🇺🇦 nmr_spectroscopy / organic chemistry ⌬

It’s #NMRweekend time! 🧲⁉️ Take part in the poll below 👇. #nmrchallenge #quiz

It’s #NMRweekend time! 🧲⁉️ Can you identify the correct structure based on the spectrum? Take part in the poll below 👇. #nmrchallenge #quiz

It’s #NMRweekend time! 🧲⁉️ Can you identify the correct structure based on the spectrum? Take part in the poll below 👇. #nmrchallenge #quiz

Shining a Light on NMR: Tracking E-Z Photoisomerization ☀️🧪 Light can do amazing things to molecules, and E-Z photoisomerization is one of the most elegant examples of photochemistry in action. When we irradiate this extended conjugated system with 350 nm UV light for just 30 minutes, the molecule absorbs the energy, temporarily breaking the π-bond and allowing it to rotate, flipping its geometry. When it comes to studying these structural transformations, NMR spectroscopy is an absolute powerhouse. It doesn't just tell us that a reaction happened; it gives us precise geometric proof. Take a look at the 1H NMR spectra in the image. By simply comparing the before (bottom) and after (top) spectra, we can easily track the reaction. The ultimate proof comes from the ³J(HH) coupling constants: the characteristic coupling of the double bond protons drops dramatically from 15.0 Hz (typical for the E-configuration) down to 11.1 Hz (confirming the newly formed Z-isomer). It’s a clean, direct, and incredibly convenient way to monitor the process! ⚠️ A crucial reminder for the lab: This beautiful phenomenon is exactly why you must ALWAYS consider the photostability of your compounds when preparing NMR samples. Isomerization isn't the only risk—ambient light can trigger unwanted photodegradation, cyclizations, or oxidations. If you leave a clear glass NMR tube with a light-sensitive compound on a sunny lab bench or under bright fluorescent lights, your sample might be ruined before it even reaches the magnet. If your molecule is photoreactive, always wrap your tubes in foil, use amber NMR tubes, or prepare the sample immediately before the experiment! #nmrchat #photochemistry #isomerization #alkene Want to see the full picture? Resolving the exact signals of this isomeric mixture required a bit more digging. If you want to see the 2D NMR spectra (HSQC and COSY) that I used to unambiguously assign every single peak—welcome to my Substack!

It’s #NMRweekend time! 🧲⁉️ Can you identify the correct structure based on the spectrum? Take part in the poll below 👇. I’ll post the full explanation in a few days. 😉 #nmrchallenge #quiz

The hidden order behind a complex multiplet 🧩 At first glance, this ¹⁹F NMR signal might look like a chaotic forest of peaks, but it’s actually a beautiful demonstration of a higher-order XX'AA'MM'NN'R spin system. Why does a simple molecule produce such a complicated pattern? It all comes down to the crucial difference between chemical and magnetic equivalence. Thanks to the molecule's plane of symmetry, the two fluorine atoms (and their neighboring protons) are chemically equivalent. However, because they are locked in a rigid cyclic structure, each fluorine interacts (couples) differently with the other protons across the ring depending on their spatial distance and geometry. This magnetic non-equivalence, combined with the diastereotopic CH2 protons in the ring, turns what would be a simple signal into this intricate, perfectly calculable pattern. As you can see, the experimental spectrum matches the calculated one flawlessly! Find this and other building blocks at enaminestore.com #NMR #FluorineNMR #spinsystem

It’s #NMRweekend time! 🧲⁉️ Can you identify the correct structure based on the spectrum? Take part in the poll below 👇. #nmrchallenge #quiz

How Much Sample Do You Need for NMR? A Practical Guide From standard 1D proton spectra to low-concentration 2D experiments: sample requirements for optimal signal-to-noise. 👉 full post on my Substack!

It’s #NMRweekend time! 🧲⁉️ Can you identify the correct structure based on the spectrum? Take part in the poll below 👇. I’ll post the full explanation in a few days. 😉 #nmr #nmrchat #chemistry #quiz

In today’s #NMRMultiplet we’re going to consider this complex 1H NMR signal from a norbornane derivative (centered at 2.23 ppm, labeled (tdd). 🔍 Feature Highlights: 1️⃣ Distinct W-Coupling (4J): Highlighted with the red curved line in the picture is a clear 4J(H,H) W-coupling (approximately 3.5 Hz) to a bridge syn-proton. The unique rigid skeleton provides the ideal geometry for this strong long-range “W” interaction. 2️⃣ Negligible Bridgehead Coupling (3J): Notice that there is no 3J coupling to the adjacent bridgehead proton. This is a classic Karplus relationship in action: the dihedral angle between this target proton and the bridgehead H is approximately 90°, predicting a vicinal constant near zero. 3️⃣ Decoding the rest: The other three couplings in our splitting tree are: 14.67 Hz, 14.67 Hz, and 11.13 Hz. They come from vicinal 3J(H,F) interactions and a geminal 2J(H,H) pairing. #coupling #norbornane

It’s #NMRweekend time! 🧲🧩 Can you identify the correct structure based on the 1D NOESY spectrum? (Honestly, the ¹H NMR alone is enough to crack this one 😉). Take part in the poll below 👇. I’ll post the full explanation in a few days! #nmr #nmrchat #chemistry #quiz