Question

The following IUPAC name is incorrect. Explain why it is incorrect and give the correct IUPAC name. 2,2−dimethyl−4−ethylheptane

Answer 1

Answer:

Choice a. The compound name is alphabetized incorrectly.

The correct IUPAC name of this compound should be:

4-ethyl-2,2-dimethylheptane.

Explanation:

Draw the carbon backbone structure for "2,2-dimethyl-4-ethylheptane":

$\begin{array}{ccccccccccccc}& &\text{C}\\& & |\\\text{C}&-&\text{C}&-&\text{C}&-&\text{C}&-&\text{C}&-&\text{C}&-&\text{C}\\&&|&&&&|\\&&\text{C}&&&&\text{C}\\&&&&&&|\\&&&&&&\text{C} \end{array}$.

The seven-carbon backbone is indeed the longest chain in this compound.

$\begin{array}{ccccccccccccc}& &\text{C}\\& & |\\\text{C}^1&-&\text{C}^2&-&\text{C}^3&-&\text{C}^4&-&\text{C}^5&-&\text{C}^6&-&\text{C}^7\\&&|&&&&|\\&&\text{C}&&&&\text{C}\\&&&&&&|\\&&&&&&\text{C} \end{array}$.

Numbering from the end with the two methyl groups indeed minimizes the number on each group. However, the alphabetical order of the groups is not correct. There are two kinds of substitute groups in this compound:

• Two methyl groups, and
• One ethyl group.

The name for them will be

• 2,2-dimethyl, and
• 4-ethyl.

Ignore the multiplier prefixes (di-, tri-, etc.) while alphabetizing.

The ethyl group shall be placed before the two methyl groups. The name of the compound shall be:

4-ethyl-2,2-dimethylheptane.

Answer 2

Answer:

It's a.

Explanation:

The substituents are not in alphabetical order.  The ethyl substituent should come before the dimethyl ( Note the prefix  'di' is ignored).

The correct name is 4-ethyl-2,2-dimethylheptane.