Talk:Chemical shift

Untitled
the definition of chemical shift was invented to give standard differences in frequencies for different molecules, independently of operating magnetic field. I've come accross the following definition: sigma = (delta - delta_ref)x10^6/delta_ref where "sigma" is the chemical shift "delta" resonance frequency of the molecule of interest "delta_ref" chemical shift of TMS (tetramethylsilane) the result is in ppm as well and does not refer to field strength (or indirectly to frequency) of a magnet. Please take a look at Carlson Centre for Imaging Science covering this topic. (this is my first post to wikipedia) --Witoldmatysiak 20:47, 20 Jun 2005 (UTC)

Hello, That's kind of true: What you've found is the correct definition of a chemical shift (using different letters), see also IUPAC, 2001. The author of the article means the same thing, I would say, and didn't want the equation look to difficult (which, in principle, is a very good thing). Please note that your definition is still dependend on the strength (actually, flux density) of the external magnetic field, because that's what gives you the reference frequency! The chemical shift is indeed usually called &delta;, but that does of course not change the physics behind it... Maybe I find some time to add a bit to the text some time. Kindest regards, Ksei 04:06, 26 July 2005 (UTC)

Magnetic properties of most common nuclei
This chart kind of bothers me. Not because the information presented is inaccurate, but rather that it shows a lot of unexplained information about the different nuclei. If you're going to show the spin number, the magnetic moment, the electric quadrupole moment and so on, don't you think it would be good to explain how these are important? Like for 14N, the electric quadrupole creates such broad signals as to be useless for structure determination compared to 15N? In a lot of ways, this seems like information that belongs in a separate article from chemical shift since for many of these nuclei the typical chemical shift definition using TMS does not apply. Perhaps a separate article from the main article on other NMR nuclei besides proton and 13C NMR would be a more appropriate place to talk about these different nuclei. Otherwise, an addition to the current article about NMR in general would also be useful, but I think as it stands this is somewhat irrelevant to the idea of chemical shift. --Ghiles 23:18, 13 May 2006

Chart doesn't belong here. Should be in magnetic resonance--Biophysik (talk) 00:40, 8 December 2008 (UTC)

Such language!
The magnetic field of a NMR magnet is static, so what is its operating frequency? What are some units like tesla and gauss? If the nucleus you are observing is Si, isn't that the most important one? — Preceding unsigned comment added by 24.131.7.107 (talk)

Your first two questions are answered in the NMR Spectroscopy wiki page. I'm not quite sure what your concern is in the third...what and where is the specific wording that you're talking about? DMacks 04:11, 12 September 2006 (UTC)

The fastest way to..
This section, while perhaps made with good intentions, seems quite out of place on wikipedia. Is wikipedia a textbook for everything? No, I'd say not. Perhaps links to exercises could be placed in the external links, instead of in a part of the article? Shandolad 10:29, 15 October 2006 (UTC)

Chemical shift anisotropy
Chemical shift anisotropy is mentioned in Magic angle spinning. Is redirection of chemical shift anisotropy to this article OK? Could this phrase be worked into this article, e.g. where anisotropic effects are mentioned in Chemical_shift?

GilesW 22:07, 6 October 2007 (UTC)

Other shift effects
Leaving here my revised version of this section which was rather hastily reverted, despite the fact that it corrected mistakes and irrelevancies in the original while adding new (relevant) material... -

Other shift effects
Other phenomena that shift NMR frequencies are the Knight shift, which occurs in metals, and the paramagnetic shift associated with systems containing unpaired electrons.

Chemical shift is also used to refer to differences in spectroscopic frequency due to local chemical environment in Mössbauer and X-ray photoelectron spectroscopies.

-- Pdch (talk) 22:39, 16 November 2007 (UTC)

Dimensions??
The big equation at the end of the section "Operating frequency" fails dimensional analysis, because in the middle section the units are omitted. I can see how this style makes writing the formula easier, however it should be restricted to back-of-envelope calculations and not proliferated in an important media like Wikipedia. Units are not an insignificant appendix but an integral part of a quantity, and omitting them makes a formula at least ambigous if not plainly wrong. I suggest

\omega _0 = \gamma B_0  = \frac \times 1\,{\rm{T}} = 42.5\,{\rm{MHz}} \,$$ If consensus is reached please somebody put it in.

There is also a problem with the formula of the gyromagnetic ratio just before: µ is used in the formula as the *relative* magnetic moment (relative to the magneton) whereas in the text it is called magnetic moment. This is confusing to the layman. 213.68.42.99 (talk) 08:24, 4 May 2009 (UTC)


 * Makes sense! I have made the change in the text, thanks for the comment V8rik (talk) 17:22, 7 May 2009 (UTC)

omega or f ??
I find 3rd (big) equation somewhat confusing. Usually omega is used for "circular velocity" measured in rad/sec, while frequency is measured in 1/sec=Hz. So omega=2*pi*f. Thus in 3rd equation omega should be probably changed for f, or the same equation can be written for omega but using Plank constant hbar instead of h. Thanks, Evgeny. —Preceding unsigned comment added by 143.167.7.127 (talk) 15:19, 27 February 2011 (UTC)

J-coupling
I suggest mentioning j-coupling and the associated multiplets in this article. The J-coupling article needs to be clarified in that respect and linked in to this article. GilesW (talk) 18:50, 27 June 2011 (UTC)

Definition rewrite
Hi Smokefoot, your recent edit was more than a English language tidying (see edit summary), it also involved a definition rewrite. Nothing wrong with that of course but I think we should discuss definitions. The new definition in my view is not an improvement and also unreferenced? V8rik (talk) 17:46, 15 October 2011 (UTC)
 * Thanks for noticing. Yes, I thought that the former definition was too complicated.  A chemical shift is just a frequency (relative to some standard - maybe we should mention the standard).   You are welcome to "re-tidy" if you have a clearer way of explaining it.  A more rigorous physics-based definition would be difficult for most readers (and I) to understand.  IUPAC's definition for XPS chemical shift is at http://goldbook.iupac.org/C01037.html. --Smokefoot (talk) 18:14, 15 October 2011 (UTC)

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Analytical chemistry
Urdu 37.111.137.144 (talk) 04:33, 19 November 2021 (UTC)

Missing minus sign
The first equation should have a minus sign. This is important for things like 15N and also for dynamic nuclear polarization. Unless people object, I would update the math to have that minus in the right place. MonsterBrain (talk) 12:04, 3 December 2023 (UTC)


 * No objections having been received, I am making the edit. MonsterBrain (talk) 13:04, 4 December 2023 (UTC)

Dead link
Someone care to update source? https://web.archive.org/web/20110926141002/http://nmrcentral.com/2011/08/chemical-shift/ Xikron (talk) 18:35, 16 February 2024 (UTC)