Aldehydes

Aldehydes are compounds that have carbon at the end of the chain making a double bond with an oxygen (carbonyl) and a bond with a hydrogen.

The methanal , in aqueous solution, is the formaldehyde (or formaldehyde) used in the preservation of cadavers and anatomical parts;

Ethanal (acetaldehyde or acetic aldehyde) is used in the synthesis of organic compounds, as in the preparation of ethanol, acetic acid and chloral (which is used as a hypnotic and leads to the formation of chloroform, which is an anesthetic, and DDT insecticide); in the reduction of silver salts in the manufacture of mirrors (Tollens’ reactive) and in obtaining resins;

Vanillin (3-methoxy-4-hydroxybenzenecarbaldehyde), extracted from the Vanilla planifolia orchid , is the active compound of the vanilla essence;

* Cinnamaldehyde imparts the characteristic flavor and odor of cinnamon.

These mentioned examples, despite having very different properties and being used in different applications, have something in common: they are all from the aldehyde group.

Aldehydes are all organic compounds that have the carbonyl group attached to a hydrogen, that is, this functional group always comes at the end of the carbon chain:

Aldehydes functional group

“R” represents any organic radical. If in the carbon chain there is only one COH group of the aldehydes, the compound is classified as monoaldehyde; but if there are two or more of that group, then it is a polyaldehyde.

As the examples above show, aldehydes of lower molar masses have a strong and irritating smell, but as the carbon chain grows, they start to have pleasant aromas. Methanal and other minor aldehydes are soluble in water because they make hydrogen bonds. However, the larger molecules are becoming increasingly insoluble in water, but are soluble in organic solvents such as alcohol, ether and benzene.

Despite making hydrogen bonds with water, thanks to the presence of carbonyl, aldehydes do not perform this type of interaction between their own molecules. Instead, they are attracted by intermolecular forces of the permanent dipole type.

Methanal and ethanal which have 1 and 2 carbons in the chain, respectively, are gases under ambient conditions. The rest are mostly liquid, and those with very high molecular mass are in solid form.

Don’t stop now … There’s more after the publicity;)

The nomenclature of aldehydes according to the official rules established by IUPAC is as follows:

Aldehyde nomenclature rule

Examples:

Nomenclature of unbranched aldehydes

Note that, unlike the other organic functions, it is not necessary to number the chain to indicate where the functional group indicated by the suffix “al” is coming from. This is because, as said, this functional group of aldehydes comes only from the carbon at the end.

However, the examples presented above are unbranched aldehydes, that is, they have only two free ends. In the case of branched or unsaturated aldehydes (double or triple bonds) in the carbon chain, it is necessary to choose the main chain and number the carbons.

The main chain will be the one that contains the functional group, the unsaturations and the largest amount of carbon atoms. If there is a tie, the chain with the most branches will be chosen. The carbon numbering starts from the carbon of the functional group:

Here are some examples:

Aldehyde nomenclature according to IUPAC rules

The usual nomenclature is made by writing the word “aldehyde” followed by the usual name of the corresponding carboxylic acid. But it is only used for normal (unbranched) and saturated aldehydes (which have only simple bonds between carbons).

Examples:

Usual nomenclature of normal and saturated chain aldehydes

Click here to see the nomenclature of carboxylic acids. To learn more details about the aldehydes mentioned at the beginning of this article and other compounds of this functional group, read the text “ Main daily aldehydes ”.

 

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