Chemistry Reference
In-Depth Information
Aldehydes
have the carbonyl group on the end of a carbon chain, and
ketones
have it somewhere other than the end. Because the end carbon atom
also has a hydrogen atom attached, the formal functional group for alde-
hydes is written:
O
X
±C±H
The systematic names of
al
dehydes end in -
al;
the systematic names of ket
one
s
end in -
one.
The simplest ketone, propanone, known familiarly as acetone, has
three carbon atoms. Because of its solvent properties, acetone is used in nail
polish remover. The simplest aldehyde, methanal, also known as formaldehyde,
is perhaps most familiar because it was formerly routinely used as a preserva-
tive for biological specimens.
O
X
O
X
HCHO
or
H±C±H
CH
3
COCH
3
or
CH
3
±C±CH
3
Methanal (formaldehyde)
Propanone (acetone)
The CO in the line formula for propanone must be
± C
O
because the total bond order of carbon is four.
Aldehydes and ketones are produced by the mild oxidation of alcohols.
If the group of the alcohol is on the end carbon atom, an aldehyde is
produced; if that functional group is on a carbon atom that is connected to
two other carbon atoms, a ketone is produced. Aldehydes and ketones can be
isomers of each other because both have the general molecular formula
C
n
H
2
n
O.
¬
OH
EXAMPLE 20.15
Draw condensed formulas for four aldehydes that are isomers of 2-pentanone.
Name these compounds.
Solution
The carbonyl group must be at the end of the carbon chain.
O
X
O
X
O
X
O
X
CH
3
W
HCCH
2
CH
2
CH
2
CH
3
HCCHCH
2
CH
3
HCCH
2
CHCH
3
HC±C±CH
3
CH
3
CH
3
CH
3
Pentanal
2-Methylbutanal
3-Methylbutanal
2,2-Dimethylpropanal
Practice Problem 20.15
Name and draw condensed formulas for the
three ketones that are isomers of pentanal.
