Nomenclature of Carbonyl Compounds

In a generic carbonyl compound R2C=0, there is a vast array of possible substitution patterns, and there is a separate name for each one of them. Simple compounds in which both R groups are hydrocarbons such as alkyl, alkenyl, or aryl are called ketones. If one R group is hydrogen, the compound is an aldehyde, and the molecule in which both R groups are hydrogen is called formaldehyde. 

FIGURE 16.7 A few aldehydes and their lUPAC names are shown. Common names are given in parentheses. 

Compounds containing two aldehydes are dials. In this case, the final e of the parent name is not dropped before adding dial (Fig. 16.8). 

Ketones, too, have common names, but most have been discarded. An exception is the name for the simplest member of the class, dimethyl ketone, which is still called acetone. Ketones are named in several ways. For example, acetone is also known as 

FIGURE 16.9 Simple ketones can be named in many ways. The lUPAC names are listed first. 

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Nomenclature of carbonyl compounds presents a bit of a problem in that several alternative names may be possible for almost any compound. 

Figure 9-1 shows the carbonyl group. Note This name isn t part of the formal nomenclature of organic compounds, but just a simple name for a commonly seen group. 

In Chapter 9 you see how to identify the different types of compounds containing the carbonyl group. Now you take a look at the naming (nomenclature) of these compounds. 

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. 

Comment. The reality of the Pt-Pt linkage is still in doubt but this pattern of nomenclature may have applications in another connection (see treatment of carbonyl compounds later). 

Chapter 15 provides a brief introduction to commonly used organic molecules that also have a carbon-metal bond—organometallics. Chapter 16 introduces the fundamental characteristics of molecules that contain the carbon functional group, along with a review of the nomenclature of carbonyl-containing molecules. Carbonyl compounds are often prepared by oxidation reactions, and several key oxidation reactions are discussed in Chapter 17. Oxidation reactions of a few other functional groups are included. Chapter 18 elaborates the chemical reactions of the carbonyl-containing molecules known as aldehydes and ketones. This chemistry is dominated by the acyl addition reaction introduced in Chapter 16. 

Aldehydes are the class of carbonyl compounds where one substituent is an alkyl, alkenyl, or aryl group, and the other is a hydrogen atom, 4.34. The suffix for aldehydes is -al added to the hydrocarbon skeleton name, so if R = CH3, 4.34 would be ethanal (the old name, which is still commonly used, was acetaldehyde). In formal nomenclature, the aldehyde carbon is designated as C-1. When R = H, the name is methanal, but this compound is almost invariably known by its common name, formaldehyde. With more complex structures, the longest chain starting at C-1 is discerned, numbered, and the substituents put in as usual. So 4.35 is 2,3-dimethylpentanal. 

Structure and Classification of Alcohols 425 10-3 Nomenclature of Alcohols and Phenols 427 10-4 Physical Properties of Alcohols 430 10-5 Commercially Important Alcohols 433 10-6 Acidity of Alcohols and Phenols 435 10-7 Synthesis of Alcohols Introduction and Review 438 Summary Previous Alcohol Syntheses 438 10-8 Organometallic Reagents for Alcohol Synthesis 440 10-9 Addition of Organometallic Reagents to Carbonyl Compounds 443... 

Table 19.1 lists common parent names for some simple carboxyhc acids. These parent names are used in the nomenclature of many other compounds with carbonyl groups (Chapters 21 and 22). 

In Section 8.1, we saw that a carbonyl group has a higher nomenclature priority than an alcohol or an amine group. However, all carbonyl compounds do not have the same priority. The nomenclature priorities of the various carbonyl groups are shown in Table 18.1. 

Several important classes of molecules have the carbonyl unit (-C=0) as a key part of their structure. They are generically known as carbonyl compounds. The chemistry associated with carbonyl compounds is important to many chemical reactions. The carbonyl unit is reactive because it is polarized and also contains a weak and reactive 7i-bond. This chapter is primarily dedicated to learning the identity, structure, and nomenclature of the key carbonyl-containing functional groups, as well as the most fundamental aspects of their chemical reactivity. These include aldehydes, ketones, carboxylic acids, and carboxylic acid derivatives. 

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. 

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