Be sure to answer all parts. The following IUPAC name is incorrect. Which of the following is the best explanation for why the name is incorrect? 3−butyl−2,2−dimethylhexane The longest chain was not chosen. The compound is spelled incorrectly. The compound is alphabetized incorrectly. The compound has incorrectly labeled substituents. Correct the name: 1−ethyl−1−tert−butylpentane 4−tert−butyloctane (1,1,1−trimethyl)−sec−butylpentane tert−butyloctane

Which of the following is the best explanation for why the name is incorrect?

- The longest chain was not chosen.

- 4−tert−butyloctane

Explanation:

Let's think in the condensed formula:

CH₃C(CH₃)₂CH((CH₂)₃CH₃)CH₂CH₂CH₃.

We see that in the second carbon, we have two methyls and in the third carbon a butyl group.

But the name is incorrect because the longest chain was not chosen.

For IUPAC rules we have to determine:

- The longest main chain.

- From two chains of equal length, we may choose the most branched chain.

- It must be numbered starting from the end that has the closest branch.

- Each remainder is named as a substitute for the main chain

If we draw the alkane we have:

        CH₃

           |  

CH₃ - C  - - CH - - CH₂ -- CH₂ -- CH₃

          |         |

        CH₃   CH₂

                    |

                  CH₂

                    |

                  CH₂

                    |

                  CH₃

The carbon in black, is the first carbon, if we start to number from the underlined carbon, we would have the first branch at carbon 5. We have 8 carbons, so if we start to count from the black carbon (carbon 1), the branch will be at the carbon 4, that's the main chain.

So finally, at the carbon 4 we have a tertiary carbon (it is a single carbon which is joined with 3 others carbons, and the single carbon is it joined to the main chain). That is the tert-butyl group.

As it is in the fourth position, we can say that the alkane's name is 4−tert−butyloctane.

Notice that tert-butyl is a common name but it is available by IUPAC.