Ch. 13 – Aldehydes and Ketones
The functional group common to both aldehydes and ketones is the carbonyl group, a C
atom with a double bond to a O atom.
This group tends to undergoes addition reactions (like what we saw with alkenes with the –
C=C- bond), as this group is highly polar.
For ketones, two carbon-containing groups (2 alkyl, 2 aryl, or 1 alkyl and 1 aryl) are
attached to the carbonyl group, so the general formulas are:
R—CO—R’, Ar—CO—R, Ar
For aldehydes, one group attached to the carbonyl is instead a H atom, so the general
H—CHO, R—CHO, Ar—CHO.
[When writing condensed structural formulas, one writes aldehydes with –CHO vs –COH to
avoid confusion with alcohols. In both –CO- and –CHO, the C to O double bond is implied.]
These two families of compounds have some common properties since they share the
carbonyl group, but will also show differences in certain types of reactions (e.g., oxidation).
Nomenclature for Aldehydes (sect. 13.2)
Common names are used for the smaller aldehydes, typically taken from the acids that the
aldehydes are oxidized to.
Examples are HCHO (formaldehyde) from HCOOH (formic
acid), and CH
CHO (acetaldehyde) from CH
COOH (acetic acid).
(Know these two.)
The IUPAC names of aldehydes are derived from corresponding alkanes, where the LCC
with the –CHO group is chosen, the
is dropped from the alkane and the ending
This group takes precedence, so the carbonyl carbon is always Carbon-1 in the
numbering of the LCC so it isn’t necessary to be designated.
(This is different from
alkenes, alkynes, alcohols, where the location of either the double bond, triple bond, or –OH
group must be named.)
Note the smells of vanilla, almonds, lemongrass, and cinnamon comes from aldehydes (see
Fig. 13.3 on p. 425)!
Naming Common Ketones (section 13.2)