Problem 34 - Chemistry Matter and Change

Question

Draw and name all of the structural isomers possible for an alkyl halide with no branches and the molecular formula \(C_{5} \mathrm{H}_{10} \mathrm{Br}_{2} .\)

Step-by-Step Solution

Answer

There are four structural isomers: 1,2-dibromopentane, 1,3-dibromopentane, 1,4-dibromopentane, and 1,5-dibromopentane.

Step 1: Identify the Base Structure

The molecular formula provided is \(C_5H_{10}Br_2\). An alkyl halide with no branches means we will have a straight chain of five carbon atoms as the backbone.

Step 2: Determine the Placement of Bromine

Bromine atoms can be attached to any of the carbon atoms in this chain. The key is to place the two bromine atoms in different positions to explore all possible unique structures.

Step 3: Draw the Isomers

Begin by placing bromine atoms at all possible combinations of different carbon positions along the 5-carbon chain: 1. 1,2-dibromopentane. 2. 1,3-dibromopentane. 3. 1,4-dibromopentane. 4. 1,5-dibromopentane. Place bromines symmetrically to ensure no repetition and consider the chain from either end to count unique positions only.

Step 4: Name the Isomers

Use the IUPAC naming convention: 1. For carbon position 1 and 2, it's named 1,2-dibromopentane. 2. Moving one bromine over gives 3 on carbon 3, giving 1,3-dibromopentane. 3. Continuing further gives 1,4-dibromopentane. 4. Finally connecting ends is 1,5-dibromopentane, as any orientation here reflects symmetry.

Key Concepts

Alkyl Halide

An alkyl halide, sometimes referred to as a haloalkane, is an organic compound consisting of an alkane with one or more halogen atoms attached. In other words, it is formed when a hydrogen atom in an alkane is replaced by a halogen such as bromine, chlorine, or iodine. Alkyl halides are often used in various chemical reactions and can be found in products like solvents and refrigerants. The presence of halogens increases the reactivity of the molecule compared to plain alkanes.

In our exercise, bromine is the halogen forming the alkyl halides from the pentane structure. This results in compounds like dibromopentane with variations in bromine placement. Understanding the basic structure of alkyl halides enhances your ability to envision possible isomers effectively.

Molecular Formula

A molecular formula is crucial for understanding the composition of a compound. It depicts the number of each type of atom present in a molecule without detailing the exact structure or arrangement of these atoms. In our exercise, the molecular formula given is \(C_5H_{10}Br_2\). This formula tells us that we have a compound consisting of five carbon (C) atoms, ten hydrogen (H) atoms, and two bromine (Br) atoms.

The molecular formula is useful for calculating the molecular weight and helps in deriving other important chemical properties. It allows chemists to predict potential structural isomers and explore possibilities like branching or linear configurations. Understanding the molecular formula provides a strong basis to approach and breakdown the structure of complex molecules.

IUPAC Naming

IUPAC naming rules are essential for systematically identifying organic compounds. The International Union of Pure and Applied Chemistry (IUPAC) provides guidelines to eliminate confusion arising from common names and to maintain consistency across the scientific community. When naming dibromopentanes, the IUPAC rules require that each bromine atom's position is specified using numbers, ensuring clarity in communication.

In the context of dibromopentane isomers:

• Start numbering the carbon chain from the end closest to the first halogen atom for lower numbering.
• The positions of bromine are indicated by numbers before the name (e.g., 1,2-dibromopentane).

Proper IUPAC naming allows chemists to identify the correct structure and placement of atoms in the compound.

Dibromopentane

Dibromopentane is an example of a dibrominated alkane with the molecular formula \(C_5H_{10}Br_2\). Here, the presence of two bromine atoms on a straight pentane chain results in several structural isomers, each unique based on bromine positioning.

Exploring the isomers:

• **1,2-dibromopentane:** bromines are positioned on the first and second carbon atoms.
• **1,3-dibromopentane:** bromines take the first and third positions.
• **1,4-dibromopentane:** one bromine on the first and another on the fourth carbon.
• **1,5-dibromopentane:** both bromine atoms are situated at opposite ends, first and fifth positions.

Each isomer reflects the flexibility and complexity in molecular structure resulting simply from varied bromine placements. Understanding these variations deepens comprehension of isomer chemistry and its implications.