Basically, my question is can you used a non-deuterated solvent for 13C NMR? I'm thinking that there might be some problems with locking?
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2$\begingroup$ On top of long's answer, I would just mention that you can use nondeuterated solvents even for ordinary 1H NMR. (This is already implied in the answer.) Ideally, you'd pick a solvent which doesn't overlap with your peaks of interest; and the solvent suppression techniques (routinely used with H2O samples) will be useful too. $\endgroup$– orthocresolAug 28, 2020 at 6:44
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2 Answers
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If using a deuterium lock, then normally you would require, as minimum, about 10% deuterated solvent. Without any deuterated solvent, it is not possible to obtain a spectrometer lock (unless using a 19F lock channel, but that is unlikely, and is a hardware requirement).
It is, however, perfectly feasible to acquire spectral data for all nuclei without any deuterated solvent, and hence, without a spectrometer lock. When running without a lock, you need to turn the lock sweep off, to hold the spectrometer field constant. This does not provide the same level of field stability as a lock, but is more than adequate for short-medium 1D experiments that do not require very high resolution. Using gradient shimming, it is also possible to shim on non-deuterated solvents and achieve the same lineshape specifications. Running long experiments (such as an overnight 13C{1H} experiment), without a lock will give you linewidths that are slightly broader than usual; the consequences of this are that (i) your resolution is reduced (rarely a problem with 13C), and (ii) your signal-to-noise will be reduced (and therefore longer experiment times may be required...leading to further broadening and longer experiment times...)
Not claiming to be the first to report about this technique, the Hoye group published two papers in Organic Letters (2004OL953 and 2004OL2567) with examples of application of no-D $\ce{^1H}$-NMR spectroscopy, covering sample preparation and data acquisition, too. Especially the second one, outlining how to determine the concentration of LDA or Grignard reagents by addition of 1,5-cyclooctadiene as internal standard may be a reliable and faster alternative to the titrations once you are used shim manually for samples of this type. But speak and obtain clearance in advance with your NMR manager before running your no-D sample; some interfaces to the spectrometer tend to be less puzzled to record NMR with a lock after your sample (e.g., elder Varian), than the more modern (e.g., Topspin Bruker) to prevent unnecessary delays in the queue of samples following yours.
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1$\begingroup$ In groups where recording NMR spectra by your self is permitted / assumed, recording no-D 1H-NMR may be something as normal as recording your «normal» 1H-NMR spectrum. Thus I thought the addition of the two Hoye papers were beneficial to your answer given. $\endgroup$ Aug 28, 2020 at 16:41
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It is indeed possible and you will indeed have problem with locking. My solution is to use sealed capillaries with a deuterated solvent inside. This procedure allows you to lock without having the solvent in your mixture.
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$\begingroup$ This is an interesting approach, can you provide additional details or citations for those of us not familiar with the technique? Does it require specialized NMR tubes? Can this help in situations where peaks are lost due to rapid H-D exchange? $\endgroup$ Aug 28, 2020 at 16:37
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1$\begingroup$ @dissemin8or You may use already a normal NMR tube with a capillary containing your e.g., deuterated trifluoroacetic acid. Depending on the sensitivity of the NMR spectrometer, a about 5 cm partially [80%] filled, but flame sealed (e.g., by a lighter) melting point capillaries already may do the job. This isn't too much weight added and may be used multiple times. Indeed, this will prevent H-D exchange completely. (H-D exchanges may be slowed in dry DMSO-d6, too.) Schematic example $\endgroup$ Aug 28, 2020 at 17:00
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$\begingroup$ @dissemin8or I use normal NMR tubes (5mm) and capillary for melting point determination closed on one side (dimensions 1.55 mm diameter, 75 mm lenght) i fill them in a way that no air is contained in the measuring zone but you have to leave a bit of space for flame seal them. As already mention you can add up to two of them (in this way you even reduce the volume of solution needed in your measurements), my experience is that with C6D6 one is more than enough but when you go for a solvent with less deuterium content like CDCl3 you most likelly need two. $\endgroup$– M SSep 1, 2020 at 7:26