An Introduction to Nomenclature

Problem 4.9 Draw the five constitutional isomers that have molecular formula C5H10 and contain one ring. 

How are organic compounds named Long ago, the name of a compound was often based on the plant or animal source from which it was obtained. For example, the name for formic acid, a caustic compound isolated from certain ants, comes from the Latin word formica, meaning ant and alli-cin, the pungent principle of garlic, is derived from the botanical name for garlic. Allium sativum. Other compounds were named by their discoverer for more personal reasons. Adolf von Baeyer supposedly named barbituric acid after a woman named Barbara, although speculation continues on Barbara s identity—a lover, a Munich waitress, or even St. Barbara. 

Garlic has been a valued commodity throughout history. It has been used In Chinese herbal medicine for more than 4000 years, as a form of currency In Siberia, and as a repellent for witches by the Saxons. Today It Is used as a dietary supplement because of Its reported health benefits. Allicin, the molecule responsible for garlic s odor. Is a rather unstable molecule that Is not stored In the garlic bulb, but rather Is produced by the action of enzymes when the bulb Is crushed or bruised. 

With the isolation and preparation of thousands of new organic compounds it became clear that each organic compound must have an unambiguous name, derived from a set of easily remembered rules. A systematic method of naming compounds was developed by the /ntemational f/nion of Pure and Applied Chemistry. It is referred to as the lUPAC system of nomenclature how it can be used to name alkanes is explained in Sections 4.4 and 4.5. 

The lUPAC system of nomenclature has been regularly revised since it was first adopted in 1892. Revisions in 1979 and 1993 and recent extensive reconunendations in 2004 have given chemists a v a tt A i)pes % y changes are minor. For example, the 1979 

Draw the five constitutional isomers having molecular formula C6H14. 

Draw all constitutional isomers having molecular formula CgHie that contain seven carbons in the longest chain and a single CH3 group bonded to the chain. 

Draw the structure of an alkane with molecular formula C7Hig that (a) contains one 4° carbon  

Cycloalkanes have molecular formula C H2 and contain carbon atoms arranged in a ring. 

Think of a cycloalkane as being formed by removing two H atoms from the end carbons of a chain, and then bonding the two carbons together. Simple cycloalkanes are named by adding the prefix cyclo- to the name of the acyclic alkane having the same number of carbons. 

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