Naming compounds carboxylic acids

Notice that compounds 4 and 5 are named as hydroxy derivatives of carboxylic acids, rather than as carboxyl derivatives of alcohols. We have seen earlier that hydroxyl groups take precedence over double bonds, and double bonds take precedence over halogens and alkyl groups, in naming compounds. Carboxylic acids outrank all the common groups we have encountered to this point. 

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... 

The main classes of hydroxy compounds are aliphatic alcohols with OH groups attached to sp hybridized carbon atoms and phenols, in which the OH groups are attached to sp carbon atoms located in the aromatic systems. Another group of hydroxy compoimds—namely, the carboxylic acids, having the strucmral fragment COOH is discussed separately. 

In lUPAC names, the carboxylic acid group takes precedence over amino groups. Therefore, C-1 is the carboxyl group, the parent compound is propanoic acid, and the name is therefore 3-aminopropanoic acid. Its common name is (i-alanine, which is a component of pantothenic acid (vitamin B5) and some naturally occurring peptides. 

The common method of naming aldehydes corresponds very closely to that of the related acids (see Carboxylic acids), in that the term aldehyde is added to the base name of the acid. For example, formaldehyde (qv) comes from formic acid, acetaldehyde (qv) from acetic acid, and butyraldehyde (qv) from butyric acid. If the compound contains more than two aldehyde groups, or is cycHc, the name is formed using carbaldehyde to indicate the functionaUty. The lUPAC system of aldehyde nomenclature drops the final e from the name of the parent acycHc hydrocarbon and adds al If two aldehyde functional groups are present, the suffix -dialis used. The prefix formjlis used with polyfunctional compounds. Examples of nomenclature types are shown in Table 1. 

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. 

Chemical Name 3-Pyridine carboxylic acid compounded with 3,7-dihydro-7-[2-hydroxy-3-[(2-hydroxymethyl)methylamino] propyl] -1,3-dimethyl-1 H-purlne-2,6-dlone(1 1)... 

Compounds containing the -C=N functional group are called nitriles and undergo some chemistry similar to that of carboxylic acids. Simple open-chain nitriles are named by adding -nitrile as a suffix to the alkane name, with the nitrile carbon numbered Cl. 

As further examples, compounds 10 and 11 are both keto acids and mus be named as acids, but the parent name in 10 is that of a ring system (cyclo hexanecarboxylic acid) and the parent name in 11 is that of an open chair (propanoic acid). The full names are frrt/ s-2-(3-oxopropyl)cyclohexane carboxylic acid (10) and 3-(2-oxocyclohexyl)propanoic acid (11). 

The names of organic compounds are based on the names of the parent hydrocarbons alcohols contain —OH groups, carboxylic acids contain —COOH groups, and haloalkanes contain halogen atoms. 

There are actually three reactions called by the name Schmidt reaction, involving the addition of hydrazoic acid to carboxylic acids, aldehydes and ketones, and alcohols and alkenes. The most common is the reaction with carboxylic acids, illustrated above.Sulfuric acid is the most common catalyst, but Lewis acids have also been used. Good results are obtained for aliphatic R, especially for long chains. When R is aryl, the yields are variable, being best for sterically hindered compounds like mesi-toic acid. This method has the advantage over 18-13 and 18-14 that it is just one laboratory step from the acid to the amine, but conditions are more drastic. Under the acid conditions employed, the isocyanate is virtually never isolated. 

The second compound above raises an important issue how do you name the functional group when you have two functional groups in a compound One will go in the suffix of the name and the other will be a prefix in the substituent part of the name. But how do we choose which one goes as the suffix of the name There is a hierarchy that needs to be followed. The six groups shown above are listed according to their hierarchy, so a carboxylic acid takes precedence over an alcohol. A compound with both of these groups is named as a ketone and we put the term hydroxy in the substituent part of the name. 

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