Question

Draw all the structural isomers of compounds with the formula \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Cl}_{2}\). Indicate which isomers are chiral, and give them systematic names.

Short answer

There are several isomers: 1,1-dichlorobutane, 1,2-dichlorobutane, 1,3-dichlorobutane, 1,4-dichlorobutane, 2,2-dichlorobutane, 2,3-dichlorobutane. The chiral ones are 1,2-dichlorobutane and 2,3-dichlorobutane.

Step-by-step solution

Define Structural Isomers

Structural isomers have the same molecular formula but different arrangements of atoms. For a compound with the formula \( \text{C}_4 \text{H}_8 \text{Cl}_2 \), we'll explore various ways to arrange the carbon atoms and attach two chlorine atoms.

Draw Linear Isomers

Start by drawing isomers with a straight chain of four carbon atoms: 1. Attach the two chlorine atoms on different carbon atoms. - 1,1-dichlorobutane - 1,2-dichlorobutane (two enantiomers, chiral) - 1,3-dichlorobutane - 1,4-dichlorobutane 2. Attach both chlorine atoms on the same carbon atom. - 2,2-dichlorobutane - 1,1-dichlorobutane (same as above, repositioned)

Draw Branched Isomers

Consider branching for the carbon skeleton: 1. 2-Chlorines on a branch: - 2-chlorines on the same carbon at branching point, for example, 2,2-dichlorobutane (already considered in linear section as it results in the same structure) 2. Different positions for chloro groups in branched configurations can make distinct isomers, e.g., 2,3-dichlorobutane.

Identify Chiral Isomers

Chirality arises from a carbon atom bonded to four different groups. Among the isomers listed, 1,2-dichlorobutane and 2,3-dichlorobutane have chiral centers causing these molecules to potentially be enantiomers.

Name the Isomers

Provide systematic names: - 1,1-dichlorobutane - 1,2-dichlorobutane (chiral) - 1,3-dichlorobutane - 1,4-dichlorobutane - 2,2-dichlorobutane (repeated by position) - 2,3-dichlorobutane (chiral)

Key concepts

Chirality

Chirality is an important concept in organic chemistry that describes a property of a molecule. A molecule is chiral if it has a carbon atom bonded to four different groups, making it non-superimposable on its mirror image, much like human hands are mirror images but not identical. These mirror-image molecules are called enantiomers, and they are a kind of stereoisomer.
Identifying chiral centers in a compound is essential because chirality can significantly impact the chemical behavior and biological activity of molecules. In our exercise, the isomers 1,2-dichlorobutane and 2,3-dichlorobutane were identified as chiral because they contain carbon atoms with four distinct groups attached. When identifying chiral compounds, look for:

• A carbon atom with four different substituents
• No plane of symmetry through the molecule
• Presence of enantiomers if such a center exists

Systematic Naming

Systematic naming in organic chemistry, also known as IUPAC nomenclature, is a standardized method for naming chemical compounds to ensure that each compound has a unique and clear name. This process involves several steps:

• Identify the longest carbon chain in the molecule as the parent chain.
• Number the carbon atoms in the chain starting from the end nearest a substituent.
• Identify and name substituents (e.g., chloro for chlorine atoms).
• Assign numbers to substituents according to their position on the parent chain.
• Combine these elements to form the full name, arranging substituents alphabetically and using prefixes for multiple identical groups (e.g., di- for two chloro groups).

Applying this to our examples, names like 1,2-dichlorobutane clearly indicate two chlorine atoms at positions 1 and 2 on a butane chain, providing precise identification of the molecular structure.

Organic Chemistry

Organic chemistry is the branch of chemistry that focuses on compounds primarily made of carbon atoms, often in combination with hydrogen, oxygen, nitrogen, and other elements. It is the study of the structure, properties, composition, reactions, and synthesis of organic compounds and materials.
A key characteristic of organic chemistry is the structural complexity and diversity of organic molecules. This complexity arises from carbon's ability to form stable bonds with many other elements, including itself, allowing a diverse range of structures from simple chains to complex rings and three-dimensional shapes.
In the context of our exercise, understanding organic chemistry is crucial for drawing and naming various structural isomers of a molecular formula like \(\text{C}_4 \text{H}_8 \text{Cl}_2\). This involves considering:

• The different possible arrangements of carbon atoms forming the backbone
• The placement of chlorine atoms on these backbones
• The resulting changes in chemical properties or reactivities

Molecular Formula

The molecular formula is a notation that represents the number and types of atoms present in a molecule. It is a compact and straightforward way to convey the essential information about a compound's composition without indicating structural or spatial information.
For example, \(\text{C}_4 \text{H}_8 \text{Cl}_2\) indicates a molecule comprising four carbon atoms, eight hydrogen atoms, and two chlorine atoms. From a given molecular formula, chemists can infer potential structural isomers or different molecules sharing the same formula but differing in arrangement.
When working with molecular formulas, several key aspects should be considered:

• They provide a quick overview of the potential size and mass of a molecule.
• They are the starting point for determining possible structural isomers.
• Each structural isomer, despite having the same molecular formula, can have different properties and potential applications.

Understanding molecular formulas is essential for exploring the vast diversity of organic compounds possible with different atomic arrangements.