Question

Explain why each is an incorrect IUPAC name and write the correct IUPAC name for the intended compound. (a) 1,3 -Dimethylbutane (b) 4 -Methylpentane (c) 2,2 -Diethylbutane (d) 2-Ethyl-3-methylpentane (e) 2-Propylpentane (f) 2,2 -Diethylheptane (g) 2,2-Dimethylcyclopropane (h) 1 -Ethyl-5-methylcyclohexane

Short answer

Answer: 2-Ethyl-3-methylpentane

Step-by-step solution

Identify the error

In this case, the compound is named as if there are two methyl groups at positions 1 and 3 of a butane (4-carbon) chain. However, since the methyl groups are attached on the same side and not in the middle of the chain, the name is incorrect.

Correct IUPAC name

The correct structure has a pentane (5-carbon) chain with methyl groups at positions 2 and 3. Therefore, the correct IUPAC name is 2,3-Dimethylpentane. #b)# 4 -Methylpentane

Identify the error

In this case, the compound is named as if there is a methyl group at position 4 on a pentane (5-carbon) chain. However, this name is incorrect because the position of the methyl group is not the lowest possible.

Correct IUPAC name

The correct structure has the methyl group at position 2 on the pentane chain. Therefore, the correct IUPAC name is 2-Methylpentane. #c)# 2,2 -Diethylbutane

Identify the error

In this case, the compound is named as if there are two ethyl groups at position 2 of a butane (4-carbon) chain. However, this structure cannot exist because there is not enough space for two ethyl groups at the same position.

Correct IUPAC name

The correct structure should have an ethyl group at positions 2 and 3 of the butane chain. Therefore, the correct IUPAC name is 2,3-Diethylbutane. #d)# 2-Ethyl-3-methylpentane

Identify the error

In this case, the compound is named correctly according to IUPAC guidelines. There are no errors to identify.

Correct IUPAC name

The correct IUPAC name is 2-Ethyl-3-methylpentane. #e)# 2-Propylpentane

Identify the error

In this case, the compound is named as if there is a propyl group at position 2 of a pentane (5-carbon) chain. However, this structure is not correct, as the propyl group should be part of the main chain.

Correct IUPAC name

The correct structure has an octane (8-carbon) chain (5+3=8). Therefore, the correct IUPAC name is Octane. #f)# 2,2 -Diethylheptane

Identify the error

In this case, the compound is named as if there are two ethyl groups at position 2 of a heptane (7-carbon) chain. However, this name is incorrect because the position of the ethyl groups is not the lowest possible.

Correct IUPAC name

The correct structure should have the ethyl groups at positions 3 and 4. Therefore, the correct IUPAC name is 3,4-Diethylheptane. #g)# 2,2-Dimethylcyclopropane

Identify the error

In this case, the compound is named as if there are two methyl groups at position 2 of a cyclopropane ring. However, this structure cannot be named as a cyclopropane, as there is no carbon available at position 2 to attach two methyl groups.

Correct IUPAC name

The correct structure should be a cyclobutane, with a methyl group at positions 1 and 2. Therefore, the correct IUPAC name is 1,2-Dimethylcyclobutane. #h)# 1 -Ethyl-5-methylcyclohexane

Identify the error

In this case, the compound is named as if there is an ethyl group at position 1 and a methyl group at position 5 on a cyclohexane ring. However, this name is not the lowest possible for the numbering.

Correct IUPAC name

The correct structure should have the ethyl group at position 1 and the methyl group at position 2. Therefore, the correct IUPAC name is 1-Ethyl-2-methylcyclohexane.