6.1 Introduction
Carbonyl compounds are compounds that contain the carbonyl group, which include aldehydes, ketones, carboxylic acid and its derivatives.

They have dipolar moment as oxygen is more electronegative than carbon. This implies that the carbonyl carbon is slightly positively charged and the carbonyl oxygen is slightly negatively charged.  This makes the former susceptible to nucleophilic attack while the latter should be susceptible to attack by electrophiles.

In simple nucleophilic addition reaction, where the rate limiting step is the attack by nucleophile (Nu-), the rate of the reaction will reduce with electron donating R groups and enhance with electron withdrawing R groups. This is on account of the fact that the positive charge on carbonyl carbon is neutralized progressively on going to the transition state for nucleophilic addition.

Thus it is further expected that the factors which may cause the delocalization of the positive charge on the carbonyl carbon will render the nucleophilic addition slow. Such factors include conjugation with aromatic rings, double bonds and groups containing unshared pair of electrons. As the addition reaction proceeds, the trigonal carbon is converted to saturated carbon, any increase in steric bulk in the R groups is expected to hinder the rate of the reaction. Thus, carbonyl compounds containing sterically bulky groups tend to react slowly and more reversibly.

6.2 Aldehydes and Ketones
Trivially, aldehydes are usually named after the acids they form on oxidation. The –ic in the name of the acid is then replaced by aldehyde to get the name of the aldehyde.

On the other hand, ketones are named by using the names of the groups attached with the carbonyl group and then adding ketone after the name of groups.

In the IUPAC system, aldehydes and ketones are named according to the following procedure:

• The name of the parent hydrocarbon (alkane or alkene or alkyne) is determined while counting the carbonyl carbon as a methyl group for aldehydes and as a methylene group for ketones. The substituents are named as it is done for the hydrocarbon while considering the position of aldehyde as 1-position. For both aldehydes and ketones, the naming is done as in alkanes but keeping in mind the priority sequence and rule of lowest locants.
• The name of the alkane is modified to alkanal for an aldehyde. In case of ketones, the name is modified to alkanone. The position of the carbonyl group is denoted as numerical prefix to –one.

  

• In cases where both the aldehyde and keto functionalities are present in the same molecule, the aldehyde gets preference and the molecule is suffixed with an –al. The position of the keto group is denoted by a numerical prefix and is denoted by used of the word oxo.