Physical Chemistry II LaboratoryWinona State University
N,N-Dimethylacetamide (DMA) Bond Rotation Activation Parameters by Saturation Transfer
JEOL ECX 300 NMR Procedures
Preliminary. The DMA NMR sample tube has been prepared for you and will have previously been placed in the NMR probe. The Delta software will have been started and the needed windows opened. Allow 10 min for temperature equilibration at each temperature being used.
Obtain 1H spectrum. In the Delta “Sample” Window, make sure the sample is spinning, the solvent is selected as toluene-d8, and the instrument is locked and then manually adjust the Z shim settings (especially Z1 and Z2) for maximum lock signal. In the “Spectrometer Control” Window select <expt> and then “proton”. Enter a file name; for consistency please name as “DMA 1H xx”, where xx is the temperature in ˚C. Set solvent to toluene-d8, set scans to 4 and click <submit>. The spectrum will automatically display when done. Later when the inversion-recovery experiment is running you will want to integrate the spectrum by selecting the integral tool and clicking and dragging in the gray region below the x axis from just before each peak to just after. Print the spectrum by clicking on the plotter icon.
Carry out spin saturation transfer experiment. Inthe “Spectrometer Control” Window select <expt> and then “DMA Saturation Transfer”. Enter a file name; for consistency please name as “DMA 1Hdec xx”, where xx is the temperature in ˚C. Make sure solvent is set to toluene-d8 and set scans to 4>. Make note of all of the irradiation parameters and click <submit>. (Note: unlike the literature reference we are irradiating the peak at 2.6 ppm and observing the B methyl protons’ integral.) The spectrum will automatically display when done. Later when the inversion-recovery experiment is running integrate and plot the spectrum as above.
Carry out inversion-recovery experiment. Inthe “Spectrometer Control” Window select <expt> and then “DMA T1 Measurement”. Enter a file name; for consistency please name as “DMA 1H T1 xx”, where xx is the temperature in ˚C. Check the solvent setting and make sure scans is set to 2 and then click <submit>. This experiment takes around 30 min to run, so go back and integrate and print out the spectra obtained previously during this time. When complete the data will automatically display in the “nD Processor” Window. Click the “X” icon, then “1D slice” and adjust the phase (using P0) on the spectrum in the window that pops up. Close out this window and the phasing parameter just determined is added to the nD processor processing list. Click the “Process file and put in data slate” icon (it looks like 3 peaks with an arrow pointing up) and the Data Slate” Window opens with your T1 inversion-recovery data. (For a better look at the data, try right clicking on the display, hold the click until a menu appears and choose stack.)
T1 Analysis. In the Delta “Master” Window select <Viewers>, <Analysis>, <T1 Analyze>. Click the “finger” icon and then the “open data file” icon (it looks like a floppy disc with an arrow pointing off to the right). Go back to the “Data Slate” Window and click on the spectrum. Now go back to the “T1 Analyze” Window and zoom the peak of interest at 2.6 ppm. Click “By Pick” then click just below the x-axis and drag until the cursor is at the peak maximum. Select the desired curve fitting method, then click the “apply” button. The results display in the small window at right. To print, click the “plotter” icon, then check the desired options to print out and then click the print icon.
Set up for next group. Close out all windows except the first three (Delta Master, Spectrometer Control, and Sample). In the sample window set the target temperature to 5.0 degrees above the temperature at which you were just working.