Organic Functional Groups

FG3.  Simple Carbonyl Groups

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.


This site is written and maintained by Chris P. Schaller, Ph.D., College of Saint Benedict / Saint John's University (with contributions from other authors as noted).  It is freely available for educational use.

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Structure & Reactivity in Organic, Biological and Inorganic Chemistry by Chris Schaller is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License

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This material is based upon work supported by the National Science Foundation under Grant No. 1043566.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.


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