Topic: Functional Group #5-Aldehydes
Do Now: Write the
molecular formula for
the two sugars on the
right. Are they
isomers?
O

• General formula: RCH or RCHO
• Carbonyl group just like ketone except
always at end of aldehyde
– Attached to Carbon chain on one side and a
H on the other
Properties = same as ketones
O
R
C=O
+

H
-
R
C=O
+

H
-
H
Aldehydes are polar! Dissolve in water
Dipole-Dipole interactions
Boiling point:
higher than alkanes (same # C’s)
+
-
H
Acetaldehyde (ethanal) = important
aldehyde
• Occurs naturally in
• Coffee
• Bread
• Ripe fruit
• Produced by plants
• Produced by the partial oxidation of ethanol in the
liver and may be a contributing factor to hangovers
from alcohol consumption
• It’s an air pollutant resulting from combustion (car
exhaust and cigarette smoke)
Flavoring agents
Naming
• Find name of alkane with same # of C’s
– change the -e to -al
• Never need #’s for aldehydes
– b/c functional group always on end C

O
HCH
Methanal
common name = formaldehyde
O

H
HCCH
H
Ethanal
common name = acetaldehyde
CH3CH2CH2CHO
CHO ending indicates aldehyde
4 Carbons so base name is butane
Drop -e and add al  butanal