Introduction to Organic Chemistry - Structural Isomers (A-Level Chemistry)

Structural Isomers

Structural Isomerism

Types of Structural Isomers

Structural isomers are molecules with the same molecular formula but differing structural formulas.

There are 3 main types you need to know:

1. Chain isomer – these have changed carbon chains. For example, one might be pentane, the other 2-methylbutane.

Introduction to Organic Chemistry - Structural Isomers
Introduction to Organic Chemistry – Structural Isomers

2. Functional group isomers – these have the exact same atoms but these are sorted into a changed functional group. For example but-1-ene and cyclobutane.

Introduction to Organic Chemistry - Structural Isomers
Introduction to Organic Chemistry – Structural Isomers

3. Positional isomers – The carbon chain and attached atoms are the same. However, the functional group is attached to a changed carbon. For example, 1-fluoropropane and 2-fluoropropane.

Introduction to Organic Chemistry - Structural Isomers
Introduction to Organic Chemistry – Structural Isomers

Drawing Structural Isomers

To draw these forms of isomers:

  1. Draw the longest chain described in the name of the compound. Refer back to chapter 72 if you do not remember the different stems used to name carbon compounds of different chain lengths.
  2. Number the carbons. The main chain will be numbered in such a way the substituents are given the lowest number as possible.
  3. Add the functional groups to the carbons described in the name. The carbon to which the functional group is bonded to will be indicated with a number in the name.

Worked example: Draw and name the structural isomers of C4H9OH

Answer:

Introduction to Organic Chemistry - Structural Isomers
Introduction to Organic Chemistry – Structural Isomers
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→What is organic chemistry?

Organic chemistry is the study of compounds that contain carbon and hydrogen, and how these compounds interact with each other and with other elements. Organic chemistry is important in a variety of fields, including medicine, agriculture, and materials science.

→What are structural isomers?

Structural isomers are molecules that have the same molecular formula, but have a different arrangement of atoms. This means that they have different properties and behaviors, even though they have the same number of atoms of each element.

→How do structural isomers differ from each other?

Structural isomers differ from each other in terms of the arrangement of atoms in the molecule. This can result in differences in the physical and chemical properties of the isomers, such as boiling point, melting point, solubility, and reactivity.

→What are some common examples of structural isomers?

There are many examples of structural isomers, but some common ones include:

Alkanes: Structural isomers of alkanes have the same number of carbon and hydrogen atoms, but have a different arrangement of these atoms in the molecule.
Alkenes: Structural isomers of alkenes have the same number of carbon and hydrogen atoms, but have a different arrangement of double bonds in the molecule.
Alcohols: Structural isomers of alcohols have the same number of carbon, hydrogen, and oxygen atoms, but have a different arrangement of these atoms in the molecule.

→Why is it important to study structural isomers in organic chemistry?

Studying structural isomers is important in organic chemistry because it allows us to understand the relationship between the arrangement of atoms in a molecule and its properties and behavior. This understanding is essential in fields such as medicine and materials science, where the properties of organic compounds play a critical role.

→How are structural isomers characterized and differentiated from each other?

Structural isomers can be characterized and differentiated from each other using a variety of techniques, including:

Infrared spectroscopy: This is a technique that uses infrared light to identify the functional groups in a molecule and differentiate between different isomers.
Nuclear magnetic resonance (NMR) spectroscopy: This is a technique that uses magnetic fields to determine the arrangement of atoms in a molecule and differentiate between different isomers.
Mass spectrometry: This is a technique that uses a combination of electrical and magnetic fields to identify the molecular formula of a compound and differentiate between different isomers.

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