Structure and Naming of
ALDEHYDES & KETONES
Brown's GCE A Level AS A2 Chemistry Revising
Advanced Level Organic Chemistry
Part 5 CARBONYL COMPOUNDS - ALDEHYDES and KETONES
5.1 The molecular structure and naming of ALDEHYDES and KETONES -
including nomenclature of some isomers
Nomenclature of aldehydes & ketones names and
structures of aldehydes & ketones How to name aldehydes? How to name ketones?
Nomenclature of substituted aldehydes or ketones - examples of acceptable names, displayed formula of aldehydes and
formula of aldehydes and ketones, molecular formula of aldehydes and ketones, skeletal formula
of aldehydes and ketones, structural formula of aldehydes and ketones and
homologous series of aldehydes and ketones, how to name the carbonyl group of compounds known as
aldehydes and ketones
Chemistry Part 5 sub-index: 5.1.1 Nomenclature
introduction * 5.1.2 Examples of aldehydes
5.1.3 Examples of ketones * 5.1.4 Other
examples of substituted ketones
5.1.5 Oxidation sequence: alcohol ==>
aldehyde/ketone ==> carboxylic
Other advanced level
organic chemistry links
Revision notes on the
structure and naming-nomenclature of Aldehydes and Ketones
5.1.1 Introduction to Aldehyde and Ketone Nomenclature
- How do you name aldehydes? How do you name
ketones? How do you name substituted aldehydes or ketones?
Aldehydes and ketones are a group of compounds containing the
carbonyl group, C=O.
Aldehydes always have a hydrogen atom attached to the carbon of the carbonyl group, so the functional group is
-CHO (see diagram above).
- The functional group is shown by using 'al' in the suffix part of the name
e.g. methanal, ethanal, propanal etc.
- The prefix for the aldehyde name is based on the
parent alkane minus the e.
- No number is required for the aldehyde group
because the aldehyde group cannot be anything else except carbon atom 1.
- A number would only be required if a
higher ranking group is present e.g. a -COOH carboxylic acid group.
Ketones always have two carbon atoms attached to the carbon atom of the carbonyl group, so the functional group is
C-CO-C (see diagram above).
- The prefix for the ketone name is based on the
parent alkane minus the e.
- The functional group is shown by using 'one' in the suffix part of the name
e.g. propanone, butanone, hexan-3-one etc.
- A number to denote the position of the ketone
group is definitely required beyond butanone and although not strictly needed
for butan-2-one, since only one ketone position is possible, it is required for
substituted butanones and beyond.
- The substituent numbers are based on giving the
carbonyl C=O carbon the lowest number
e.g. 2-methylbutanal ('al' position = 1). The number position of the C=O group in ketones needs to be specified for carbon chains of over 4, or less, if substituents present
e.g. 3-methylbutan-2-one, heptan-2-one, heptan-3-one and heptan-4-one (there is no heptan-1-one, this is
- For the same 'carbon number', aldehydes and
ketones are structural and functional group isomers based on e.g. for
aliphatic carbonyl compounds CnH2nO.
- Some 'old' names are quoted in (italics) though their
use should be avoided if possible [but many still used - just put one into
5.1.2 Examples of Aldehydes
(formaldehyde), , ,
Methanal is a trigonal planar
shape and the planarity gives H-C=O and H-C-H bond angles of 120o.
(acetaldehyde), , , ,
Bond angles from left to right:
H-C-C 109o, C-C=O 120o, C-C-H 120o and
(propionaldehyde), , , ,
(2 not strictly needed but advisable,
(butyraldehyde), , ,
(old name 'valeraldehyde'), ,
5.1.3 Examples of ketones
(acetone, dimethyl ketone,
DMK), , , ,
Bond angles: The trigonal
planarity around the carbonyl group >C=O gives a C-C=O and C-C(=O)-C of 120o
and associated with the methyl group, the H-C-C and H-C-H bond angles are
(or butan-2-one, but 2 not strictly
needed, methyl ethyl ketone, MEK, 2-butanone),
(2 and 3 not strictly needed BUT
(2-pentanone), , ,
(3-pentanone), , ,
5.1.4 Other examples of
substituted ketones e.g.
