Berea College

This page is the clearinghouse for all of the various blog posts about Nuclear Magnetic Resonance Spectroscopy from our work at Berea College.

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The total echo experiment (which refocuses both J-coupling and Chemical Shift interactions at the same time) allows the user to collect the zero time echo point which otherwise is impossible in a normal Hahn Echo/CPMG/PIETA experiment. When the user wishes to collect a whole echo with each refocus period, you need the TE-PIETA approach (or a comparable total echo approach). The four-dimensional data is reduced by removing the 2 phase dimensions down to a two-dimensional dataset. An example of this reduced data is given in the following <a href="https://bereaedu.wpenginepowered.com/chm/wp-content/uploads/sites/40/2022/03/TEPIETA_2.2Pb_P.2D_Time.pdf">PDF</a> file. Once the 2D FT is applied, we arrive at a dataset that correlates the isotropic chemical shift in the horizontal dimension with the J-coupling in the vertical dimension of this <a href="https://bereaedu.wpenginepowered.com/chm/wp-content/uploads/sites/40/2022/03/TEPIETA_2.2Pb_P.2D.pdf">PDF</a>. Slices through the two types of sites (Q0 and Q1) are shown in this <a href="https://bereaedu.wpenginepowered.com/chm/wp-content/uploads/sites/40/2022/03/TEPIETA_2.2Pb_P.1dProj.pdf">PDF</a>.

[caption id="attachment_91601" align="alignnone" width="300"]<img class="size-medium wp-image-91601" src="https://bereafaust.wpengine.com/wp-content/uploads/2023/02/TE_PIETA-1024x738-1-300x216.jpg" alt="" width="300" height="216" /> Density operator treatment of TE-PIETA[/caption]

[caption id="attachment_91602" align="alignnone" width="238"]<img class="size-medium wp-image-91602" src="https://bereafaust.wpengine.com/wp-content/uploads/2023/02/TE-PIETA_Fig-812x1024-1-238x300.jpg" alt="" width="238" height="300" /> TE-PIETA pulse sequence and coherence pathways[/caption]

PIETA Perfection?

So many organic chemists seem to love showing pure decoupled 13C NMR spectra in papers. I just don’t get it? Why don’t more people use the APT sequence (attached proton test) which causes carbon sites with even numbers of attached hydrogen atoms to point in the opposite direction of those with an odd number? This allows you to quickly distinguish CH2 from CH or CH3peaks. Also to distinguish an aromatic CH from a non-protonated aromatic peak. The only real drawback is that if the C-H J-coupling is not quite normal, you can lose some amplitude. This is not common. The S/N and overall experiment times are very similar to a conventional 13C decoupled spectrum. Here is an example in the image below.

[caption id="attachment_91604" align="alignnone" width="300"]<img class="size-medium wp-image-91604" src="https://bereafaust.wpengine.com/wp-content/uploads/2023/02/Comparison-1024x792-1-300x232.jpg" alt="" width="300" height="232" /> Comparison of different 1D NMR carbon-13 experiments showing that with default parameters the APT is the best[/caption]

How APT are you?

This BLOG will be a clearinghouse for various samples we have studied at Berea College on our JEOL EZCR 500 and our older ECX 300 NMR spectrometers. As an introduction, the author (Jay Baltisberger) was trained as a solid-state NMR spectroscopist at UC Berkeley in the Pines laboratory. His specialty is solid-state experiments on quadrupolar nuclei but he has done research in a broad range of materials. Jay has also taught classes at Berea College on NMR spectroscopy as well as other topics in physical chemistry.

So without further ado, let’s get down to some brass tacks and talk NMR!

NMR Blog