ALDEHYDES OR ALKANALS
The trivial names of aldehydes are derived from the names of the corresponding carboxylic acids (oxidation products of aldehydes) by replacing the suffix ic acid with aldehyde. Position of substituents in aldehyde chain, if any, is indicated by Greek letters a, f3, y, 8 etc. The a-carbon is one which is directly attached to the CHO group.
In IUPAC system, aldehydes are named by replacing ‘e’ from the corresponding name of alkane by suffix ‘ al’. Therefore, aldehydes are called alkanals.
In case of higher aldehydes, the longest carbon chain is chosen and is numbered in such a way that the aldehyde group is given number one. The names of few aldehydes are given in Table 45.2.
Table 45.2. IUPAC and Trivial Names of Some Alkanals
In these compounds the -CHO group is attached to the ring and therefore the ring name is followed by the word carbaldehyde. For example:
Aromatic aldehydes are of ‘two types:
(i) Aldehydes in which aldehydic group (-CHO) is directly attached to benzene ring. The simplest member of the family is named as benzaldehyde. Now, in case the substituents are attached in ortho, meta or para positions then such aldehydes are generally named as derivatives of benzaldehyde. Some examples are:
(ii) In second type of compounds, the aldehyde group is present in the side chain. For example,
The IUPAC names of some more aldehydes are discussed below in the form of bond line formulae:
According to 1993 Recommendations when three or more CHO groups are present in the compounds then all the aldehydic groups present in the compound are treated alike and the word carbaldehyde is used while writing the names. Some examples are discussed as follows:
KETONES OR ALKANONES
Ketones are represented by the general formula RCOR’. They are termed as simple ketones if both R and R’ are same alkyl groups. On the other hand, they are termed as mixed ketones if R and R’ are different. In common system, ketones are named by using the names of alkyl groups attached to carbonyl group followed by the word ‘ketone’.
In the case of substituted ketones the positions of substituents are indicated by Greek letters. a, 13. etc. (Trivial system) or numbers (IUPAC names).
According to the IUPAC system of naming compounds:
(i) The longest carbon chain carrying the carbonyl group is considered as the parent chain.
(ii) The chain is numbered from one end such that the carbonyl carbon is given the lowest possible number.
(iii) The name of the ketone is obtained by replacing ‘e ‘ of the parent alkane by ‘one’.
(iv) The positions of the carbonyl group and substituents are indicated by numbers. The names of some ketones are given in Table 45.3.
Table 45.3. Common and IUPAC Names of Some Ketones
Examples of some aromatic ketones are given below: