Question

Consider two molecules that are constitutional isomers. (a) What is the same on the molecular level between these two molecules? (b) What is different on the molecular level between these two molecules?

Short answer

(a) They have the same molecular formula. (b) Their atom connectivity or arrangement differs.

Step-by-step solution

Understanding Constitutional Isomers

Constitutional isomers are compounds that have the same molecular formula but differ in the way their atoms are connected or arranged.

Identifying Similarities

On the molecular level, constitutional isomers have the same number of each type of atom. This means they share the same molecular formula, indicating they contain the same atoms in the same overall proportions.

Identifying Differences

Despite having the same molecular formula, constitutional isomers differ in the connectivity or sequence of their atoms. This means their atoms are arranged differently, which leads to different structural formulas and different chemical properties.

Key concepts

Molecular Formula

A molecular formula provides the total count of each type of atom in a molecule. It's like a recipe card listing the exact number of ingredients needed. For example, the molecular formula \( C_4H_{10} \) tells you there are four carbon atoms and ten hydrogen atoms in the molecule. This doesn't, however, give any information on how these atoms are bonded or arranged.
Constitutional isomers have identical molecular formulas. This means they have the same numbers of each kind of atom, making them chemical siblings in terms of ingredients used. However, it is the way these atoms are put together that creates their distinction. This formula is essential for identifying isomers because it confirms that you're comparing structures made from the same atomic building blocks.

• Shows the number of each atom in a molecule
• Identifies chemical siblings (isomers)
• All isomers must share the same molecular formula

Atom Connectivity

Atom connectivity refers to how atoms are connected to each other in a molecule. Imagine a dot-to-dot puzzle, where each dot represents an atom and each line represents a chemical bond. Two molecules may have the same number of dots, but how you connect these dots can create different images.
In constitutional isomers, despite having the same molecular formula, the way atoms are connected varies. This different connectivity results in distinct structures, leading to variations in both physical and chemical properties. Understanding atom connectivity gives insight into how a molecule is structured, influencing its reactivity and behavior in chemical reactions.

• Illustrates the sequence and connection of atoms
• Differentiates isomers with the same molecular formula
• Affects physical and chemical properties of the molecules

Structural Formula

The structural formula is a way to represent the exact arrangement of atoms within a molecule. Think of it as a detailed map, showing not only the elements present (like a molecular formula) but also how they are arranged and linked.
While molecular formulas of isomers look identical, their structural formulas highlight the differences in atom connectivity, leading to unique geometric arrangements. These distinctions can affect a molecule's functionality, resulting in different chemical activities and interactions. By examining the structural formula, chemists can predict a molecule's properties and understand its behavior in various environments.

• Depicts the arrangement and bonding of atoms
• Reveals differences in isomers' connectivity
• Helps in predicting the molecule's properties and behavior