Isobutane nomenclature

Alkanes are a class of saturated hydrocarbons with the general formula C H2n. -2- They contain no functional groups, are relatively inert, and can be either straight-chain (normal) or branched. Alkanes are named by a series of IUPAC rules of nomenclature. Compounds that have the same chemical formula but different structures are called isomers. More specifically, compounds such as butane and isobutane, which differ in their connections between atoms, are called constitutional isomers. 

The general trend in substitutive nomenclature is to use fewer trivial or retained names and to approach substitutive nomenclature more systematically. A total of 209 trivial names are to be retained 81 for parent hydrides and 58 (those in Chapter 4, Section 4.5.7, p. 91) for functional parent hydrides. These are so well anchored in nomenclature that they will probably survive for a great many years. Finally, 70 trivial names, such as isobutane and neopentane, are still allowed to be specific for non-substituted compounds. Presumably some of these will be discarded during later revisions of the Nomenclature of Organic Chemistry. 

If all alkanes had unbranched (straight-chain) structures, their nomenclature would be simple. Most alkanes have structural isomers, however, and we need a way of naming all the different isomers. For example, there are two isomers of formula C4H10. The unbranched isomer is simply called butane (or n-butane, meaning normal butane), and the branched isomer is called isobutane, meaning an isomer of butane. ... 

Isobutane, isopentane, and neopentane are common names or trivial names, meaning historical names arising from common usage. Common names cannot easily describe the larger, more complicated molecules having many isomers, however. The number of isomers for any molecular formula grows rapidly as the number of carbon atoms increases. For example, there are 5 structural isomers of hexane, 18 isomers of octane, and 75 isomers of decane We need a system of nomenclature that enables us to name complicated molecules without having to memorize hundreds of these historical common names. 

In addition to the most modem systematic nomenclature system, several older nomenclature systems are still in use in organic chemistry. The simplest compounds are more often known by their older names than their most modem names, especially in commerce. For example, ethanol is often called ethyl alcohol or just alcohol, and methanol is called methyl alcohol. Even older names, grain alcohol and wood alcohol, respectively, are still used for these two compounds. Similarly, methanal is more generally called formaldehyde, methanoic acid is frequently referred to as formic acid, and methylpropane is often called isobutane. 

Nomenclature. The question arises as to how the various isomers of a hydrocarbon can be named and distinguished. When the number of poffiible isomers is small this offers no problem. The two isomers of butane are named normal butane and isobutane. The three isomers of pentane are known as normal pentane, isopentane, and neopentane. 

This method of nomenclature is called systematic nomenclature. It is also called lUPAC nomenclature because it was designed by a commission of the International Union of Pure and Applied Chemistry (abbreviated lUPAC and pronounced eye-you-pack ) at a meeting in Geneva, Switzerland, in 1892. The lUPAC mles have been continually revised by the commission since then. Names such as isobutane and neopentane—nonsystematic names—are called common names and are shown in red in this text. The systematic or lUPAC names are shown in blue. Before we can understand how a systematic name for an alkane is constructed, we must learn how to name alkyl substituents. 

The names for the two isomeric butanes (n-butane and isobutane) illustrate the important features of the common nomenclature system used for alkanes. The stem but-indicates that four carbons are present in the molecule. The -ane ending signifies the alkane family. The prefix n- indicates that all carbons form an unbranched chain. The prefix iso- refers to compounds in which all carbons except one are in a continuous chain and in which that one carbon is branched from a next-to-the-end carbon, as shown ... 

Isobutane is actually named with propane as the base name under the official naming rules adopted by the lUPAC, since the longest straight chain of carbons in isobutane is three. A detailed look at the lUPAC nomenclature... 

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