Re: A simple question on 1H NMR water absorption peak

A thousand thanks, Lucas!

Sorry to make you confused.
The -0.88ppm is relative to the resonance, i.e. 0.88ppm below the
resonance, rather than the absolute chemical shift.

And you are definitely right the water peak is still downfield of TMS.

Great appreciation for all your helpful and smart remindness.

Best Regards,
Jing
lucasea@xxxxxxxxxxxxx wrote:
"Jing" <sjsongjing@xxxxxxxxx> wrote in message
news:1161575321.541614.166950@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
HI, all,
a simple question why the water peak of 1D 1H NMR is negative, -0.88?

Since
1. the larger the chemical shift, the more deshielded the proton.
2. electron pair of O-H bond is closer to oxegen, so the proton should
be more deshielded compared to the proton of TMS,
the water peak should be positive.

Then why it is negative?

What solvent? The furthest upfield water shift I can think of right now is
in C6D6, which is still ca. 0.5 ppm downfield of TMS. Could this be a
hydroxide, from deprotonation of water by some base?

If you're observing a broad peak at -0.88 ppm, it could also be a very
downfield shifted -OH, like a carboxylic acid, and it may be folded in on
the other end of the spectrum if you have your sweep width set too narrow.
Check this by, say, doubling your sweep width, and see if it's still in the
same place. On the other hand, it could be something unusual, like a M-Me
(M = electropositive metal like Al, Zr, etc.) or a M-H (again, where M =
electropositive metal.)

Eric Lucas

.

Relevant Pages