The Nomenclature of Carboxylic Acids

The nomenclature of carboxylic acids and their derivatives was discussed in Section 7-6. Many carboxylic acids have trivial names and often are referred to as fatty acids. This term applies best to the naturally occurring straight-chain saturated and unsaturated aliphatic acids, which, as esters, are constituents of the fats, waxes, and oils of plants and animals. The most abundant of these fatty acids are palmitic, stearic, oleic, and linoleic acids. 

Table 22.2 summarizes the most important points about the nomenclature of carboxylic acid derivatives. 

A carboxylic acid with two COOH units is known as a dicarboxylic acid, or dioic acid. The molecule H02C-(CH2)3-C02H, for example, is named 1,5-pentanedioic acid. These compounds and more about the nomenclature of carboxylic acids are presented in Chapter 16 (Section 16.4). 

THE NOMENCLATURE OF CARBOXYLIC ACIDS AND CARBOXYLIC ACID DERIVATIVES... 

The Nomenclature of Carboxylic Acids and Carboxylic Acid Derivatives 723... 

Nomenclature of Carboxylic Acid Salts Salts of carboxylic acids are named simply by naming the cation, then naming the carboxylate ion by replacing the -ic acid part of the acid name with -ate. The preceding example shows that sodium hydroxide reacts with acetic acid to form sodium acetate. The following examples show the formation and nomenclature of some other salts ... 

The nomenclature of these acids is rather complicated. There are at least five systems in use. Here are some of the above in the different systems. The delta system numbers the double bonds from the carboxyl group (the A carbon), whereas the omega system indicates where the first double bond is counting from the other end of the molecule (the (o carbon). 

Seeing the Structure and Nomenclature of Carboxylic Acids and Derivatives... 

The nomenclature for carboxylic acids follows the familiar pattern of adding the functional group name -oic acid to the named hydrocarbon chain except that the common names formic acid and acetic acid are still widely accepted. Thus, formic acid is methanoic acid, acetic acid is ethanoic acid, propionic acid is propanoic acid, and -butyric acid is butanoic acid. The CAS numbers (Chemical Abstract Service, American Chemical Society) for the carboxylic acids are listed in Table 6.1 along with the physical properties. The CAS numbers refer to the major carboxylic acid component. Refer to the Material Safety Data Sheet (MSDS) for CAS numbers of any minor impurities in the solvent. 

Interestingly, the salts of carboxylic acids, utilize the same nomenclature system. Thus, conversion of ethanoic acid (acetic acid, CH3CO2H) to its sodium salt (with, e.g., aqueous sodium hydroxide, NaOH) produces water and sodium ethanoate (sodium acetate, CHsCOi Na" ). Furthermore, when the (RCO2-) group must be named as a substituent, it is called the acyloxy or R-carbonyloxy group. 

NOMENCLATURE OF CARBOXYLIC ACID DERIVATIVES The Acyl Group and Acid Derivatives... 

In this chapter, we will be discussing the chemistry of carboxylic acids, esters, acyl halides, anhydrides, and amides. This is dominated by substitution, where one group is exchanged with another. Substitution is NOT possible for aldehydes and ketones, as you can t displace H or — they are hopeless leaving groups. First, let s review some nomenclature. The suffix for carboxylic acids is -oic acid and the carbonyl of the acid is always numbered as C-1. The acid takes precedence over most other functional groups. Some examples are shown in Figure 15.1. Notice that when we have both a ketone and an acid in the molecule, it is named as a carboxylic acid, and the ketone is described as oxo. ... 

It IS hard to find a class of compounds in which the common names of its members have influenced organic nomenclature more than carboxylic acids Not only are the common names of carboxylic acids themselves abundant and widely used but the names of many other compounds are derived from them Benzene took its name from benzoic acid and propane from propionic acid not the other way around The name butane comes from butyric acid present m rancid butter The common names of most aldehydes are derived from the common names of carboxylic acids—valeraldehyde from valeric acid for exam pie Many carboxylic acids are better known by common names than by their systematic ones and the framers of the lUPAC rules have taken a liberal view toward accepting these common names as permissible alternatives to the systematic ones Table 19 1 lists both common and systematic names for a number of important carboxylic acids... 

This chapter concerns the preparation and reactions of acyl chlorides acid anhydrides thioesters esters amides and nitriles These com pounds are generally classified as carboxylic acid derivatives and their nomenclature is based on that of carboxylic acids... 

The nomenclature of penicillins requires special comment. Compound (2) can be named as follows (a) penicillin G (b) benzylpenicillin (note that the term penicillin may refer to the compound class (1), to the structural fragment (3) or, especially in the medical literature, to compound (2) itself) (c) 6/3-phenylacetamidopenicillanic acid (d) 2,2-dimethyl-6/3-phenylacetamidopenam-3a -carboxylic acid (e) (2S,5i ,6i )-3,3-di-methyl-7-oxo-6-(2-phenylacetamido)-4-thia-l-azabicyclo[3.2.0]heptane-2-carboxylic acid and (f) [2S-(2a,5a,6/3)]-3,3-dimethyl-7-oxo-6-[(phenylacetyl)amino]-4-thia-l-azabicyclo-[3.2.0]heptane-2-carboxylic acid. The numbered system shown in (2) is the one most commonly used in the penicillin literature and will be used in this chapter note that different number is used when (2) is named according to (e) and (f) above. 

Carboxylic acids and their derivatives are also an important part of Organic 11. We spend quite a few pages looking at the structure, nomenclature, synthesis, reactions, and spectroscopy of carboxylic acids. While on this topic in Chapter 12, we use a lot of acid-base chemistry, most of which you were exposed to in your introductory chemistry course. (For a quick review, look over a copy of Chemistry For Dummies or Chemistry Essentials For Dummies, both written by John T. Moore and published by Wiley.)... 

The nomenclature for this homologous series is somewhat confused. The term PANs has been used historically to denote peroxyacyl nitrates, and this terminology continues to be used extensively in the literature, despite the lack of adherence to traditional IUPAC rules of nomenclature. Because the PANs can be considered to be mixed anhydrides of carboxylic acids and nitric acid, another suggestion (Roberts, 1990) has been peroxyacetic nitric anhydride for CH,C(0)00NO2 and peroxy carboxylic nitric anhydrides for the whole class of compounds. Although it does not follow the IUPAC rules, it would be consistent with the widespread use of the name PAN but also reflect the structure more accurately. Table 6.20 shows the structures and commonly used names of some PANs that have been observed in the atmosphere and/or in laboratory studies. 

The IUPAC nomenclature for carboxylic acids uses the name of the alkane that corresponds to the longest continuous chain of carbon atoms. The final -e in the alkane name is replaced by the suffix -ok acid. The chain is numbered, starting with the carboxyl... 

The Greek symbols indicate the nomenclature of the carbon chains in certain amino acids. The carbon atom carrying (i.e.. next to) the carboxyl group is labeled a. 

Tire systematic lUPAC nomenclature for carboxylic acids requires the longest carbon chain of the molecule to be identified and the -e of alkane name to be replaced with -oic acid. 

The systematic approach for naming dicarboxylic acids (alkanes with carboxylic acids on either end) is the same as for carboxylic acids, except that the suffix is -dioic acid. Common name Nomenclature of dicarboxylic acids is aided by the acronym OMSGAP (Om s Gap), where each letter stands for the first letter of the first seven names for each dicarboxylic acid, starting from the simplest. 

The systematic lUPAC nomenclature for carboxylic acid derivatives is different for the various compounds which are in this vast category, but each is based upon the name of the carboxylic acid closest to the derivative in structure. Each type is discussed individually below. 

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