If your samples do not have deuterated solvent, you should run your spectra in unlocked state. In bsmsdisp, uncheck lock (make the button white), then go to “lock” tab and uncheck “sweep on-off” button.
The spectra will not be of the highest resolution because you will not be able to shim using the 2H lock signal. If resolution is a concern to you, you can shim by watching the FID.
Cl and Br have huge quadrupolar moments and their effect to other nuclei in the neighborhood can be considered non-existent.
The effect of 14N is dependent on its electron environment. 3-coordinated 14N has a large asymmetry in electron structure and thus the quadrupolar coupling is large, thus usually has negligible effect to neighboring nuclei. 4-coordinated 14N is more electronically symmetric and has a smaller quadrupolar coupling, therefore can split neighboring nuclei. In this case, the neighboring 13C will be split into a triplet with intensity ratio of 1:1:1. The splitting distance gives you the J-coupling constant between the nucleus of interest and the 14N.
2H has a fairly small quadrupolar coupling so it almost always split neighboring 13C to a 1:1:1 triplet. Those who have run 13C spectra of samples with CDCl3 must be quite familiar with those triplets!
If you use acetone-d6 or dmso-d6 as solvent, the solvent peak on 13C spectra is not triplet but a septulet. Do you know why and can you predict the intensity ratio of the 7 peaks?
31P and 19F have a spin of 1/2 and will always split neighboring nuclei to a 1:1 doublet. If multiple 19F are present in the neighborhood, your 13C peaks will have a more complex splitting.
Quantitative 13C NMR requires full relaxation of all carbons at each scan, which is typically very long (could mean that you have to set d1 to > 100 seconds). Adding paramagnetic chemicals could speed up the relaxation. A common choice is chromium acetylacetonate, or Cr(acac)3. The trick is to add a suitable amount to your solution. Too little, the 13C T1 will not be short enough. Too much, the signal will be broadened too much (because T2 is shortened too much) and you will lose resolution, and you will experience hardship locking and topshim. Between 0.4wt% and 0.6wt% (3 – 4 mg per 0.5 ml of solvent) is typically used. The solution will have a purple color.
Following is a picture of a standard sample with 0.5wt% Cr(acac)3 for your reference. Add Cr(acac)3 so that your sample has a similar color to this.
If your aim is to obtain a quantitative spectrum so you can integrate all peaks with confidence, you should read in parameter set CARBON1. If your aim is to obtain maximum signal strength, you should read in a different parameter set – C13CPD90 (or C13QUANT), which will result in ca. twice as much signal strength as the default CARBON1.
You will notice that the lock line gets quite noisy – this is normal; when chromium speeds up the T1 relaxation, it also speeds up the T2 relaxation, resulting in broader signals. The same effect is also applied to the solvent, resulting in noisier lock signal. If you have trouble doing Topshim, it is likely due to the noisy lock signal. Try manual shimming.
The same applies to 29Si (and especially so since 29Si T1 is even longer than 13C T1) but you should choose SI29IG, which is run without NOE since NOE of 29Si does not enhance signal. You could also choose SI29QUANT. Note: for best results, you will need to add more Cr(acac)3 than 13C experiments. I recommend 8 mg per tube of 0.5 ml solvent.
This document describes how to reserve time on NMR instruments.
This document discusses how to conduct T1, T2, and kinetics experiments. It also covers the processing of data, which can be done in the Dynamics Center.
Bruker NMR’s detect the presence of sample by trying to spin it. If the sample cannot spin, then the bsmsdisp panel will show “sample missing”. After you lock the sample, the lock button will not be green even though it actually has been locked and the scanning line has risen to the upper part of the lockdisp window. You can still run your experiment in this situation.
Spinning improves the resolution of your spectrum to some extent. However, the resolution without sample spinning is usable in most applications.
Related link: When it helps to spin and when not.
Training new NMR users is comprised of two stages. If you are a czar or an experienced NMR user in a group that does not have a czar, you are in charge of the first stage. In the first stage, the trainer explain the safety precautions and demonstrate a couple of time how to run a proton NMR, then ask the trainees to run a couple of samples and provide critiques. This training material (presentation; printer-friendly handout)can be used by the trainer for the most essential training content. If you have developed your own training material, please be sure to discuss safety issues and at least cover the safety topics that I discussed in the above referenced material.
Once you feel that the trainees have become comfortable running a proton experiment and that each of them has become keenly aware of the safety issues, please forward their names to Dr. Hu at weiguoh at polysci umass edu. The second stage of training will be scheduled for them.
All new users of NMR instruments please follow these procedures to obtain an account:
1. Watch this video a couple of times to obtain a visual impression of the experimental procedures.
2. Read the safety precautions in the first four pages of the “workshop1” file in the bottom of this page. Stop and consult the Facility Director if you wear a heart pacemaker or are pregnant; you and the embryo might be harmed by the extremely strong magnet.
3. Receive a hands-on training from a senior NMR user in your group. This link provides a detailed instruction on basic NMR operations – please follow it as you observe the senior user operating and as you operate with the senior user watching. You are not allowed to operate the NMR instrument alone before you pass the exam and are given your own account.
4. When the trainer feels that you have become comfortable running a proton experiment yourself, please ask him/her to forward your name to the Director at weiguoh at umass edu.
5. Read and try to understand all the content in the three workshops below. You can ask senior NMR users and/or search the web for questions. Bring remaining questions to the training sessions.
6. You will need to take two training sessions offered by the Facility. Please contact the NMR TA to request your first training session. The Facility usually offers training sessions twice every month. You will need to successfully pass an exam administered at the end of the second session to get a user account. There are some sample questions on the last page of handout #3.
The following are the handouts. The first session will be taught by the TA of the Facility, offered on the first and third Wednesday afternoon of each month. The second session will be offered by the Director.
Upon loading topspin, it will take a little time to load up the spectrum that you used last time. If you type dir when the screen is still blue, you will confuse topspin.
To solve the problem, go to File -> Open, and find the path that contains your data. It is usually /opt/topspin/data/[your login]/nmr. Open any data file. This will reset the default data file path to your own directory. If you type dir now, you will be able to see your directory.
If it seems to take quite long to load up the last data file once you start topspin, it is likely because you have too many data files. Delete some!