Question

Draw a structural formula for each of the following compounds. a. 2-methylpropane b. 2-methylbutane c. 2-methylpentane d. 2-methylhexane

Short answer

a. CH3 | CH3-C-CH3 b. CH3 CH3 | | CH3-C-CH2-C-CH3 c. CH3 CH3 | | CH3-C-CH2-C-CH2-C-CH3 d. CH3 CH3 | | CH3-C-CH2-C-CH2-CH2-C-CH3

Step-by-step solution

Identify the longest carbon chain

Using the names given, we can identify the main carbon chain in each compound by looking at their suffixes: propane, butane, pentane, and hexane. These contain 3, 4, 5, and 6 carbon atoms, respectively.

Identify the position of the methyl group

In each compound, the prefix "2-methyl" indicates that there is a methyl group (CH3-) attached to the second carbon atom in the main chain.

Draw the structural formula for each compound

Now, we will draw the structural formula for each compound using the information from steps 1 and 2. a. 2-methylpropane: Propane has a three-carbon chain, the structure is: CH3 | CH3-C-CH3 b. 2-methylbutane: Butane has a four-carbon chain. The structure is: CH3 CH3 | | CH3-C-CH2-C-CH3 c. 2-methylpentane: Pentane has a five-carbon chain. The structure is: CH3 CH3 | | CH3-C-CH2-C-CH2-C-CH3 d. 2-methylhexane: Hexane has a six-carbon chain. The structure is: CH3 CH3 | | CH3-C-CH2-C-CH2-CH2-C-CH3

Key concepts

Structural Formula

In Organic Chemistry, a structural formula is a way to represent molecules by showing how atoms are connected to each other through chemical bonds. Unlike simple molecular formulas, which only display the number and type of atoms, structural formulas give us a visual depiction of the molecule's geometry. This representation can be crucial when trying to understand the properties and behavior of a compound.
For example:

• The structural formula of ethanol is represented as CH₃CH₂OH. It clearly shows the arrangement of carbon, hydrogen, and oxygen atoms.
• Simple line representations might use dashes to show bonds, whereas more detailed ball-and-stick models give a three-dimensional view.
• Structural formulas help in visualizing branches in complex molecules like those in the exercise, where a methyl group (CH₃) is attached to a carbon chain.

Understanding structural formulas is vital for identifying how molecules might interact in reactions or biological processes.

Alkanes

Alkanes are a key class of hydrocarbons in organic chemistry. These compounds contain only carbon and hydrogen atoms. They are also known as saturated hydrocarbons because they have single bonds between carbon atoms. Alkanes can be straight chains or branched chains.
Here's a simple way to grasp the concept of alkanes:

• The general formula for an alkane is C_nH_2n+2, where n is the number of carbon atoms.
• In alkanes, each carbon atom forms four single covalent bonds with other atoms. Typically, this leads to a zig-zag or linear structure.
• Examples include methane (CH₄), ethane (C₂H₆), and propane (C₃H₈).

Alkanes are typically not very reactive due to their strong C-C and C-H bonds, but they play a significant role as fuels—for instance, propane is used in home heating. Identifying the parent alkane chain is crucial before further modification or branching, as shown in the exercises.

Methyl Groups

A methyl group is a chemical group derived from methane (CH₄) by the removal of one hydrogen atom, resulting in CH₃-. When a methyl group is connected to a carbon chain, it acts as a branch, changing the properties and name of the parent alkane. This is how branched alkanes form.
To understand the importance of methyl groups in organic chemistry, consider:

• Methyl groups are named as substituents in the IUPAC nomenclature when not part of the main carbon chain.
• They can be found attached to various positions on a carbon chain, significantly affecting the compound's structure and properties.
• In the case of the exercise examples, the methyl group is appended at the second carbon of the main chain.

Recognizing where and how methyl groups attach is essential for drawing structural formulas accurately. Their presence can alter boiling points, densities, and even the reactivity of compounds.