Question

Chloropropane is derived from propane by substituting \(\mathrm{Cl}\) for 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 have the structural formulas: 1. 1-chloropropane: \(CH_2ClCH_2CH_3\) 2. 2-chloropropane: \(CH_3CHClCH_3\)

Step-by-step solution

Understand the structure of propane

Propane consists of three carbon atoms, connected by single covalent bonds, and each carbon atom is bonded to the remaining valence electrons with hydrogen atoms. The molecular formula is \(C_3H_8\). The structure can be represented as: \(CH_3CH_2CH_3\)

Replace one hydrogen atom with chlorine

In chloropropane, we need to replace one hydrogen atom in propane with a chlorine atom. There are two possible positions for that: 1. On an end (or terminal) carbon atom 2. On the middle carbon atom These substitutions will result in two different isomers.

Draw the isomers of chloropropane

Following the positions discussed in step 2, the two isomers will have the following structural formulas: 1. If we replace H of the terminal carbon atom (first C in the chain), we end up with the structure: \(CH_2ClCH_2CH_3\) 2. If we replace H of the middle carbon atom (second C in the chain), the structure will be: \(CH_3CHClCH_3\)

Suggest names for the isomers of chloropropane

We can now suggest names for these two compounds following the IUPAC nomenclature rules: 1. The first isomer has a chlorine atom on the first carbon, so the name is 1-chloropropane. 2. The second isomer has a chlorine atom on the second carbon, so the name is 2-chloropropane. The two isomers of chloropropane are: (a) 1-chloropropane with structure \(CH_2ClCH_2CH_3\) (b) 2-chloropropane with structure \(CH_3CHClCH_3\)

Key concepts

Propane Structure

Propane is a type of hydrocarbon with the molecular formula \(C_3H_8\). It belongs to the alkane group, which is characterized by single covalent bonds between carbon atoms. In the propane structure, three carbon atoms are linked in a straight chain, and they are completed by hydrogen atoms bonding to the remaining available valency of the carbon atoms. This gives propane its complete formula of \(CH_3CH_2CH_3\).
The structural representation can help visualize how the atoms are arranged. Each terminal (end) carbon atom in propane is bonded to three hydrogen atoms, while the middle carbon bonds with two hydrogen atoms. This structure is important as it sets the stage for chemical reactions such as forming different isomers when substituting atoms, like chlorine, onto the chain.

Covalent Bonds

In organic chemistry, covalent bonds are what hold molecules like propane together. These bonds occur when atoms share electrons to fill their outer shell, creating a stable molecule. Carbon atoms form four covalent bonds due to their four valence electrons.
In propane, each carbon atom is linked to others via single covalent bonds. This is typical of alkanes where only single bonds (\(\sigma\) bonds) link carbon atoms, making them saturated hydrocarbons. - Terminal carbon atoms in propane form three covalent bonds with hydrogen and one with another carbon.- The middle carbon atom forms two bonds with hydrogen and two with other carbon atoms.
Understanding covalent bonds is key to grasping how molecules like propane interact chemically and how substitutions, such as replacing hydrogen with chlorine, create new compounds.

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) provides a systematic way to name chemical compounds, making it easier to identify and communicate about them. When naming chloropropane isomers, we adhere to this nomenclature.
The position of the chlorine substituent in chloropropane determines the isomer’s name: - For the carbon chain, number from the end closest to the first substituent to give the lowest possible number. - When chlorine is attached to the first carbon, the compound is named 1-chloropropane. - For a chlorine atom on the second carbon, it is named 2-chloropropane.
IUPAC names not only help distinguish between different isomers like 1-chloropropane and 2-chloropropane, but ensure that the structure of the molecules is communicated effectively, supporting accurate scientific dialogue.