tag:blogger.com,1999:blog-3300702123878659843.post8561579735926047083..comments2024-03-26T05:25:50.831-04:00Comments on University of Ottawa NMR Facility Blog: The NMR Time ScaleGlenn Faceyhttp://www.blogger.com/profile/05146575170575279335noreply@blogger.comBlogger18125tag:blogger.com,1999:blog-3300702123878659843.post-87559036572651678012020-03-09T14:57:57.871-04:002020-03-09T14:57:57.871-04:00Anonymous,
The answer lies in the lifetimes of the...Anonymous,<br />The answer lies in the lifetimes of the states compared to the duration of the FID and the frequency difference between the states. When an exchange event occurs during the measurement, the frequency changes in the FID. The best explanation for this is given in James Keeler's book "Understanding NMR spectroscopy" second edition pp. 286 - 293.<br /><br />Glenn Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-41373821535092694372020-03-07T11:54:54.668-05:002020-03-07T11:54:54.668-05:00Thanks for clearing that out! I guess what I mean ...Thanks for clearing that out! I guess what I mean to ask is, why is it related to the frequency difference between the peaks? Why isn't it possible to measure/ resolve states when the system alternates faster than this?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-91882439627566727492020-03-06T11:21:39.175-05:002020-03-06T11:21:39.175-05:00Anonymous,
The NMR time scale is "related&quo...Anonymous,<br />The NMR time scale is "related" to the field strength only in that the strength of the field affects the frequency difference between peaks. The NMR time scale is NOT equal to the reciprocal of the proton resonance frequency. I'm not sure what you mean by the question "How do you relate these timescales to the actual NMR measurement?"<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-31576685533287332552020-03-06T05:21:05.953-05:002020-03-06T05:21:05.953-05:00Dear Glenn,
In my NMR course it is stated that the...Dear Glenn,<br />In my NMR course it is stated that the NMR timescale relates to the reciproke of the frequency of the spectrometer. I.e. for a 250 MHz spectrometer this would be 4 ns. So it is stated that rotation must be faster than this to result in equivalence. I was confused by this since later coalescence of OH protons is explained by fast proton exchange. But I had a hard time believing that this exchange occurs on nanosecond timescales, though I don't know for sure. Here a different statement is made, ie the relevant factor is the difference between the peaks of the alternate states, which brings it to timescales in the micro/-millisec regime. Is what I've learned than flat out wrong? <br /><br />And second question:<br />How do you relate these timescales to the actual NMR measurement? <br /><br />Thanks in advance!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-18061746256347509292013-06-18T08:35:29.558-04:002013-06-18T08:35:29.558-04:00Anonymous,
7Li is quadrupolar and the line width ...Anonymous,<br /><br />7Li is quadrupolar and the line width may be broadened due to fast relaxation in addition to any effects due to exchange. As a result, I don't think you can extract an exchange rate directly from the width of the signal.<br /><br />Glenn Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-85312363134857547282013-06-13T07:52:00.120-04:002013-06-13T07:52:00.120-04:00Dear Glen,
Say, the 7Li NMR spectra has FWHM of ...Dear Glen,<br /> Say, the 7Li NMR spectra has FWHM of 10kHz. can I estimate jump rate from spectral width ? if yes, can you explain me how ?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-43258350161557977742012-02-03T09:16:07.755-05:002012-02-03T09:16:07.755-05:00Anonymous,
When there is no interconversion the c...Anonymous,<br /><br />When there is no interconversion the concept of an NMR time scale as described in this post has no real meaning except that the conversion is infinitely slow on the NMR time scale.Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-12536484894393308412012-02-03T09:11:16.837-05:002012-02-03T09:11:16.837-05:00Anonymous,
When one refers to a time scale relati...Anonymous,<br /><br />When one refers to a time scale relative to the inverse of the Larmor frequency, one is usually talking about relaxation processes as T1 and T2 depend on spectral density functions which have minima close to the reciprocal of the product of the Larmor frequency and a motional correlation time.Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-74236985815495589312012-01-26T11:02:51.503-05:002012-01-26T11:02:51.503-05:00To follow up on what I asked before, I want to cla...To follow up on what I asked before, I want to clarify that I was asking what the NMR time scale is if there is no interconversion. <br /><br />Sorry for the confusionAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-6977291323390507252012-01-26T10:49:07.938-05:002012-01-26T10:49:07.938-05:00Thanks for this post.
