larger molecules. A new carbon-carbon bond is formed.
In this generalized reaction the a-carbon of one aldehyde forms a bond with the carbonyl carbon of the other aldehyde.
2 Acetaldehyde + Sodium ethoxide ---> Aldol (a b-hydroxy aldehyde)