Question 3.14: Naming Organic Compounds Name these compounds. (a) CH3CH2CH2...
Naming Organic Compounds
Name these compounds.
(a) CH_{3}CH_{2}CH_{2}CH_{2}CH_{3} (b) CH_{3}CHFCH_{2}CH_{3}
(c) CH_{3}CH_{2}CO_{2}H (d) CH_{3}CH_{2}CH(OH)CH_{2}CH_{3}
Analyze
First, determine the type of compound. Then, count the number of carbon atoms and select the appropriate stem (or prefix) from Table 3.7 to form the name. If the compound is an alcohol, change the final –e in the name to –ol; if it is a carboxylic acid, change the final –e to –oic acid.
| TABLE 3.7 Word Stem (or Prefix) Indicating the Number of Carbon Atoms in Simple Organic Molecules | |
| Stem (or prefix) | Number of C Atoms |
| Meth- | 1 |
| Eth- | 2 |
| Prop- | 3 |
| But- | 4 |
| Pent- | 5 |
| Hex- | 6 |
| Hept- | 7 |
| Oct- | 8 |
| Non- | 9 |
| Dec- | 10 |
(a) The structure is that of an alkane molecule with a five-carbon chain, so the compound is pentane.
(b) The structure is that of a fluoroalkane molecule with the F atom on the second C atom of a four-carbon chain. The compound is called 2-fluorobutane.
(c) The carbon chain in this structure is three C atoms long, with the end C atom in a carboxyl group. The compound is propanoic acid.
(d) This structure is that of an alcohol with the hydroxyl group on the third C atom of a five-carbon chain. The compound is called 3-pentanol.
Assess
In naming the compound in part (b), we stated that the F atom was bonded to the second C atom in a fourcarbon chain. There is some ambiguity in that statement because, as illustrated below, we can number the C atoms in two different ways.
\begin{array}{r c} \begin{matrix}\ \ \ \ \ \ \underset{|}{H} \ \ \ \ \ \underset{|}{F} \ \ \ \ \underset{|}{H} \ \ \ \ \ \underset{|}{H} \ \ \ \ \ \\ H-C-C-C-C-H\\ \ \ \ \ \ \ \overset{1|}{H} \ \ \ \ \overset{2|}{H} \ \ \ \ \overset{3|}{H} \ \ \ \ \overset{4|}{H} \ \ \ \ \ \ \ \ \\ \\ \text{2-fluorobutane (correct)}\end{matrix} \end{array}
\begin{array}{r c} \begin{matrix}\ \ \ \ \ \ \underset{|}{H} \ \ \ \ \ \underset{|}{F} \ \ \ \ \underset{|}{H} \ \ \ \ \ \underset{|}{H} \ \ \ \ \ \\ H-C-C-C-C-H\\ \ \ \ \ \ \ \overset{4|}{H} \ \ \ \ \ \overset{3|}{H} \ \ \ \ \overset{2|}{H} \ \ \ \ \overset{1|}{H} \ \ \ \ \ \ \ \\ \\ \text{3-fluorobutane (incorrect)}\end{matrix} \end{array}
By convention, we always number the carbon atoms so that the position of the functional group is designated by the smallest possible number. Thus, 2-fluorobutane is the correct name.