Question

Chloropropane is derived from propane by substituting Cl for \(\mathrm{H}\) on one of the carbon atoms. (a) Draw the structural formulas for the two isomers of chloropropane. (b) Suggest names for these two compounds.

Short answer

The two isomers of chloropropane are: 1. \( \mathrm{CH_2ClCH_2CH_3} \) - 1-chloropropane 2. \( \mathrm{CH_3CHClCH_3} \) - 2-chloropropane

Step-by-step solution

Understand Isomers and Compounds

An isomer is a compound with the same molecular formula but different structural arrangements of the atoms in the molecule. In other words, they have the same number and type of atoms, but their arrangement in space is different. A compound is a substance made up of two or more elements that are chemically bonded together, like chloropropane. In this problem, we have to derive chloropropane from propane by substituting a chlorine (Cl) atom for a hydrogen (H) atom on one of the carbon atoms.

Draw the Structural Formulas of the Two Isomers of Chloropropane

First, let's look at the structural formula of propane: Propane: \( \mathrm{CH_3CH_2CH_3} \) Now, to create the two isomers of chloropropane, we will substitute one hydrogen atom on either the first or second carbon atom (as there are only two types of carbon atoms in propane, terminal and central) with a chlorine atom. The resulting isomers are: 1. When Cl is attached to the first carbon atom: \( \mathrm{CH_2ClCH_2CH_3} \) 2. When Cl is attached to the second carbon atom: \( \mathrm{CH_3CHClCH_3} \)

Name the Two Isomers of Chloropropane

Now that we have the structural formulas of the two isomers of chloropropane, we can give them their respective names using the IUPAC (International Union of Pure and Applied Chemistry) naming system. 1. First isomer: \( \mathrm{CH_2ClCH_2CH_3} \) The Cl is attached to the first carbon atom, so the IUPAC name for this isomer is: 1-chloropropane 2. Second isomer: \( \mathrm{CH_3CHClCH_3} \) The Cl is attached to the second carbon atom, so the IUPAC name for this isomer is: 2-chloropropane In conclusion, the two isomers of chloropropane have the following structural formulas and names: 1. \( \mathrm{CH_2ClCH_2CH_3} \) - 1-chloropropane 2. \( \mathrm{CH_3CHClCH_3} \) - 2-chloropropane

Key concepts

Structural Formulas

Understanding the structural formulas of organic compounds is crucial for identifying different isomers. When it comes to chloropropane, we're dealing with a molecule formed by replacing one hydrogen atom in propane (\(\mathrm{CH_3CH_2CH_3}\)) with a chlorine (Cl) atom. Structurally, propane consists of a chain of three carbon atoms, with hydrogen atoms fulfilling the remaining needs for carbon's four bonds.
By substituting a hydrogen atom with a chlorine atom, two possible structural variations arise.

• The chlorine atom could replace a hydrogen atom bonded to the first carbon, resulting in the structural formula \(\mathrm{CH_2ClCH_2CH_3}\). Here, the chlorine is positioned on a terminal carbon.
• Alternatively, the chlorine could attach to the second carbon in the chain, producing \(\mathrm{CH_3CHClCH_3}\), where the chlorine is on the central carbon.

Each formula visually represents the connection between atoms in the molecule, offering insight into how different configurations can still maintain the same molecular formula.

IUPAC Naming

The IUPAC naming system provides a standardized way to name chemical compounds, which helps researchers and students communicate clearly. For chloropropane, applying the IUPAC rules ensures accurate and systematic identification.
First, identify the longest carbon chain, which is three carbons for both isomers in this example. Since both derivatives of propane involve a chlorine substituent, the position of this substituent determines its IUPAC name.

• For \(\mathrm{CH_2ClCH_2CH_3}\), the chlorine is on the first carbon atom. This leads to the name: **1-chloropropane**.
• For \(\mathrm{CH_3CHClCH_3}\), the chlorine is attached to the second carbon atom. Thus, this structure is named: **2-chloropropane**.

The numbering from the end nearest to the chlorine substituent ensures these names reflect the exact positions and conform to systematic chemical nomenclature norms.

Chemical Isomerism

Chemical isomerism occurs when compounds have the same molecular formula but differ in the arrangement of atoms. The two isomers of chloropropane exemplify **structural isomerism**, a common type of isomerism.
In structural isomerism, molecules have the same numbers and kinds of atoms but differ in connectivity.

• 1-chloropropane has the chlorine atom on the terminal carbon, creating one variant of chlorine placement.
• 2-chloropropane shifts the chlorine to the central carbon, offering a different structure with distinctive properties.

These differences in atom connectivity can lead to changes in the compound's properties, such as boiling points, melting points, and reactivity. This highlights the importance of understanding isomerism in both academic and practical chemical contexts.