tag:blogger.com,1999:blog-3300702123878659843.post8191009218195381040..comments2024-03-26T05:25:50.831-04:00Comments on University of Ottawa NMR Facility Blog: Protic Samples in Aprotic SolventsGlenn Faceyhttp://www.blogger.com/profile/05146575170575279335noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-3300702123878659843.post-63592445572259375782012-05-22T07:16:34.687-04:002012-05-22T07:16:34.687-04:00:) Nice to see an example of this! I've spent ...:) Nice to see an example of this! I've spent many an hour trying to get a nice 'textbook' spectrum of some simple compounds for our teaching labs.<br />To get a nice looking spectrum with decent lineshape and couplings of the protic samples sometimes required tipping the tube upside down, shaking the sample out and then re-diluting the drop that remained...<br /><br />And then there are those that question their result based on a comparision to a reference spectrum run on a 100Mhz; prepared at a high concentration.<br /><br />Also the spectra can be dependent on amount of water present in the samples. I was asked to run methanol in CDCl3, and to get the CH3 to OH coupling required drying the solvent, methanol and the NMR tube.<br /><br />It just goes to show the laws of physics ensures the instrument always gives a correct result, but sometimes the chemist has to shift their perspective to see it!Duncanhttps://www.blogger.com/profile/00428207637407403652noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-53275823451265208882012-03-19T14:30:40.182-04:002012-03-19T14:30:40.182-04:00Glenn,
Further to my previous comment, I ran the...Glenn,<br /><br />Further to my previous comment, I ran the 1H NMR spectrum of dilute methanol in benzene-d6. The chemical shift of the -OH quartet was about 1.74 ppm lower than shown in the figure of the BLOG post (dilute methanol in acetone-d6). Some of this effect may be due to the ring current effects of benzene and it may be a better idea to run it in a solvent like dry CD2Cl2 but I suspect that at least some of the shift is due to the fact that the -OH protons are not hydrogen bonded to the solvent.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-85921470087506393412012-03-19T14:27:55.116-04:002012-03-19T14:27:55.116-04:00The OH proton chemical shift for dilute MeOH in ch...The OH proton chemical shift for dilute MeOH in chloroform is only 1.1 ppm. I guess I expected stronger H-bonding to acetone than to another methanol.Glenn Pennernoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-9515644413690285562012-03-19T11:20:17.691-04:002012-03-19T11:20:17.691-04:00Glenn,
Maybe there is a high frequency shift of t...Glenn,<br /><br />Maybe there is a high frequency shift of the -OH proton of methanol due to the hydrogen bonding to acetone. It would be interesting to observe the -OH resonance of methanol in benzene-d6 where one would expect no hydrogen bonding. Perhaps the shift is much lower than it is in acetone-d6.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-42118938523815451902012-03-19T09:11:35.692-04:002012-03-19T09:11:35.692-04:00Glenn,
What I do not understand is why there is n...Glenn,<br /> What I do not understand is why there is no high frequency shift due to hydrogen bonding of the methanol to the carbonyl oxygen of the acetone. <br /><br />GlennGlenn Penner, University of Guelphnoreply@blogger.com