Nomenclature of Aldehydes and Ketones

Systematic names for aldehydes are derived by replacing the final -e of the alkane name with -al. An aldehyde carbon is at the end of a chain, so it is number 1. If the aldehyde group is attached to a large unit (usually a ring), the suffix carbalclehyde is used. 

A ketone or aldehyde group can also be named as a substituent on a molecule with another functional group as its root. The ketone carbonyl is designated by the prefix OXO-, and the —CHO group is named as a formyl group. Carboxylic acids frequently contain ketone or aldehyde groups named as substituents. 

Some ketones have historical common names. Dimethyl ketone is always called acetone, and alkyl phenyl ketones are usually named as the acyl group followed by the suffix -phenone. 

Common names of aldehydes are derived from the common names of carboxylic acids (Table 18-2). These names often reflect the Latin or Greek term for the original source of the acid or the aldehyde. Greek letters are used with common names of aldehydes to give the locations of substituents. The first letter (a) is given to the carbon atom next to the carbonyl group. 

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Structure of the Carbonyl Group 817 18-3 Nomenclature of Ketones and Aldehydes 818 18-4 Physical Properties of Ketones and Aldehydes 820 18-5 Spectroscopy of Ketones and Aldehydes 822 18-6 Industrial Importance of Ketones and Aldehydes 828 18-7 Review of Syntheses of Ketones and Aldehydes 829 18-8 Synthesis of Ketones from Carboxylic Acids 833 18-9 Synthesis of Ketones and Aldehydes from Nitriles 833... 

Functional modifiers are used in binary nomenclature to name anhydrides, e.g. acetic anhydride for (CH3-C0)20, and derivatives of ketones and aldehydes such as oximes, hydrazones and semicarbazones, e.g. acetone oxime for (CH3)2C=NOH. 

This chapter will revisit the lUPAC nomenclature system for aldehydes, ketones, and carboxylic acids, as well as introduce nomenclature for the four main acid derivatives acid chlorides, anhydrides, esters, and amides. The chapter will show the similarity of a carbonyl and an alkene in that both react with a Br0nsted-Lowry acid or a Lewis acid. The reaction of a carbonyl compound with an acid will generate a resonance stabilized oxocarbenium ion. Ketones and aldehydes react with nucleophiles by what is known as acyl addition to give an alkoxide product, which is converted to an alcohol in a second chemical step. Acid derivatives differ from aldehydes or ketones in that a leaving group is attached to the carbonyl carbon. Acid derivatives react with nucleophiles by what is known as acyl substitution, via a tetrahedral intermediate. 

The carbonyl group in glucose and ribose is an aldehyde such compounds are termed aldoses. Fructose, by contrast, has a ketone group and is therefore classified as a ketose. Glucose could also be termed an aldohexose and fructose a ketohexose, whereas ribose would be an aldopentose, names which indicate both the number of carbons and the nature of the carbonyl group. Another aspeet of nomenclature is the use of the suffix -ulose to indicate a ketose. Fructose could thus be referred to as a hexulose, though we are more likely to see this suffix in the names of specific sugars, e.g. ribulose is a ketose isomer of the aldose ribose. 

The structure and 2-ethyl-4-methylpentanal nomenclature of some aldehydes and ketones. 

The carbonyl group, C=0, is present in both aldehydes (RCH=0) and ketones (R2C=0). The IUPAC ending for naming aldehydes is -a/, and numbering begins with the carbonyl carbon. The ending for the names of ketones is -one, and the longest chain is numbered as usual. Common names are also widely used. Nomenclature is outlined in Sec. 9.1. 

A word about nomenclature. Once upon a time, chemists made a useful distinction between acetals (derived from aldehydes) and ketals (derived from ketones) which has since perished. The International Union of Pure and Applied Chemistry (IUPAC) decided (Rule C-331.1) that the term ketal is redundant and that the term acetal should now apply to all 1,1-to-ethers whether derived from aldehydes or ketones. Nevertheless, in A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993 (R. Panico, W.H. Powel, I-C Richter, Eds. Blackwell Science Oxford, 1993) the IUPAC graciously reinstated the term ketal , by popular demand, as a subclass of the generic term acetals (Rule R-5.6,4),... 

In Chapter 21 we continue the study of carbonyl compounds with a detailed look at aldehydes and ketones. We will first learn about the nomenclature, physical properties, and spectroscopic absorptions that characterize aldehydes and ketones. The remainder of Chapter 21 is devoted to nucleophilic addition reactions. Although we have already learned two examples of this reaction in Chapter 20, nucleophilic addition to aldehydes and ketones is a general reaction that occurs with many nucleophiles, forming a wide variety of products. 

Nomenclature of Aldehydes and Ketones.—The aldehydes are usually named from the acids into which they pass on oxidation, thus CH3.CHO is acetic aldehyde or acetaldehyde, as it is converted by oxidizing agents into acetic acid. In another system of nomenclature the name of an aldehyde is formed by adding the syllable al to the name of the hydrocarbon which contains the same number of carbon atoms as the aldehyde. According to this system acetaldehyde is called ethanal. 

An apparently similar reaction to the Arndt-Eistert process is the homologization of aldehydes and ketones by diazomethane. In the lUPAC nomenclature of transformations (1989 c), both are methylene insertions, but the homologization of aldehydes and ketones does not involve a carbene or ketene intermediate. We discussed it therefore in Section 7.7 in the context of dediazoniations via diazonium ions and carbocations. It is worthwhile to draw attention to the early work of Wolff, as mentioned at the beginning of this section. He discussed in one of his early papers the striking fact that, in boiling water, diazoacetophenone yields the expected (at least at that time) product of a hydroxy-de-diazoniation, but, in the presence of silver... 

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