Talk:Nuclear magnetic resonance

whoo ... big edit.

I divided the page into sections, and greatly expanded the description of how NMR works. This is the closest I have ever come to giving a quantum mechanics lecture! Please help with any parts that are unclear...

The history section needs better organization, although I'm grateful for whoever put that up there. More discussion of various techniques (FID, spin-echo, CPMG) is necessary, as is discussion of the various factors that are measured by NMR spectroscopy. --hb, 18 Nov 2002

Contents

1 sections need to be removed. 2 Magnetic or electromagnetic? 3 Nuclear spins do not emit radio waves 4 Cosy section 5 How NMR Works - major edit 6 Splitting the NMR page in two- NMR and NMR spectroscopy 6.1 Good idea 6.2 Splitting up & Solid-state NMR 7 Fullerene NMR 8 needed

sections need to be removed.

The description of the NMR signal as reading the radiation that comes out when the nuclei reequilibrate needs to be removed. This is a common misconception about what the NMR signal is. Both T2 and T2* measurements are made while the nuclei are in disequilibrium; although the bulk magnetization decreases, it is because the signals are going out of phase with each other (because they are resonating at different frequencies), not because the nuclei are reequilibrating. (anonymous, 18 Feb 2004)

To me, the text seems to be correct, although it might lead to some confusion that T2 (dephasing) is discussed directly after the re-equilibration, which would refer to T1 (population relaxation). I tried to clarify the text (then saw that I mixed up T2 and T2*) - Hankwang 21:53, 18 Feb 2004 (UTC)

I would rewrite the section completely in terms of commonly used names for T1 and T2 - (it can be either longitudinal and transversal or spin-lattice and spin-spin relaxation). It's odd to mix up T1 and T2 together because generally the processes of spin-lattice and spin-spin relaxation are independent both in classical terms (Bloch equations) or in QM therms (Redfield theory, etc). Moreover, the difference between T1 and T2 may be several orders of magnitude ( when speaking about solid-state NMR). Generally, the T2 can not be dependent on T1, especially in such a strange manner like placed in the formula in the bottom of this section. What is the source of such an odd relation between T1 and T2 ?? MakVal

In order for the spins to relax fully, they must also stop precessing in unison. That is the link between the two. --Pdbailey 00:08, 10 May 2005 (UTC)

Magnetic or electromagnetic?

Concerning the sentence: "When radio power is sent to the antenna, it generates an oscillating magnetic field H1 (not to be confused with the external magnetic field). "

should this not be "..generates an oscillating electromagnetic field"? Foppe Brolsma, brolsma_produkties (at) hotmail.com

No, the current text is correct. To call it an oscillating electromagnetic field would imply it were electromagnetic radiation, which it isn't. -- Tim Starling 00:45, Mar 19, 2004 (UTC)

The fact that it is a radio antenna which generates the field implies that it is electromagnetic radiation. Moreover, the text mentions left-handed and right-handed circularly-polarized photons, which also implies it is radiation. What you might mean is that

1. we are dealing with the near field (i.e. less than a wavelength from the radiation source), which means that E and B are not necessarily perpendicular. However, NMR would work just as well in the far field (e.g. at higher radio frequencies that have a shorter wavelength) so that is not the issue here.

2. It is the magnetic component that interacts with the nuclei. However, in the description of quantum-mechanical transitions in atoms in an electromagnetic field, it is mainly the electrical component that acts on the atoms, but that is not a reason to call it "transitions involving an oscillating electric field" instead of "radiative transitions".

Yeah OK, that could be right, sorry. When I was taught this initially, we used the semi-classical treatment which talks entirely in terms of a rotating or oscillating magnetic field. Chapter 3 of this random web site (http://www.cis.rit.edu/htbooks/nmr/inside.htm), which I found using this google search (http://www.google.com/search?hl=en&ie=utf-8&oe=utf-8&q=nuclear+magnetic+resonance), uses terminology very similar to what I'm used to:

A coil of wire placed around the X axis will provide a magnetic field along the X axis when a direct current is passed through the coil. An alternating current will produce a magnetic field which alternates in direction.

In a frame of reference rotating about the Z axis at a frequency equal to that of the alternating current, the magnetic field along the X' axis will be constant, just as in the direct current case in the laboratory frame.

This is the same as moving the coil about the rotating frame coordinate system at the Larmor Frequency. In magnetic resonance, the magnetic field created by the coil passing an alternating current at the Larmor frequency is called the B1 magnetic field. When the alternating current through the coil is turned on and off, it creates a pulsed B1 magnetic field along the X' axis.

