|
An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group.
 (Where -R represents the carbon chain.)
Structure
The aldehyde functional group is a carbonyl group bonded to a hydrogen atom and a carbon atom.
α carbon & α hydrogen An α (alpha) carbon is a carbon adjacent to a carbonyl group. An α hydrogen is a hydrogen atom bonded to the α carbon.
The pKa of an α hydrogen is 20.
Carbonyl group The other molecules containing a carbonyl group are: 
Aldehydes are named by IUPAC nomenclature by changing the suffix -e of the parent alkane to -al. Aldehydes can be produced by oxidation of primary alcohols. In the laboratory this may be achieved by heating the alcohol in an acidified solution of potassium dichromate, which is reduced to green Cr3+ during the reaction, or by the so called "Swern oxidation" ((CO)2Cl2 + (Me)2SO).
Aliphatic aldehydes are named as derivatives of their longest alkyl chain. Thus, HCHO is named as a derivative of methane, and CH3CH2CH2CHO is named as a derivative of butane. The suffix -al replaces the -e of the alkane name. Thus, HCHO is named methanal, more commonly known as formaldehyde, and CH3CH2CH2CHO is named butanal.
When a -CHO group is attached to a ring, the suffix -carbaldehyde is used. Thus, C6H5-CHO is known as benzenecarbaldehyde.
Physical properties The carbonyl group is polar.
Reactions
Synthesis - Reacting a primary alcohol with some oxidizing agents, such as pyridinium chloride, yields an aldehyde.
- Reacting an alkene with ozone will cause the bond to break if there is a vinylic hydrogen.
- Reacting an ester with DIBAL-H can cause reduction, yielding an aldehyde.
Common reactions - aldehyde + alcohol + acid or base ---> hemiacetal
- Treating aldehydes with oxidizing agents such as potassium permanganate, nitric acid, or chromium oxide, will yield a carboxylic acid.
- Treating aldehydes with Tollens' reagent (which is prepared by adding a drop of sodium hydroxide solution into silver(I) nitrate solution to give a precipitate of silver(I) oxide, and then add just enough dilute ammonia solution to redissolve the precipitate in aqueous ammoniato to produce [Ag(NH3)2]+ complex) will convert aldehydes to carboxylic acids without attacking carbon-carbon double bonds. See also oxidation of aldehyde (http://www.wiu.edu/users/mftkv/Chemistry102/oxidationaldehydes.html)
- Aldehydes can react with water to form Alcohol.
- Aldehydes can react with HCN to form cyanohydrins, R-C(H)(OH)(CN).
- Treating an aldehyde with a Grignard reagent can yield an alcohol with a substituted group from the Grignard reagent.
- Treating aldehydes with hydrazine will reduce a C=O bond to CH2 via the Wolff-Kishner reaction.
- aldehyde + nucleophile ---> tetrahedral carbonyl addition compound
Keto-enol tautomerism Equilibration of keto and enol tautomers is catalyzed by acid.
Oxidation & Reduction
Examples of Aldehydes
See also
| 
Feeds |
Contact