# Why is this name not correct? "7-ethyl-3,4,4,7-tetramethylheptane"; what should it be?

Oct 3, 2017

$\text{3,4,4,7-tetramethylnonane}$

The longest chain is $9$ carbons, not $7$. So the parent name should be a nonane.

• Counting from the left, we then land on a methyl ($- {\text{CH}}_{3}$) group on carbon-3, two methyl groups on carbon-4, and one methyl group on carbon-7.

• Counting from the right, we then land on a methyl ($- {\text{CH}}_{3}$) group on carbon-3, two methyl groups on carbon-6, and one methyl group on carbon-7.

Part of the IUPAC naming is to minimize the carbon indexing, so counting from the left gives the correct carbon indexing. The last things we need to consider are

• how to denote duplicates
• how to denote how many duplicates of methyl groups we have.

Well...

• They are all methyl groups, so we don't have to worry about alphabetical ordering. We then list the carbon indices that the methyl groups are connected to.
• The prefix for four duplicate groups is "tetra".

So we should then get:

$\textcolor{b l u e}{\underline{\text{3,4,4,7-tetramethylnonane}}}$