I'm happy to go with common usage, whatever that may be. Do you have any references calling it an electromagnetic field? -- Tim Starling 15:08, Mar 19, 2004 (UTC)

Well, no, I was merely countering the statement that "it is NOT E-M radiation". :) I'd say the current article text is fine. I certainly would not agree with the moving-coil description above since a correct transformation to a rotating coordinate system would be much more involved than is suggested. The rotating-wave approximation which lies behind this is purely quantum-mechanical, and after this approximation, it turns out that you can describe the precession of the spins in a rotating frame as if there were no B0 field. However, I strongly oppose to "deriving" the approximation from a macroscopic and incorrect metaphor. -- Hankwang 16:52, 19 Mar 2004 (UTC)

Nuclear spins do not emit radio waves

Nuclear spins do not emit radio waves in response to a radio frequency pulse. This mistake has been repeated in so many text books that no doubt many people believe it. David Hoult, an impeccable physicist, made a valiant attempt to correct this misconception in 1989. The reference is: D. L. Hoult, Concepts in Magnetic Resonance, 1989, 1, 1-5. The wise reader will start here. -Jan Wooten

Wikipedia:Be bold in editing pages -- Tim Starling 06:25, May 16, 2004 (UTC)

Agreed. What was there was a poor O-chem understanding of the process. I fixed it up a little but left it looking like a first draft... come on wiki process! Pdbailey 05:23, 13 Nov 2004 (UTC)

Cosy section

The COSY section should be removed/sidelined until it can be explained better. It reads scattily, as if pulled directly from a textbook, and there are many technical aspects unexplained (double Fourier-transformation, Pulses, how the 2nd dimension arises) and many aspects are poorly written (Example of ethanone). I feel this doesn't make it an asset to this entry.

Any feeling/input on this would be appreciated because its a very major edit! Unless anyone objects I'll be removing it when I edit the theory of this section. (And hopefully have time to put something meaningful in its place). Let me know --Lee-Jon

How NMR Works - major edit

The How NMR Works section has been renamed to Theory... and consigned to the latter part of the article so not to frighten undergraduates etc. It has been expanded so (hopefully) every concept makes sense and has some theoretical background presented.

Sections I (or you!) want to add are on spin-spin coupling, Pulse NMR & Fourier-transformation, and possibly a brief talk on the nuclear Overhauser effect relevant to NMR. I think that covers almost everything to give some detail on NMR without it being too technical. --Lee-Jon 21:52, 9 Mar 2005 (UTC)

1. Nice addition! Thanks. Good work in my opinion. I took out the line between the Image tag and the first line of text--to accommodate "some" browsers.
2. We might experiment with controlling the size of the Progesterone plot, see code in edit view to produce the diagram to the right. [NB: IMAGE REMOVED] ---Rednblu | Talk 22:15, 9 Mar 2005 (UTC)

Thanks for praise. Yeah I agree with the image - it looks much nicer that way -i've amended it and taken the code out of the edit page. Although I feel the COSY section need much refinement, maybe even a major edit to make it a "2D NMR/Experimentation" section. Lee-Jon 21:12, 10 Mar 2005 (UTC)

Splitting the NMR page in two- NMR and NMR spectroscopy

I am an organic chemist and I would describe myself as an experienced user of NMR spectroscopy. I can not claim to be an NMR expert, I could never write my own pulse sequences etc. I also teach introductory organic chemistry, covering the basics of 1D proton and C-13 NMR in the first semester, then students get to run a COSY and a DEPT experiment in their second semester. I am therefore very familiar with explaining the basics of the NMR spectroscopy. It seems clear to me that there are two different topics covered on this page currently

1. Nuclear magnetic resonance- the physical phenomenon, and
2. NMR spectroscopy- the analytical technique.

For example MRI (as I understand it) uses the phenomenon of NMR, but is clearly distinct as a technique from NMR spectroscopy.

This difference between physical phenomenon and analytical method has already resulted in there being separate pages for Infrared and Infrared spectroscopy, also Ultraviolet and UV/VIS spectroscopy. See Category:Spectroscopy for other page titles.

