1.3 Aldehydes and Ketones

LEARNING GOALS

After   Chapter 1.3,    you will    be  able    to:

Distinguish aldehydes   from    ketones

Recall  common  names   for methanal,   ethanal,    propanal,   and propanone

Determine   the highest priority    functional  group   in  a   complex molecule

Apply   appropriate prefixes    and suffixes    when    naming  molecules   containing  aldehyde    and

ketone  groups

Aldehydes and ketones are two classes of molecules that contain a carbonyl group, which is a
carbon double-bonded to an oxygen. Aldehydes and ketones differ in the placement of the carbonyl
group: aldehydes are chain-terminating, meaning that they appear at the end of a parent chain,
while ketones are found in the middle of carbon chains. Aldehydes and ketones do not have any
leaving groups connected to the carbonyl carbon; they are only connected to alkyl chains or, in the
case of aldehydes, hydrogen atoms. As we’ll examine later, carboxylic acids and their derivatives do
contain leaving groups connected to the carbonyl carbon.

ALDEHYDES

Aldehydes have a carbonyl group found at the end of the carbon chain. Because this is a terminal
functional group that takes precedence over many others, it is generally attached to carbon number

1. Aldehydes are named by replacing the –e of the parent alkane with the suffix –al. When the
   aldehyde is at position 1, as is usually the case, we do not need to include this number in the
   chemical name. Figure 1.7 shows the IUPAC nomenclature for two aldehydes.