Back to: Organic Chemistry 400 Level
Welcome to class!
Hello brilliant learner, I’m really excited to be with you again today. I believe you’re focused and ready because what we will learn today — Advanced Spectroscopy I — is one of the most powerful tools used by modern chemists to identify and study organic molecules. You will soon discover how we can “see” inside a molecule without touching it, simply by studying the way it interacts with different forms of electromagnetic radiation.
Advanced Spectroscopy I
Imagine visiting a hospital for a medical check-up. Instead of opening up your body, the doctor uses an X-ray or MRI machine to examine what is going on inside. In the same way, chemists use spectroscopy to investigate the structure and properties of molecules without destroying them.
Meaning of Spectroscopy
Spectroscopy is the study of the interaction between matter and electromagnetic radiation. When molecules absorb or emit light of a particular wavelength, they move to different energy levels. By studying these energy changes, we can obtain valuable information about the structure, bonding and functional groups present in a substance.
Electromagnetic Spectrum in Spectroscopy
The electromagnetic spectrum covers different types of radiation such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
Each region gives different types of information:
Infrared (IR) Region: Gives information about functional groups.
Ultraviolet-Visible (UV-Vis) Region: Helps determine conjugated systems.
Radio Frequency Region: Used in Nuclear Magnetic Resonance (NMR) to study atomic environments.
You can think of it like visiting different markets in Nigeria to buy specific items — you go to Mile 12 for fruits, Alaba Market for electronics, and Balogun Market for fabrics. Each market gives different types of products just like each region of the electromagnetic spectrum gives different types of information.
Ultraviolet-Visible (UV-Vis) Spectroscopy
UV-Vis spectroscopy measures the absorption of ultraviolet or visible light by molecules.
Molecules with conjugated double bonds absorb light in this region.
The more conjugated the system, the longer the wavelength absorbed.
For example, β-carotene (found in carrots) has a long chain of conjugated double bonds and therefore absorbs visible light and appears orange.
Infrared (IR) Spectroscopy
IR spectroscopy is used to identify functional groups in a molecule.
Each bond in a molecule absorbs IR radiation at a particular frequency, producing a characteristic peak.
For example, the O–H bond in alcohols gives a broad peak around 3200–3600 cm⁻¹, while C=O groups show a strong peak near 1700 cm⁻¹.
You can compare this to hearing different musical instruments during a performance. Even with your eyes closed, you know when the talking drum, flute or shekere is being played because each has a unique sound — in the same way, each functional group has a unique absorption signal.
Importance of Spectroscopy
It allows chemists to determine the structure of unknown compounds.
It is non-destructive and does not consume the sample.
It is widely used in pharmaceuticals, food quality analysis and research laboratories.
Summary
- Spectroscopy is the study of how molecules interact with electromagnetic radiation.
- Different regions of the electromagnetic spectrum provide different information about molecules.
- UV-Vis spectroscopy is useful for identifying conjugated systems based on light absorption.
- IR spectroscopy helps detect functional groups by analysing their characteristic absorption bands.
- Spectroscopy is a non-destructive method that is vital in chemical analysis and research.
Evaluation
- What is spectroscopy?
- Name two regions of the electromagnetic spectrum used in organic spectroscopy and state one application of each.
- Explain why β-carotene absorbs visible light.
- What functional group gives a strong IR absorption near 1700 cm⁻¹?
Fantastic job today! You are growing in strength and knowledge every single day. Keep learning, keep believing in yourself, and stay connected to Afrilearn — the next lesson will take you even deeper in this exciting area of chemistry!