Question

Draw the structural formula for each of the following.

a. 3-isobutylhexane

b. 2, 2, 4-trimethylpentane, also called isooctane. This substance is the reference (100level) for octane ratings.

c. 2-tert-butylpentaned.

d. The names given in parts a and c are incorrect. Give the correct names for these hydrocarbons.

Short answer

a.

b.

c.

d.

Correct name for part a is $4$-ethyl-$2$-methylheptane.

The correct name for part c is $2,2,3$-trimethylhexane.

Step-by-step solution

Define the structural isomers.

In structural isomers, atoms are organized in a different order but have the same molecular formula.

The structural isomers are isomers that differ in the atomic arrangement of molecules without any reference to the spatial arrangement.

Subpart (a)The structural formula for 3-isobutylhexane.

The longest continuous carbon chain has six carbon atoms, as indicated by the basic name hexane. This substance is an alkane, as indicated by the suffix-ane.

The 3-isobutyl prefix indicates that an isobutyl group is present at position 3.

The graphic below displays the 3-isobutylhexane structural formula.

The structure makes it very evident that this is not the proper name for this combination. There are 7 C-atoms in the longest continuous chain.

Here, position2has one methyl group, and position4has one ethyl group.

Thus, 4-ethyl-2-methylheptane is the proper name for this compound.

Subpart (b) Drawing structural formula for 2, 2, 4-trimethylpentane

The diagram below depicts the 2, 2, 4-trimethylpentane molecule's structure.

The longest continuous carbon chain has five carbon atoms, as indicated by the basic name pentane.

This substance is an alkane, as indicated by the prefix -ane.

Two methyl groups are present at position 2, and a third methyl group is present at position 4, according to the prefix 2, 2, 4-trimethyl.

Drawing structural formula for  2-tert-butylpentaned

The longest continuous carbon chain has five carbon atoms, as indicated by the basic name pentane.

This substance is an alkane, as indicated by the prefix -ane.

The tert-butyl group is present at position2according to the prefix2-tert-butyl.

The structure below makes it very evident that this is not the proper name for this combination. There are six carbon atoms in the longest continuous chain. Two methyl groups are present at position 2, and one methyl group is present at position 3.

Thus, 2, 2, 3-trimethylhexane is the proper name for the substance.

Subpart (d) Determining correct names for parts a and c.

The hydrocarbon in 9a, 3-isobutylhexane, does not have the correct name since, when referring to the structure, the longest Carbon chain that may be generated from the structure should be called the parent chain.

Observe that in this instance, a 7 Carbon-Carbon chain can be formed in place of the typical 6 Carbon-Carbon chain to create an even longer chain. Therefore, heptane rather than hexane should be the parent chain.

Following that, take note of the methyl group linked to the third carbon and the ethyl group attached to the fourth carbon. The hydrocarbon's correct name should thus be 4-ethyl-2-methylheptane.

Since the name of the parent chain should correspond to the longest carbon chain that might be generated from the structure, the hydrocarbon in 9c(2-tert-butylpentane) has the wrong name.

Observe that in this instance, a 6 Carbon-Carbon chain can be formed in place of the 5 Carbon-Carbon chain to create an even longer chain. Hexane, not pentane, should therefore make up the parent chain.

Next, take note of the methyl groups that are connected to various carbons. The third carbon has one methyl group attached, and the second carbon has two methyl groups. Thus, 2, 2, 3-trimethylhexane should be used as the proper name for the hydrocarbon.