iodoketones and phenylketones
1 to 3, 5 to 6 and 10 are
formed by the reaction of the parent ketone with iodine in the
presence of an acid (e.g. HCl(aq), because H+(aq)
catalyses the reaction)
iodopropanone (1-iodopropanone, 1- not really needed)
(1-iodobutan-2-one, -2- not really needed, 1-iodo-2-butanone)
(3-iodobutan-2-one, -2- not really needed, 3-iodo-2-butanone)
(4-iodobutan-2-one, -2- not really needed, 4-iodo-2-butanone)
(-2- needed, 1-iodo-2-pentanone)
(-2- needed, 3-iodo-2-pentanone)
(-2- needed, 4-iodo-2-pentanone)
(-2- needed, 5-iodo-2-pentanone)
(-3- needed, 1-iodo-3-pentanone)
(-3- needed, 2-iodo-3-pentanone)
5.1.5 Alcohol oxidation
can be readily oxidised
to aldehydes and ketones and aldehydes are easily oxidised further to carboxylic
The reagent can be potassium dichromate(VI) K2Cr2O7
, acidified with diluted sulphuric acid H2SO4(aq)
(colour change is orange to green).
For details of the practical method and
full equations see
Organic Redox Reactions
However the oxidation products depend on the original structure of the alcohol. The alcohol functional group -OH in aliphatic alcohols is classified into primary, secondary and tertiary types (see below). When the -OH is attached directly to a benzene ring the molecule is called a phenol.
Primary aliphatic alcohols R-OH, R is H or alkyl: When oxidised they form aldehydes and then further oxidation gives a relatively stable carboxylic acid e.g.
Secondary aliphatic alcohols
R-CH(OH)-R', R or R' are both alkyl (can be aryl): When oxidised they form relatively stable ketones (see NOTE below) e.g.
==> butanone (butan-2-one)
Tertiary aliphatic alcohols RR'R"C-OH,
where R,R' or R" are all alkyl (or aryl): These are relatively stable to oxidation (see NOTE
1. further down) e.g.
carboxylic acids are relatively stable to further oxidation because a strong C-C
bond must be broken in the process. Prolonged oxidation with H2SO4(aq)/K2Cr2O7
or using a more powerful oxidising agent, results in the formation of carbon
dioxide, water and carboxylic acids of shorter carbon chain length than the
original alcohol or ketone.
When a primary alcohol
is oxidised to an aldehyde, the oxidation to the carboxylic acid is rapid. If
the aldehyde formed first is the desired product, it must be immediately
distilled off to prevent further oxidation.
LINKS TO ASSOCIATED ADVANCED ORGANIC CHEMISTRY PAGES
Multiple choice quiz on naming aldehydes or ketones
Type in name
(short answer) quiz on aldehydes and ketones
10.6.1 Carbonyl compounds - ALDEHYDES and
KETONES - introduction to their reactions and reaction mechanism
Nucleophilic addition of
hydrogen cyanide to aldehydes & ketones to form a hydroxy-nitrile
10.6.3 Addition of hydrogen to aldehydes and ketones -
reduction with LiAlH4 or NaBH4
to give alcohols
10.6.4 Iodination of ketones e.g.
a 2-one like propanone (a methyl ketone) to give iodo-ketones
All Advanced Organic
Summary of Organic Functional Groups Notes
Quiz on Organic Structure Recognition
Summary of organic
chemistry functional group tests
Intermolecular forces & boiling points of
aldehydes & ketones compared to other
and bond angles of simple organic molecules
formula keywords: how to name
naming nomenclature empirical molecular formula graphic formula displayed
formula skeletal formula structural isomers isomerism 5.1.1 carbonyl compounds Nomenclature
introduction * 5.1.2 Examples of aldehydes * 5.1.3 Examples of ketones * 5.1.4
Other examples of substituted ketones CH2O HCHO C2H4O CH3CHO
CH3CH2CHO CH3-CH2-CHO CH3COCH3 CH3-CO-CH3 C4H8O CH3CH2CH2CHO CH3-CH2-CH2-CHO CH3COCH2CH3
CH3-CO-CH2-CH3 C5H10O CH3CH2CH2CH2CHO
CH3COCH2CH2CH3 CH3CH2COCH2CH3 C7H6O C6H5CHO C6H5COCH3