There are still some things...Thanks for this post.<br /><br />There are still some things that are unclear to me.<br /><br />What is the time scale if you see only a single peak (say in metal)?<br /><br />I have people refer to the timescale being the inverse of the larmor frequency. Is that true?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-17994159629829432202010-04-15T04:40:39.972-04:002010-04-15T04:40:39.972-04:00Dear Habibur
thank you for your comment.Dear Habibur<br /><br />thank you for your comment.Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-36762331766723687592010-04-15T01:36:07.422-04:002010-04-15T01:36:07.422-04:00Dear Glenn,
The problem with anonymous on March 5,...Dear Glenn,<br />The problem with anonymous on March 5, 2010 is that he/she probably did not understand why we see a single peak in an exchange situation. The single peak represents neither of the conformations A and B, rather it is an weighted average of the resonance frequencies of the two (this should be clear from the figure shown). Actually a nuclei attached to any anisotropic molecule feels different extent of the applied magnetic field at different orientations relative to the field direction and hence resonate at different frequencies. In the liquid (and gaseous) state where the rate of tumbling of the the molecule is very high (of the order of THz) we see a single sharp line, which represent an average resonance frequency from all possible orientations.<br />M. Habibur RahmanUnknownhttps://www.blogger.com/profile/00822895070376393873noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-34192088585813737472010-03-08T10:40:29.466-05:002010-03-08T10:40:29.466-05:00Dear Anonymous,
No you cannot say that the jump r...Dear Anonymous,<br /><br />No you cannot say that the jump rate is 20 times per second. You can however say that it is much slower than 20 times per second. You can however get an estimate of the jump rate at the coalescence temperature.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-20803159936210569342010-03-06T07:48:54.511-05:002010-03-06T07:48:54.511-05:00Dear Facey,
Lets say there are 2 peaks for one car...Dear Facey,<br />Lets say there are 2 peaks for one carbon because it goes some reorientataion and the difference between these 2 peaks is 20Hz. Can we say it jumps one from to another structure 20 times per second? If say "yes", I want to ask this where the problem begins:<br /><br />if it is fast enough we probably observe one peak so we say that intercoversion is fast compared to NMR time scale so we observe one peak. Then it is meaningles to say "yes" for my first statement because there will be no seperation for the second case even it changes its structure more faster than 20Hz....<br /><br /><br />ozguralver@anadolu.edu.trAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-14212313553212151172010-03-05T08:42:08.788-05:002010-03-05T08:42:08.788-05:00Anonymous,
It is whether or not the frequency dif...Anonymous,<br /><br />It is whether or not the frequency difference between the reonances is comparable to the frequency of interconversion between A and B.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-6030902393592597682010-03-05T08:22:05.668-05:002010-03-05T08:22:05.668-05:00Still I did not understand.In general it is okey. ...Still I did not understand.In general it is okey. Which parameter indicates the the NMR time scale? AQ:Aacquisition time, pulse duration (P1) or what??<br />please help...<br />ozguralver@anadolu.edu.trAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-23213757431518161942009-06-08T19:09:48.770-04:002009-06-08T19:09:48.770-04:00I have an examination in NMR spectroscopy tomorrow...I have an examination in NMR spectroscopy tomorrow. Your explanation was very useful and clarified the meaning of the term 'NMR time scale'! I'm so greatful!!!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-91161588264857393302009-04-20T22:07:00.000-04:002009-04-20T22:07:00.000-04:00Thanks! You cleared that up for meThanks! You cleared that up for meAnonymousnoreply@blogger.com