Back to: Organic Chemistry 400 Level
Welcome to class!
Hello brilliant learner, I’m excited to connect with you again today. I hope you’re feeling confident and ready, because this lesson — Spectroscopy & Structure Elucidation — will bring together everything you’ve learnt about spectroscopic techniques and show you how they are combined and interpreted to determine the structure of unknown organic compounds. This is one of the most important skills in advanced organic chemistry and is the same approach used by research scientists across the world.
Spectroscopy & Structure Elucidation
Imagine receiving a gift that is beautifully wrapped. To know exactly what’s inside, you would look for clues: the weight, the texture of the box, maybe even a small opening. In chemistry, spectroscopic techniques offer those clues. By carefully analysing them together, we can confidently identify the molecule inside.
Combination of Spectroscopic Techniques
Different spectroscopic methods provide different types of information about a molecule:
UV-Visible Spectroscopy tells us whether the compound contains conjugated double bonds or aromatic systems.
Infrared (IR) Spectroscopy identifies functional groups like –OH, C=O and –NH by their characteristic absorption bands.
¹H and ¹³C Nuclear Magnetic Resonance (NMR) Spectroscopy provides information about the number and environment of hydrogen and carbon atoms in the molecule.
Mass Spectrometry (MS) gives the exact molecular weight and characteristic fragment ions.
By combining the data from all these methods, the full structure of the compound is revealed — just like solving a puzzle using different pieces.
Steps in Structure Elucidation
Determine the Molecular Formula
From the molecular ion peak in the mass spectrum and the isotopic pattern, you can calculate the exact molecular weight and deduce the molecular formula.
Identify Functional Groups
Use the IR spectrum to identify key functional groups such as alcohols (broad peak 3200–3600 cm⁻¹), carbonyls (sharp peak around 1700 cm⁻¹), and amines.
Analyse NMR Data
Chemical shift tells you the type of hydrogen/carbon present.
Integration gives the number of protons contributing to each signal.
Splitting pattern shows how many adjacent protons are nearby.
These three pieces allow you to build fragments of the molecule.
Piece Together the Fragments
Combine the fragments obtained from NMR with the functional group information (IR) and molecular formula (MS) to draw the possible structure.
Importance of Structure Elucidation
Structure elucidation is critical in:
Natural product chemistry
Drug discovery and development
Quality control of pharmaceuticals
Forensic investigations and environmental analysis
Without accurate structure determination, it would be impossible to develop safe and effective modern medicines.
Summary
- Structure elucidation requires combining information from several spectroscopic techniques.
- UV-Vis detects conjugated systems; IR identifies functional groups.
- NMR provides detailed information about hydrogen and carbon environments.
- Mass spectrometry gives the molecular formula and fragmentation pattern.
- These data are pieced together to propose and confirm the full structure of the molecule.
Evaluation
- Mention two spectroscopic techniques and state what information each provides.
- What does the molecular ion peak in a mass spectrum represent?
- In NMR, what information does the splitting pattern give?
- Why is structure elucidation important in drug discovery?
You’re doing amazingly well — keep going! Afrilearn is proud of your commitment to mastering organic chemistry, and your next lesson will take you even closer to becoming a confident and independent scientific thinker!