Spectroscopy

This section has tutorials on various types of spectroscopy we typically see in an Organic Chemistry course. Here, you’ll find tutorials on:

NMR (Both proton and carbon)
IR
Mass Spectrometry (in development)

Why we bother with spectroscopy

At some point, every organic chemist runs into the same problem: you’ve made something, but how do you prove what it is? That’s where spectroscopy comes in. No single method gives you the full structure, but together they let you reconstruct a molecule piece by piece. Mass spectrometry tells you the molecular formula, infrared (IR) identifies functional groups, and NMR fills in the detailed framework of how atoms are actually connected . In other words, spectroscopy turns an invisible molecule into a set of clues you can interpret.

The key idea is that molecules interact with electromagnetic radiation in predictable ways depending on their structure. By measuring those interactions, we’re not “seeing” the molecule directly—we’re reading its fingerprints. When you combine MS, IR, and NMR, you can confidently determine even complex structures, which is why spectroscopy is at the core of everything from routine lab work to drug design.

Mass Spectrometry (MS)

Mass spectrometry answers a very simple but critical question first: what is the molecular formula? It works by ionizing molecules and measuring the mass-to-charge ratio of the resulting fragments. The molecular ion peak gives you the molecular weight, and the fragmentation pattern provides additional structural hints.

In practice, MS is your starting point. It narrows down the possibilities dramatically before you even look at other data. For example, knowing whether your compound is C₅H₁₂O or C₅H₁₀O₂ immediately changes how you interpret everything else. However, MS doesn’t tell you connectivity very well, it gives you pieces, not the full map. That’s why you don’t stop here; you use MS as the foundation for everything that follows.

Infrared Spectroscopy (IR)

Infrared spectroscopy tells you what functional groups are present. Molecules absorb IR radiation by vibrating (stretching and bending bonds) and different bonds absorb at characteristic frequencies. A carbonyl, an OH group, or an alkene each has a recognizable “signature” in the IR spectrum.

This makes IR incredibly useful for quickly identifying key features. You can often answer questions like: “Is there a carbonyl?” or “Is this an alcohol or an ether?” within seconds. That said, IR doesn’t tell you how those groups are connected or how many of them there are. It’s more like a checklist than a full structure. That’s why IR pairs naturally with MS (formula) and NMR (connectivity) to complete the picture.

Nuclear Magnetic Resonance (NMR)

NMR is where things get detailed. It gives you a map of the carbon–hydrogen framework . Instead of just telling you what functional groups exist, NMR shows how atoms are connected by analyzing how nuclei (like ¹H and ¹³C) behave in a magnetic field. Each unique environment produces a distinct signal, so you can count different types of hydrogens or carbons and see how they relate to each other.

What makes NMR so powerful is the amount of information packed into a single spectrum. Chemical shifts tell you about the electronic environment, integration tells you how many hydrogens are present, and splitting patterns reveal neighboring atoms. Put together, this lets you reconstruct the molecular skeleton. That’s why NMR is typically the first technique organic chemists reach for when determining structure—it turns abstract data into a workable blueprint of the molecule.

Click on the link below to explore the topics.