3.6: 3.22 Nomeclature of Aldehydes and Ketones

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Aldehydes and ketones contain the carbonyl group. Aldehydes are considered the most important functional group. They are often called the formyl or methanoyl group. Aldehydes derive their name from the dehydration of alcohols. Aldehydes contain the carbonyl group bonded to at least one hydrogen atom. Ketones contain the carbonyl group bonded to two carbon atoms.

Introduction

Naming Aldehydes

The IUPAC system of nomenclature assigns a characteristic suffix -al to aldehydes. For example, H₂C=O is methanal, more commonly called formaldehyde. Since an aldehyde carbonyl group must always lie at the end of a carbon chain, it is always is given the #1 location position in numbering and it is not necessary to include it in the name. There are several simple carbonyl containing compounds which have common names which are retained by IUPAC.

Also, there is a common method for naming aldehydes and ketones. For aldehydes common parent chain names, similar to those used for carboxylic acids, are used and the suffix –aldehyde is added to the end. In common names of aldehydes, carbon atoms near the carbonyl group are often designated by Greek letters. The atom adjacent to the carbonyl function is alpha, the next removed is beta and so on.

If the aldehyde moiety (-CHO) is attached to a ring the suffix –carbaldehyde is added to the name of the ring. The carbon attached to this moiety will get the #1 location number in naming the ring.

Summary of Aldehyde Nomenclature rules

Aldehydes take their name from their parent alkane chains. The -e is removed from the end and is replaced with -al.
The aldehyde funtional group is given the #1 numbering location and this number is not included in the name.
For the common name of aldehydes start with the common parent chain name and add the suffix -aldehyde. Substituent positions are shown with Greek letters.
When the -CHO functional group is attached to a ring the suffix -carbaldehyde is added, and the carbon attached to that group is C1.

Example 1

The IUPAC system names are given on top while the common name is given on the bottom in parentheses.

Naming Ketones

The IUPAC system of nomenclature assigns a characteristic suffix of -one to ketones. A ketone carbonyl function may be located anywhere within a chain or ring, and its position is usually given by a location number. Chain numbering normally starts from the end nearest the carbonyl group. Very simple ketones, such as propanone and phenylethanone do not require a locator number, since there is only one possible site for a ketone carbonyl function. The common names for ketones are formed by naming both alkyl groups attached to the carbonyl then adding the suffix -ketone. The attached alkyl groups are arranged in the name alphabetically.

Summary of Ketone Nomenclature rules

Ketones take their name from their parent alkane chains. The ending -e is removed and replaced with -one.
The common name for ketones are simply the substituent groups listed alphabetically + ketone.
Some common ketones are known by their generic names. Such as the fact that propanone is commonly referred to as acetone.

Example 2

The IUPAC system names are given on top while the common name is given on the bottom in parentheses.