You will often come across labels on pharmaceuticals and in other contexts that are expressed in IUPAC names, and it is a part of your scientific training to be able to interpret them.

(a) Name the compound shown as (21) and

(b) Write the structural formula of 2-ethyl-1, 1-dimethylcyclohexane.

PLAN Use the procedure in Toolbox 11A.1. For part (b), interpret the name by identifying the root of the name and then attaching the substituents to the specified locations.

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Toolbox 11A.1 HOW TO NAME ALIPHATIC HYDROCARBONS CONCEPTUAL BASIS Because the types of carbon-carbon bonds present in a hydrocar- bon molecule typically dominate its properties, an aliphatic hydro- carbon is first classified as an alkane, alkene, or alkyne. Then the longest chain of carbon atoms is used to form the "root" of the name. Other hydrocarbon groups attached to the longest chain are named as side chains. PROCEDURE The following rules for naming hydrocarbons have been adopted by the International Union for Pure and Applied Chemistry (IUPAC). For additional information on naming hydrocarbons, see Section A in the IUPAC "Blue Book" (http://www.acdlabs.com/iupac/nomenclature). Alkanes Step 1 Count carbon atoms in the longest chain. The names of the first 12 straight-chain alkanes are given in Table 11A.1; they all end in -ane. Step 2 Identify and count substituents. Name a hydrocarbon side chain as a substituent by changing the ending -ane to-yl (as in the last two columns in Table 11A.1). Example: CH3CH- is the ethyl group.