Question 21.2: Naming Alkanes Name this alkane: CH3−CH2−CH2∣CH2∣CH–...
Naming Alkanes
Name this alkane:
CH _3- CH _2- \underset{\underset{CH _3}{\underset{\underset{|}{CH _2} }{|} } }{CH} – CH _2- CH _3| Naming Alkanes | |
| 1. Count the number of carbon atoms in the longest continuous carbon chain to determine the base name of the compound. Locate the prefix corresponding to this number of atoms in Table 21.5 and add the ending -ane to form the base name. | This compound has five carbon atoms in its longest continuous chain.
\begin{matrix} CH_{3}-CH_{2}-{CH}- CH 2- CH _3 \\\overset{\Large{|}}{CH{3}}\\\overset{\Large{|}}{CH_{3}} \end{matrix}
The correct prefix from Table 21.5 is pent-. The base name is pentane. |
| 2. Consider every branch from the base chain to be a substituent. Name each substituent according to Table 21.6. | This compound has one substituent named ethyl.
\begin{matrix} CH_{3}-CH_{2}-{CH}- CH 2- CH _3 \\{ \overset{\Large{|}}{CH{3}}}\\\begin{array}{c}{\overset{{\Large{\quad\quad\quad\nearrow}}}{\text{ethyl}} \quad}\end{array}\overset{\Large{|\quad\quad\quad~\quad\quad}}{CH_{3}\quad\quad~\quad\quad\quad\quad\quad\quad}\end{matrix} |
| 3. Beginning with the end closest to the branching, number the base chain and assign a number to each substituent. (If two substituents occur at equal distances from each end, go to the next substituent to determine from which end to start numbering.) | Number the base chain as follows:
\begin{matrix} C\overset{1}{H}_{3}-C\overset{2}{H}_{2}-\overset{3}{CH}- C\overset{4}{H} 2- C\overset{5}{H} _3 \\\overset{\Large{|}}{CH{3}}\\\overset{\Large{|}}{CH_{3}} \end{matrix}
Assign the number 3 to the ethyl substituent. |
| 4. Write the name of the compound in the following format: (substituent number)- (substituent name) (base name). If there are two or more substituents, give each one a number and list them alphabetically with hyphens between words and numbers. | The name of the compound is:
3-ethylpentane |
| 5. If a compound has two or more identical substituents, indicate the number of identical substituents with the prefix di- (2), tri- (3), or tetra- (4) before the substituent’s name.
Separate the numbers indicating the positions of the substituents relative to each other with a comma. Do not take the prefxes into account when alphabetizing. |
Does not apply to this compound. |
Table 21.5
| prefixes for Base Names of Alkane Chains | |
| Number of Carbon Atoms | Prefix |
| 1 | meth- |
| 2 | eth- |
| 3 | prop- |
| 4 | but- |
| 5 | pent- |
| 6 | hex- |
| 7 | hept- |
| 8 | oct- |
| 9 | non- |
| 10 | dec |
Table 21.6
| Common Alkyl Groups | |||
| Condensed Structural Formula | Name | Condensed Structural Formula | Name |
| -CH_3 | Methyl | -\underset{\overset{|}{CH_3} }{C} HCH_3 | Isopropyl |
| -CH_2CH_3 | Ethyl | -CH_2\underset{\overset{|}{CH_3} }{C} HCH_3 | Isobutyl |
| -CH_2CH_2CH_3 | Propyl | -\underset{\overset{|}{CH_3} }{C} HCH_2CH_3 | sec-Butyl |
| -CH_2CH_2CH_2CH_3 | Butyl | -\underset{\overset{|}{CH_3} }{\overset{\overset{CH_3}{|} }{C} }CH_3 | tert-Butyl |
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