Terribly formatted poll!
I just took an NMR in acetone-d6, and I thought it'd be interesting to ask everyone:
(Apologies for the awful formatting. It's Blogger's fault.)
2/22/2007
(Apologies for the awful formatting. It's Blogger's fault.)
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19 comments:
My least favorite solvent peak is dichloromethane. It screws up the phasing of the entire proton spectrum...
I almost said DMSO, only because if I want to recover what I've just taken an NMR of, it can be a pain. But if my NMRs don't work out quite right in other solvents, DMSO is like the wonder-solvent.
I'll go with DMF, just because I really hate that shit.
I don't know how anyone could hate CDCl3. You could dissolve anything in that stuff!
d6-DMF is realy expensive, so is CD2Cl2.
I am a fan of DMSO if one does not have to recover the material afterwards and if the coordinating properties/nucleophilicity do not interfere. Nice thing about solvents producing nice sharp symmetrical multiplet in proton spectra is that you can look on the solvent peak and see right away if you got a good resolution or phasing. Also one does not have to guess which of his signals is solvent peak, like with CDCl3. The downside a is relatively broad H2O signal at 3.3-3.4, which tends to get into signals of lotsa things.
naffer: make perylenedibrickdust with the wrong side chains, and it'll take you 15 minutes to get a proton in CDCl3 ;)
i don't know why noone's picked acetone yet. Takes forever to shim.
i'm a p-chemist, so i need an organic chemist to help me take nmrs
I know it's a disgusting solvent - but have you tried d5-pyridine for your perylene pigments?
sam: OK...how about you take my spectro exam, and I take your NMRs? :)
milkshake: I don't know if we even have pyridine-d5 around the lab. I'll keep it in mind, though, should I happen to tack on the wrong alkyls again. Toluene-d8 is my next resort.
toluene-d8 is painful to shim as well. I've found, however, that on a good spectrometer I can get away with putting insoluble perylene-like things in benzene and getting an ok spectrum with it. Gives you an excuse to use the Rolls-Royce NMR's that you can't otherwise justify using.
What is this problem with shimming? Acetone, CD3CN etc. are _slower_ to shim but there is less noise and it is easier to shim the X and Y coils as well... patience, patience makes you a perfect shimmer!
My favourite solvent is CD3CN. No acids, dissolves almost anything, great carbon window, available in high purity, not highly volatile but readily removed by rotavapping.
We have routine gradient autoshim on both our instruments. (One has an autosampler, too.) No signups are needed during the day - there is always access, even with 20-40 samples per day (people run their carbons overnight). The autoshim + ATM procedure makes life much easier.
(What really complicates shimming is when you come to the instrument after somebody who did not know how to shim and messed with the instrument and put the parameters are completely off.)
gradient autoshim is lovely, but in a department large as ours, it's sometimes not to be worth the time it takes to autoshim since the instruments with the feature tend to have heavy traffic during the day.
I might be an impatient shimmer but I've never had a spectrum look right when taken in acetone. I stay away from it, use DMSO instead. I don't mind methylene chloride much either.
Assuming that the earlier user has shimmed well to CDCl3, with some practice, it usually takes much lesser time to manually shim to almost any solvent than autoshim.
What I don't understand is why people have trouble manual shimming in the first place. I wish I knew what they did to get it so painfully out of phase in the first place. (Have I mentioned I don't really like fixing things I didn't screw up?)
I hate acetonitrile because of the super-long relaxation time.
Chloroform has a really long relaxation time and this is good. You don't want your residual solvent taking up a whole lot of space. I don't like it however, since it doesn't resolve aromatic peaks all that well. For an aromatic compound it's better to go with pretty much anything else. DMSO sucks because you can't get stuff back from it in reality (only in theory do you dry a DMSO sample). However, it will dissolve almost anything, so there is that to like.
The one I hate the most would be either D2SO4 (why bother? use DMSO instead of that thick slurry of doom), or CF3CH2OD. Ah, the poor chemist's version of super expensive CF3CD2OD. Not only is the partially deuterated trifluoroethanol impossible to shim at all, regularly giving artifacts out of hell, you can pretty much also say goodbye to the region of your spectrum at 3.5 ppm where the CH2 quartet shows up. Of course, you can use solvent suppression to make it easier on the eyes, but say goodbye to the region at +/- 1 ppm of the CH2 signal anyways.
Evgeny: Really? (re: resolution of aromatics in CDCl3) Not that it matters for me, since I'm only cleared to work on the low-field NMRs anyway.
I also appreciate the phrase "thick slurry of doom." :)
Yeah there's some validity to evgeny's comment, based on my experience. But then again aromatics can be tricksy hobbitses on NMR.
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