Question

Draw a structural formula for each of the following compounds. a. 2,2 -dimethylhexane b. 2,3-dimethylhexane c. 3,3-dimethylhexane d. 3,4-dimethylhexane e. 2,4 -dimethylhexane

Short answer

a. CH3-CH(CH3)-C(CH3)-CH2-CH2-CH2-CH3 b. CH3-CH(CH3)-CH(CH3)-CH2-CH2-CH3 c. CH3-CH2-C(CH3)2-CH2-CH2-CH3 d. CH3-CH2-CH(CH3)-CH(CH3)-CH2-CH3 e. CH3-CH(CH3)-CH(CH3)-CH2-CH3

Step-by-step solution

a. 2,2-dimethylhexane

First, draw the hexane chain, which has six carbon atoms in a straight chain. Next, add two methyl groups at the second carbon atom (from the number 2,2 in the name). It should look like this: CH3 | CH3-CH-C-CH2-CH2-CH2-CH3 | CH3

b. 2,3-dimethylhexane

Draw the hexane chain, which has six carbon atoms in a straight chain. Now, add one methyl group at the second carbon atom and another at the third carbon atom (from the number 2,3 in the name). The structural formula is: CH3 | CH3-CH-C-CH-CH2-CH2-CH3 | CH3

c. 3,3-dimethylhexane

Draw the hexane chain, which has six carbon atoms in a straight chain. Add two methyl groups at the third carbon atom (from the number 3,3 in the name). The structural formula looks like this: CH3-CH2-C(CH3)2-CH2-CH2-CH3

d. 3,4-dimethylhexane

Draw the hexane chain, which has six carbon atoms in a straight chain. Add one methyl group at the third carbon atom and another at the fourth carbon atom (from the number 3,4 in the name). The structural formula is: CH3-CH2-CH(CH3)-CH(CH3)-CH2-CH3

e. 2,4-dimethylhexane

Draw the hexane chain, which has six carbon atoms in a straight chain. Add one methyl group at the second carbon atom and another at the fourth carbon atom (from the number 2,4 in the name). The structural formula is: CH3 | CH3-CH-C-CH-CH2-CH3 | CH3

Key concepts

Structural Formula

In organic chemistry, the structural formula is a representation of the molecular structure that shows how atoms are arranged in a compound. Unlike simple chemical formulas that only specify the types and numbers of atoms in a molecule, the structural formula provides insight into the physical arrangement of these atoms. This is essential for understanding the properties and reacitivity of the molecule.
To write a structural formula, you must indicate every atom and bond explicitly. For a hexane molecule with dimethyl groups attached, this means drawing carbon atoms (as C) connected by single lines (which represent single covalent bonds) and showing the placement of hydrogen atoms as needed.

• This detailed depiction lets us visualize not only which atoms are present but also how they interact.
• Such formulas can show the branching of molecules, which is critical in illustrating isomers like the dimethylhexanes described in the problem.
• For complex hydrocarbons, structural formulas help identify various functional groups and substituents, such as methyl groups, attached to the main carbon chain.

Alkanes

Alkanes are a family of hydrocarbons consisting only of carbon and hydrogen atoms connected by single bonds. They are saturated compounds, meaning that they carry the maximum number of hydrogen atoms possible for their carbon structure.
In the context of the exercise, the term "hexane" refers to an alkane with six carbon atoms. This gives us the base structure for the molecules in the problem. The general formula for alkanes is \(C_nH_{2n+2}\), where \(n\) is the number of carbon atoms.

• Alkanes are known for being relatively nonreactive due to their strong C-H and C-C single bonds.
• They serve as a basic scaffold to which more reactive functional groups can be attached.
• In practice, recognizing the longer alkane chains helps in understanding where additional groups, like methyl groups, will attach.

Methyl Groups

Methyl groups are small hydrocarbon branches with the formula \(CH_3\). They are derived from methane and often serve as substituents on larger hydrocarbons. When attached to a carbon chain, they modify the chemical and physical properties of the molecule.
In the problem presented, methyl groups are found attached to different positions on the hexane chain. For instance, in 2,2-dimethylhexane, two methyl groups attach at the second carbon in the chain.

• The presence of one or more methyl groups influences the shape and therefore the reactivity of a molecule.
• These groups are shown as branches off the main carbon chain in the structural formulae.
• Correctly identifying the position of methyl groups is critical to distinguishing different isomers, such as 2,3-dimethylhexane and 3,3-dimethylhexane.

Hexane Chain

The hexane chain is the core structure for the compounds under review in the exercise. Hexane is an alkane composed of six carbon atoms arranged in a linear sequence.
It provides the backbone upon which additional groups, like methyl groups, can be added, creating branched alkanes. Visualizing the chain involves identifying each carbon atom and noting its adjacent hydrogen atoms to reach a saturated state with no pi bonds.

• Understanding the linear structure is essential before adding branches or substituents.
• Numbering the carbons starting from one end helps determine where to attach different groups, like those on the second or third carbon.
• The hexane chain provides stability and scaffold for more complex configurations in organic chemistry.