1APPENDIX 2 Version of 8/24/05 11:45 AM Guidelines to operate Varian Mercury Plus for getting a 1H NMR Mircea D. Gheorghiu Please note that a GOOD sample will produce a good lock signal and good 1H and 13C NMR spectra. If the sample is bad, the instrument is unable to do miracles. There are 4 steps in order to get an NMR spectrum. 1. Making a good NMR sample. 2. Getting a good lock signal and shimming the instrument. 3. Acquiring a 1H and 13C NMR. 4. Printing your results. STEP 1: MAKING A PROFESSIONAL NMR SAMPLE: · In a small vial or test tube check if your compound dissolves in a non deuterated solvent (for example CHCl3). · If the preliminary test is satisfactory, dissolve 10-20 mg of your compound in 0.5 – 0.7 mL NMR solvent (the amount in the ampoule) in a separate vial. NMR solvents are deuterated (for example CDCl3) and very expensive. · If the sample is clear (homogeneous) after some swirling (agitation), transfer the it to a clean and dried NMR tube (without traces of washing solvents like acetone, ethanol, etc). · Make sure that the NMR tube is not scratched, cracked or chipped. · If the solution is not clear, filter it through a pipet filter. Insert a small wad of glass wool or a small piece of crumpled of a crumpled KimWipe into the neck of a Pasteur pipet. Place the narrow end of the pipet into the NMR tube. Be careful not to break the upper part of the NMR tube. Transfer the unfiltered solution into the pipet filter with a second Pasteur pipet. If necessary, a bulb to force the solution into the NMR tube. Carefully cap the tube.2STEP2: GET A LOCK SIGNAL. A. Inserting the NMR sample. The sample is rotated at a frequency of 20 Hz inside the magnet. The rotation brings about extra magnetic homogeneity to the sample. · Before ejecting the previous sample that has been left into the instrument (there is always a sample in the NMR probe) make sure that the spinner is off by checking the Acquisition Status window. · To eject the sample and to recover the spinner (turbine), click on Acqi button in the Menu buttons window,: Then click on SAMPLE eject: · Remove the sample that is currently in the probe. · Carefully insert your sample tube into the spinner.3· Clean the outside of the NMR tube with a KimWipe. · Position the tube into the spinner with the depth gauge. · Climb the ladder to reach the top of the magnet and carefully position the tube & spinner on the air cushion that flows through the top NMR probe. · Click on insert. · Set the spinner rate to 20 Hz by clicking the Lock button in the Acqi window and adjusting the bottom parameter.4 B. Getting the Lock Signal. Option #1 will automatically lock and shim, and run the experiment to produce the1H NMR spectrum (e.g. STEP #3 inclusive!): To obtain a 1H NMR spectrum by this methodClick on Walkup tab in the Tcl/dg window, which is present on the bottom left area of the monitor. If you do not seethe Walkup button, then expand the window. · Select the appropriate (lock) Solvent. From the drop down Solvent menu (for example, CDCl3). · Click on H NMR if you want to run a proton NMR. · If the experiment does not start automatically, click the Start ACQ button. 1 Tcl: Tool Command Language, version of the dg program. (that displays group of parameters)5· Shimming, spectra acquisition, and plotting will be done automatically To obtain the spectra manually, use Option #2. Option #2 in which you will learn manual locking2 and shimming3 and 1H NMR. A. To lock: Click on the Acqi Tab and the Acquisition window will appear. · Click on Lock button. Check that the LOCK is off. Initially the spinner is off. Set the spin to 20 Hz by clicking on 16 with the right mouse button (to increment the parameter) and then on 4 with the right mouse button. The SPIN is now on. The left mouse button is used to decrement the parameter 2 In order to maintain the magnetic field at a constant value during the experiment, one must lock the instrument. 3 A good shimming is making the magnetic field as homogeneous as possible. You will get very narrow lines in the NMR spectrum.6 · Increase the lockpower4 to 20 (+16+4) and the lockgain to 28 (+16+16-4). · Adjust the magnetic field frequency Z0 shim (buttons are in Hz units), until a sine wave is seen. The greater the number of sine waves, the poorer the match of Z0 with the deuterium resonance field. 4 The lock power and lock gain levels depends on the concentration of the deuterated solvent, the number of deuterium atoms in the solvent and the relaxation time of the deuterium in that particular solvent.7 · If the lock is near resonance, the wave looks like:8 · If the amplitude is too low, increase the Lock Gain, and, if necessary the Lock Powder5, until the signal is between 50% and 100%. · Continue to adjust Z0 until one wave wavelength is seen: · Click the Lock on button and the lock step function appears. 5 A too high Lock Power (>40) is saturating the lock signal. Saturation is signaled by the fact that the lock level is very erratic. Large values for Lock Gain gives a noisy lock signal. Reduce Lock Powder and adjust Lock Gain to maximize the lock level.9 · If phase is not set properly, adjust the lockphase in steps of –1 or +1. You will notice that the lock signal is maximized. · If the signal appears to be saturated (>= 100), decrease the Lock Gain. B. Shimming. Shimming adjusts the current flow through a series of coils (differently shaped) that surround the NMR sample. Here, only the “spinning” (e.g. the sample is spinning) shims, Z1 – Z7 will be adjusted. In the ACQUISITION window click on SHIM. The following window pops up. · Start increasing (or decreasing) in steps of 1 or 4 the values of Z1C, Z2C, Z1 and Z2 such as to maximize the lock signal.10 · When the lock signal goes above 100%, reduce the Lock Gain in the same window (or if necessary the Lock Power in the Lock window). · In the command line type su, which sets up the lock and shim parameters and disconnects from the Acqi window.11STEP 3: ACQUIRING A 1H (AND 13C NMR). · Select Main Menu, Setup, the appropriate Nucleus and Solvent. · For the 1H NMR, nt=8, is a good choice (nt stands for number of transients (or acquisitions)). · Type ga to acquire and automatically process your spectrum. · After the transitions are completed, the spectrum will be displayed