Answer:
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.
