Nuclear Magnetic Resonance Facil

Chemistry Department Nuclear Magnetic Resonance

Spectroscopy (NMR) Facility

Step by step procedure for obtaining ¹H and ¹³C NMR spectra using the 300 MHz UnityInova Varian NMR instrument

After you obtain training and become certified NMR user you will be allowed access to 300 MHz NMR instrument located in Disque 205. You can get a key for Disque 205, which MUST be signed out on the sign out sheet, both located in the Chemistry Dept. main office (Disque 305).

Once inside Disque 205, sign the log book and fill out the time and your choice of measurement parameters. Remove all metallic objects from your person, including watches, keys, cellular phones, as well as any credit cards or other objects containing magnetic strips.

Place the NMR tube containing the sample to be measured in a spinner. You MUST gauge your sample by placing the sample tube firmly in the spinner, and then placing the spinner in the gauge. Press the NMR tube down until the bottom of the tube just touches the bottom of the gauge

Log onto the SUN Microsystems computer with the appropriate user name and password, provided to you during NMR training. Upon logging onto the system, the Solaris CDE 1.3 desktop screen should appear, similar to that shown in Figure 2.

When you have successfully logged in, simply click on the “Software” icon in the bar at the bottom of the screen to open VNMR6.1B software (see Figure 2). Once the software is opened, three new windows should appear, as shown in Figure 3.

Figure 3: Screen-shot showing the VNMR software windows which appear once the program is started.

In the VNMR software, you will see two rows of command buttons, located just above the ‘black’ space. Click on the “Acqi” button. This will bring up a new ‘Acquisition’ window on the right side of the screen as shown in Figure 4.

Click on “Eject,” in the ‘Acquisition’ window, which will cause the ejection of the NMR standard from the central barrel of the magnet (shown in Figure 5 below). You will immediately hear a “hissing” noise.

Remove the NMR standard, and replace it with your already prepared sample. The tube and spinner will hover at the top of the barrel.

In the Acquisition window, click on “Insert,” to automatically insert your sample into the upper barrel of the magnet.

While still in the ‘Acquisition’ window, click on “LOCK” to open the lock window, which will appear on the right side of the screen, as shown in Figure 6.

In the lock window, you will see adjustable parameters, ‘ZO,’ ‘lockpower,’ ‘lockgain,’ ‘lockphase,’ and ‘spin.’ In order to adjust these parameters you can either drag the slide bar using left mouse button or you can click on the number button (clicking with the left mouse button on the specific number button will decrease the value of the specific parameter while clicking with the right mouse will increase the value of specific parameter.) Set the ‘spin’ to 20 Hz. You will immediately hear that spinner pneumatic valve opens.

Next, adjust the ‘ZO’ parameter using the slide bar, to obtain a lock on your sample (there should be a list of ‘ZO’ values for various solvents on the computer desk, which will give you a good starting point). Still in the ‘Acquisition’ window, drag the slide bar either left or right until you notice a wave-like pattern developing, as shown in Figure 7. In order to obtain a lock on your sample, you must minimize the number of wave crests, thereby maximizing the period of the wave.

Figure 7: Screen shot of the lock window, clearly showing the wave-like pattern of the lock signal.

When the lock signal displays only one crest, a slight adjustment will result in a step in the signal, as shown in Figure 8. This is an indication that your sample is locked. If you do not see this step-like pattern arise, you may need to increase the ‘lockpower’ by dragging the slide bar to the right. It is crucial to have the lowest lock power possible, while still exhibiting a step-like lock signal, to achieve the best results. Click on LOCK-ON button.

Adjust the ‘lockphase’ until the lock signal is a maximum (typical lockphase values for various solvents should also be listed on the chart with the ‘ZO’ values).

Click on “SHIM” icon at the top of the ‘Acquisition’ window. The window seen in Figure 9 will appear. You will need to optimize lock level by adjusting Z1 and Z2 shims. Start by adjusting course, Z1C and Z2C in small increments (±1), and then adjusting fine Z1 followed by Z2 in larger increments (±16 or ±64). If you are having problems with shimming, you can recall your previously saved ‘good’ shim files by typing in the VNMR command window:

After the lock is maximized, click on the “CLOSE” button, and proceed to the next section, ‘Acquiring a Spectrum.’

After closing the LOCK window in step 7 of section III., click on the “Main Menu” button (see Figure 10).

Click on the “Setup” button followed by “Nucleus, Solvent” button. Click on “H1” to proceed with a ¹H NMR experiment, or “C13” to run a ¹³C NMR experiment. Select the appropriate solvent, e.g., “CDCl3,” “Benzene,” “D2O,” depending on the solvent you are using. Type in the number of scans you wish to do. For example, type nt = 16 into the command window. (For ¹³C experiments, a higher number of scans is desirable). Press ENTER on the keyboard.

Type ga, and then press ENTER to begin acquisition. If an error message appears during sample acquisition, simply type aa, and then press ENTER. This will abort the acquisition.

To remove your sample, click on “Main Menu” and open the “Acqi” window. Click on “Eject.” Your sample will immediately be ejected from the central barrel on the top of the magnet. Remove your sample from the barrel, and replace it with the NMR standard that was previously removed. Click on “Insert” to insert the NMR standard. Click on “LOCK” to open the lock window. Turn both “lock” and “spin” OFF, by clicking on the respective “OFF” buttons. Close the lock window.

Click on “Main Menu” , “More.” and then “Exit VNMR” to close the software. Click the right mouse button, followed by “log off” to exit the system.

This manual was written by chemistry graduate students Thomas Measey, Andrew Hagarman, and Alma Pipic.

Type ft to Fourier Transform the spectrum, and wft to weigh and Fourier Transform the spectrum.

Type aph to automatically phase the spectrum. Click on "Phase" to phase the spectrum manually.

Type dscale to get frequency scale. Type in axis='h' for Hertz; axis='p' for ppm.

To integrate your spectrum, click on “Part Integral.” If the integral does not have a flat baseline, you can adjust it manually by clicking on “Lvl/tlt.” With the left mouse button, click on the left-most integral and drag it up to increase the slope, or down to decrease the slope. Click on the right-most integral and drag it up or down to get the integral slope as close to zero as possible. Click on “Cursor/Box.” Expand around a desired region for integrals. Click on “Expand.” (Type vsadj to vertically adjust your spectrum). Click on “Resets.” Starting from the left click with the left mouse button around each desired peak. (Full line represents integrated and dashed line non-integrated areas). When finished with the expanded region click on “Full,” and repeat this procedure for the next region(s) of interest. If you want to reference your integral, choose a peak for which the number of protons is known. With the left mouse button, click on the center of that peak, and click on “Set int.” Then, type the number of the protons. To view your integral values, set vp to 12 or larger number and then type to display integral values dpir.

To set the peak threshold, click on “Th.” With the left mouse button, click and drag the yellow line just bellow the smallest peak you want to display. To display your peak values type dpf. If you want to a display peak list type dll.

To print your spectrum, click on “Main Menu,” followed by “Autoplot.” This will automatically send your spectrum to the printer. If you want to print the peak list frequencies as well type pll page.

To save your spectrum, click on “DATA/Data/Save FID,” and then type in a name for the file. To save it as a jcamp file type svsj and type in a file name.