Simple carbonyl groups contain a carbon double bonded to an oxygen. That C=O unit is commonly called a carbonyl. However, the carbonyl carbon is attached either to two carbons, in which case the compound is called a ketone, or to a carbon and a hydrogen, in whch case the compound is called an aldehyde. If the carbonyl carbon is attached to other heteroatoms, such as oxygen, nitrogen or a halogen, then it is called a carboxylic acid derivative or a carboxyloid.
It is useful to know the names of the normal (straight-chain) hydrocarbons, in which straight chains of hydrocarbons are connected by single bonds and the carbons' valences are saturated with hydrogens. The names of these compounds form the root names of other compounds having the same number of carbon atoms in a continuous chain.
| Number of carbons | Name |
| 1 | meth |
| 2 | eth |
| 3 | prop |
| 4 | but |
| 5 | pent |
| 6 | hex |
| 7 | hept |
| 8 | oct |
| 9 | non |
| 10 | dec |
The names of these compounds are based on the names of alkanes, but the suffix of the name varies to indicate the functional group present.
| Class | Icon | Description | Suffix |
| Ketone | R(CO)R | contains C=O connected to two carbon | one |
| Aldehyde | RCHO | contains C=O connected to one carbon and one hydrogen | al |
The following scheme provides representative examples of aldehydes and ketones as well as a brief guide to how the formal names of these compounds are put together based on their structures. Note that the root name is based on the longest continuous chain that contains the functional group. Substituents are named according to how many carbons they contain in a straight chain, and numbered based on where they are found along the main chain, in which each carbon can be numbered from one end to the other. The main functional group is present is always given the lowest possible number. If more than one functional group is present, the one that contains the most bonds to oxygen usually gets priority.
Note that, if more than one of the same type of substituent are present, a prefix is used to tell how many of them are present.
| Number | Prefix |
| 2 | di |
| 3 | tri |
| 4 | tetra |
| 5 | penta |
| 6 | hexa |
| 7 | hepta |
Problem FG3.1.
Provide structures for the following aldehydes and ketones.
a) pentanal b) hexanal c) propanal
d) 3-nonanone e) 5-methylheptanal f) 2,2-dimethylheptan-4-one
g) (E)-5-methyloct-2-en-4-one h) 3,4-dimethylhex-5-en-2-one i) (Z)-4-methyloct-6-en-3-one
Problem FG3.2.
Provide names for the following aldehydes and ketones.
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Structure & Reactivity in Organic, Biological and Inorganic Chemistry by
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