NMR spectroscopy is the most widely-used technique in modern organic chemistry and it surely deserves its own page. The spectroscopy page should have less discussion on the theory and physics, and much more on how the technique can be used to analyse molecular structure- things like equivalence, chemical shift, integration, multiplicity, diastereotopic protons in chiral molecules, which nuclei lend themselves well to analysis and which don't, etc. Some of this information is already on this page, much is not. My undergraduate students would currently find almost nothing on this page of value to them. We need this separate NMR spectroscopy page. The COSY section could be part of this new page or could be big enough for its own page. What do others think? Walkerma 07:14, 14 May 2005 (UTC)

PS: I should mention that I have an ulterior motive- we are currently revamping the standard data table for chemical compounds, and we are including a link (for some compounds) chemical shift data or to scans of actual 1H and 13C spectra. The idea is that when you look up (say) limonene, you could click on a link to see NMR data or a spectrum. I would like to have the standard "explanation" link on these tables to lead to a spectroscopy page. Walkerma 07:21, 14 May 2005 (UTC)

Good idea

I agree, however NMR Spectroscopy extends far beyond Organic chemistry so maybe the page could be written from a few angles:

1. Sample preparation
2. organic structure (typical stuff)
3. biological structure (structure/function etc)
4. dynamic NMR (reactions/thermo etc)
5. Solid state NMR
6. multinuclear NMR (13C 15N 17O etc)
7. Techniques (multidimensional etc)
8. Fourier transformation and computational methods

Unlike UV/VIS and similar techniques, modern NMR Spectroscopy is a very large and very complex area. And as I'm sure you're aware, an end-user approach to NMR is very difficult to discuss without having to delve into some nuclear physics. Any section on NMR Spectroscopy should continually reference a theory section to keep it accurate.

The page has been created here and I'll try and finish a good first build throughout this month! Lee-Jon 09:11, 17 May 2005 (UTC)

Thanks for starting that- it's a nice job so far! Please can I encourage you to keep writing it at a very basic level. I know from teaching this, you only need a very basic understanding of the physics underlying it- just like you don't need to understand general relativity to understand that an apple falls to the ground. I would avoid getting into discussions of T1, T2 etc. on this page if possible. Also, can I recommend that this page be renamed as NMR spectroscopy (small s) (currently a redirect), this seems to be the more usual form when you look at [[Category:Spectroscopy. I agree that all of those topics need covering- these probably all warrant their own pages. Wikipedia is exploding in size and depth, it seems to me, and with the chemical compounds pages we probably have 500-1000 compounds covered, up from perhaps 100-200 a year ago- so having 10 pages on different aspects of NMR, written at various levels, is totally reasonable. I would suggest that 13C deserves its own page. One small point, should that be "heteronuclear" NMR for 15N etc? Multi to me implies many, which sounds like HETCOR, APT etc. Walkerma 16:53, 17 May 2005 (UTC)

Thanks for the comments. You're right, when I said multi I meant hetero. Typing faster than I'm thinking! Agreed about the small "s". I'll change that. Lee-Jon 09:08, 19 May 2005 (UTC)

Splitting up & Solid-state NMR

I am a bit torn apart in my feelings for splitting up the article on NMR and it's spectroscopic technique. From a scientist's point of view, I oppose this. However, for an Encyclopedia, it's important to be not only accurate and precise, but also brief. Therefore it might be good to proceed to disentangle the "physical phenomenon" and the "spectroscopy", setting the appropriate links. Aside of that, I suggest to write a separate article on solid-state NMR, which may be broken up into two sections describing the effect and the spectroscopy if you show this can be done successfully.

Fullerene NMR

In their 1985 experiment, R. Curl and R. Smalley of Rice University obtained mass spectrum of carbon clusters, where even numbers have large intensities and n=60 is particlularly so (Nature, 1985, 318, 162). They proposed the C60 structure as a soccer ball.

The NMR spectrum of buckminsterfullerene (C60) was published in 1990 by another Nobel prize winner Kroto, H.W. of University of Sussex (J. Chem. Soc., Chem. Commun. 1990, 1423). This confirmed the earlier proposed structure. Indeed, IR spectrum of C60 precedes NMR (Nature 1990, 347, 354). Together, IR and NMR spectra confirmed the structure of C60.

This entry need to be changed to reflect this fact.

needed

I think the article could use a nice diagram of the innards of an NMR machine and an explanation of how the larmor frequency relates to the naming of individual machines (field strength correlation etc.) though, I am not the one to do it. I can't find a good PD diagram of an NMR device so.....any takers?--Deglr6328 20:11, 18 Jun 2005 (UTC)