Aldehydes and Ketones:
These differ only in that the C=O is terminal on the aldehyde and not at the end on the ketone.
Naming the aldehyde, replace the 'ane' of the alkane with 'al' .
O
H C
H
Formaldehyde or methanal
is a well known biological preservative, "eau de shark"
The shortest chain ketone is acetone, know in IUPAC as propanone
H
H
H C
H
C C H
O H
ALDEHYDES AND KETONES: These are organic compounds that contain a carbonyl group. It the
group is terminal, the compound is classified as an aldehyde; otherwise it is a ketone.
Naming an aldehyde:
1. Name the parent alkane. Always give the carbon atom of the carbonyl group the position
number 1.
2. Replace the –e at the end of the alkane name with –al. Because the carbonyl group is always
given position number 1, you do not need to include a position number for the carbonyl group.
3. When the CHO is attached to a cyclic hydrocarbon, the CHO is given the name
-carbaldehyde. Below is cyclohexane carbaldehyde and the carbon with the CHO is numbered
1 in the cyclo chain
Naming a ketone:
1. Name the parent alkane. Note that the main chain must contain the C=O group.
2. Replace the –e suffix with -one
3. If more than one ketone group is present, keep the –e suffix and add – dione, -trione, etc.
4. For carbon chains larger than 4, a position number is needed for the carbonyl group.
Indicate the position of the C=O as you did the position of a double bond in and alkene and the
OH in an alcohol. The carbon where the =O is must be closest to the 1 end of the ketone.
H H CH3
H C C C C CH3
H H H O
3-methyl pentan-2-one is
*** if an aldehyde and ketone are present – treat the =O of the ketone as an –oxy functional
group and the Aldehyde as the parent.
Properties of Aldehyde and Ketones: The C=O bond makes aldehydes and ketones polar
molecules. There is no hydrogen bonding with these molecules as there is no –OH group. They
can however accept hydrogen bonding from water. But there are dipole-dipole attraction
between the polar C=O bonds. So, molecules of aldehydes or ketones attract each other more
strongly than alkanes with the same molar mass, but less than alcohols of the same size.
In general the odour of aldehydes is strong and pungent, while that of ketones is sweet. But
higher molecular mass aldehydes have pleasant smells and are often used in perfumes.
Reactions of aldehydes and ketones. (Draw 2 examples)
Alcohols can be reacted in the presence of an oxidizing agent (Cr2O72- + H2SO4) to form an
aldehyde or a ketone, depending upon whether the alcohol is primary or secondary.
example #1 1 alcohol  aldehyde
example #2
2o alcohol  ketone
When you oxidize with H2SO4 as a catalyst, the reaction can be thought of as adding O and
removing H2O . This gives a net elimination of H2
Alcohols will also react with acidic Cr2O72- to produce Cr3+ and an aldehyde. (the first
Breathalyzer)
Physical property summary Guide
There are three types of intermolecular attractive forces that help explain the physical properties
like relative melting point, boiling point and solubility of organic compounds:
Name
Origin
Type of compounds
Result on physical properties
1. London
(dispersion)forces
Non-uniform motion
of electrons
in atoms and
molecules
Alkanes/alkenes/Alkynes
Low PB/BP.
More atoms = stronger force
= higher BP/MP
2. Dipole-dipole
interactions
Electrostatic
attraction between
(+) and (-) ends of
molecules
3. Hydrogen
bonding
An especially strong
sort of dipole-dipole
interaction
Homework: 1-5 p. 46
all molecules having polar
covalent bonds or POLAR shapes
Aldehydes/Ketones
...molecules having H atom(s)
covalently bound to N,O, or F
Alcohols, NH2, COOH have it
Aldehydes/ketones
DO NOT
Raises MP/BP
Makes soluble in water
More polar = more soluble = higher BP?MP
Raises Solubility and MP/BP