Aldehydes and Ketones

Aldehydes - short form   -COH     or
Aldehydes can only be found on the very end of a molecule at the primary carbon. If you take a close look three of the four bonds on the aldehydes carbon are taken up with the oxygen and the hydrogen. Therefore there is only one bond left for bonding with another carbon and therefore it must be primary.
 
example     CH3CH3COH      propanal   or    propyl aldehyde

Be careful about spelling since a simple letter change results in a vastly different molecule. If the aldehyde is not important the group name changes to 'al' with the # of the appropriate parent chain carbon.
 
Ketone - can only be found on the inside of a molecule.
 
Why? As you can see only 2 of the carbon's bonds are used by attachment to the oxygen. Two bonds are available for bonding and to be a ketone these two must be attached to a carbon on each side, hence it must be inside a molecule. But what if one of these bonds is attached to a H? Then its an aldehyde and not a ketone.
 
                       propanone                                                                propanal

The ending "one" is added to the alkane name prefix. If the ketone is not important it's name switches to 'keto' and is treated just like any other substitution group.  The ketone is more important than an
alcohol and an aldehyde.          

Go to the Organic Aldehydes and Ketones Worksheet