Great video! I have trouble explaining these concepts to others and this video and your first NMR video really helped me learn how to explain in a simple straightforward way
In part one, you forgot to mark the concrete value of ppm (frequency) which may confuse us to understand (4:20). Hope you add the relation between ppm and frequency. An excellent video. Thank you for your sharing.
it was really helpful video and your presentation was very effective. could you explain about 2D nmr and x ray crystallography by this type of presentation? it would be helpful.
Great video :) Quick question: If shielded protons generally align slower to the magnetic field after being pulsed, why is it that they appear to have a higher frequency?? I mean, they align slower, therefore spin slower into the aligned state and should have a lower frequency, no? Or is the reciprocal axis inverted?
You have it correct. The high frequency is to the left and the low frequency is to the right. The X-axis is in ppm where ppm = ((frequency of the peak - frequency TMS)/spectrometer frequency) X 10e6. Notice that the left hand side of the axis is large positive numbers and the right hand side is small positive numbers. So it's like the X-axis is flipped. For more on this topic please see chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(McMurry)/13%3A_Structure_Determination_-_Nuclear_Magnetic_Resonance_Spectroscopy/13.02%3A_The_Chemical_Shift
Thanks for your kind words, babayaga. I have tried hard to make improvements to the narration and audio quality...and there's still room for improvement! I would hope that anybody who has trouble understanding would take advantage of the closed captions (CC).
You make the point that neighbor protons don't split each other if they are in identical location environments in the molecule. This presumably is because both electrons resonate at the same frequency and in effect flip together and always remain in the same relative orientation to each other. Can there be the case where some molecules in the sample are not all in the ground state in which case one would see a split. For instance if there are two Ha protons in a molecule they could be anti-aligned in the ground state of the molecule, can there then be an excited state where they are instead aligned and thus feel a different field do to their neighboring Ha? Or, does such an excited state not exist because the molecule would fall apart with this different alignment.
Hi Howard, nuclei in identical environments do couple to each other, however no splitting is observed in the spectrum. When two equivalent nuclei couple, transitions between energy levels do not change because the interactions between the nuclear moments are the same. Please see the NOTE section here: chem.libretexts.org/Courses/Pacific_Union_College/Quantum_Chemistry/14%3A_Nuclear_Magnetic_Resonance_Spectroscopy/14.07%3A_Spin-Spin_Coupling_Between_Chemically_Equivalent_Protons_is_Not_Observed#:~:text=Spin%20coupling%20comes%20from%20a,levels%20of%20allowed%20spin%20states.&text=Spin%20A%20(shown%20in%20red,both%20of%20which%20are%20equivalent. The protons are either aligned with or aligned against the magnetic field, and the NMR spectrum is picking up the energy change when protons flip from one to the other. I don't know about the situation where a molecule is in an excited state and how that would change the nuclear moments. The following presents spin-spin coupling in more detail: chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Analytical_Sciences_Digital_Library/Active_Learning/In_Class_Activities/Nuclear_Magnetic_Resonance_Spectroscopy/03_Text/04_Nuclear_Coupling
