# Most negative and most positive value for proton chemical shifts

What are the most negative and the most positive values for proton chemical shifts recorded till present?

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I suspect the most positive values can be found in superacidic media such as $\ce{HF - SbF5}$, which contain extremely poorly solvated, essentially bare $\ce{H^+}$ ions. – Nicolau Saker Neto Aug 22 '14 at 14:08
What are the values? – Marko Aug 22 '14 at 15:28

## 1 Answer

I don't know if the following two examples present the "largest" upfield and downfield proton-nmr chemical shifts, but I suspect they're in the running. The dihydropyrene dianion example has 16 pi electrons

delocalized around the periphery of the pyrene frame. It fits the 4n rule with n=4, so it is antiaromatic. The [16]-annulene dianion has 18 pi electrons and fits the 4n+2 rule with n=4, so it is aromatic. Note how the direction of the ring current reverses between antiaromatic (paramagnetic current) and aromatic (diamagnetic current) systems. More intesting proton chemical shifts can be found in this compilation.

Edit

Guilty of thinking organic. If we're including inorganic proton shifts, then how about IrHCl2(PMe(t-Bu)2)2 which has a chemical shift of -50.5!

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Thanks. I examined the link you posted. I see the rhodium-pentacyano-hydride has around -10 ppm and that theoretically, a naked proton would have a chemical shift of 40 ppm (which is probably the maximum possible). So I will take the most negative shift to be -10 ppm, and the most positive "measured" to be 21.24 ppm. If anyone finds some even more extreme values, I would like to see them. – Marko Aug 22 '14 at 19:51