Aldehydes and ketones are organic compounds containing a carbonyl functional group, C=O. Carbon atoms in this group have two remaining bonds that may be occupied by hydrogen, alkyl, or aryl substituents. If at least one of these substituents is hydrogen, the compound is an aldehyde. If neither is hydrogen, the compound is a ketone.
Aldehydes and ketones contain carbonyl groups. Aldehydes are considered the most important functional groups. They are often called formyl or methanoyl groups. Aldehyde is a name derived from the dehydration of alcohol. Aldehydes contain carbonyl groups attached to at least one hydrogen atom. Ketones contain carbonyl groups attached to two carbon atoms.
Nomenclature of Aldehyde
The IUPAC nomenclature assigns the aldehyde-specific suffix -al. For example, H2C = O is methanal, well known as formaldehyde.
The aldehyde carbonyl group must always be at the end of the carbon chain, so it is always numbered 1 and does not need to be included in the name.
There are some simple carbonyl-containing compounds with common names retained by IUPAC.
There is also a common way to name aldehydes and ketones. Aldehydes use the same common backbone names used for carboxylic acids, with the suffix – aldehyde added to the end.
In the common name for aldehydes, carbon atoms near carbonyl groups are often indicated in Greek letters.
The atom next to the carbonyl function is alpha, the next atom is beta, and so on.
If the aldehyde portion (-CHO) is added to the ring, the suffix – carb aldehyde is added to the ring name.
The carbon bonded to this part is given position number 1 when naming the ring.
Rules - Aldehyde Nomenclature
Aldehyde is named after its parent alkane chain. The last -e is removed and replaced with -al.
The aldehyde functional group is numbered 1 and this number is not included in the name.
The common name for the aldehyde starts with the common name for the parent chain and adds the suffix -aldehyde.
The positions of the substituents are marked in Greek letters.
If the functional group -CHO is attached to the ring, the suffix -carbaldehyde is added and the carbon attached to that group is C1.
Nomenclature of Ketones
The IUPAC nomenclature assigns the ketone-specific suffix -1.
The carbonyl functional group of the ketone can be anywhere in the chain or ring.
Its position is usually indicated by a position number.
Chain numbering usually begins at the end closest to the carbonyl group.
Very simple ketones, such as propanone and phenyl ethanol, do not require a locator number because they have only one possible site for the carbonyl functional group of the ketone.
The common name for a ketone is formed by naming both alkyl groups attached to the carbonyl and then adding the suffix - ketone.
The added alkyl groups are listed in alphabetical order by name.
Rules - Ketone Nomenclature
Ketones are named after their parent alkane chains.
The -e suffix is removed and replaced with -one.
The common name for ketones is the substituents + ketones listed in alphabetical order.
Some common ketones are known by their common name.
Like the fact that propanone is commonly called acetone.
Aldehyde and Ketone Naming in the Same Molecule
Like many molecules with 2 or more functional groups, one is preferred and the other is named as a substituent.
Aldehydes have a higher priority than ketones, so molecules containing both functional groups are called aldehydes, and ketones are called "oxo" substituents.
Aldehyde functional groups do not need to be position numbered, but ketones usually need to be position numbered.
Naming of Cyclic Ketones and Diketones
In cyclic ketones, position 1 is assigned to the carbonyl group and this number is not included in the name unless there are multiple carbonyl groups.
The rest of the ring is numbered to give the substituents the lowest possible position number.
Note that the Cyclo prefix precedes the parent chain name to indicate that it is a ring.
As with other ketones, the end of -e is replaced by the end of -eins to indicate the presence of the ketone.
For cycloalkanes containing two ketones, both carbonyls must be position numbered.
Also, the trailing -e is not removed, but the suffix -dion is added.
Carbonyl and Alkene Nomenclature within the Same Molecule
If an aldehyde or ketone is present in a molecule that also contains an alkene functional group, the IUPAC naming scheme prefers carbonyl.
This means that the carbonyl will be given the lowest possible place number and the appropriate nomenclature suffix will be added.
If the carbonyl is contained in the alkene, the following order is followed:
(alkene position number)-(longest carbon chain prefix name minus trailing -an)-(tailing -en is alkene)-(carbonyl position number if ketone is present) ) (One of the -one- or -anal ends).
Note that you should specify the lowest possible position number, as carbonyl takes precedence.
Also, include the alkene cis / tran or E / Z nomenclature as needed.
The chemistries of aldehydes and ketones are influenced by the presence of carbonyl groups in them. In aldehydes, the carbonyl group is attached to one carbon and hydrogen, whereas in ketones, it is attached to two carbon atoms.
In other words, the remaining two bonds of the carbon atom of the carbonyl group are occupied by hydrogen, alkyl, or aryl substituents. If any of the substituents are hydrogen, the compound is called an aldehyde, and if none of them are hydrogen, it is a ketone.