[az_0k]

ok here is what happened. i synthesized some meso-stilbene dibromide from trans-stibene. i did an H1-NMR spectra on the meso-stibene dibromide using CDCL3 as my solvent and TMS as my reference. now here is what happened, i got a singlet at around 5.5ppm. could anyone please tell me what that peak represents? i just can't figure it out since i don't even have any double bonds here. any help would be greatly appreciated. thx a lot.

[impulse29]

Seems like you need help in two places. The chemistry I can't help you with, but learning how to post on forums, the Forum Rules and Policy can help. This would also explain the lack of replies.
- Impulse

[az_0k]

sorry, the title is changed now

[enahs]

I would guess based on the provided information you still had some unreacted trans-stilbene in your mixture.

[Mitch]

Can you post the spectra?

[az_0k]

no problem. the question is, trans-stilbene doesn't have a peak around 5, weird.
the spectra is on the last page.

[Albert]

The peak at 5.50 is due to the two methines. In the pdf you attached, there is the spectrum of trans-stilbene, not trans-stilbene dibromide.

And that makes a difference. 

[yamingx]

I can not download the PDF file, but the peak at about 5.5 ppm should be water peak which is from your solvent or samples according my experience.

[movies]

I can not download the PDF file, but the peak at about 5.5 ppm should be water peak which is from your solvent or samples according my experience.

The location of the water peak depends on what solvent you are using.  In this case, the spectrum is in CDCl₃ and the water peak would show up at about 1.56 ppm. 

In more polar solvents like CD₃OD, the water peak appears further downfield at 4.87 ppm, but in less polar solvents, like C₆D₆ then the water peak is shifted upfield to 0.40 ppm.

[yamingx]

The location of the water peak depends on what solvent you are using.  In this case, the spectrum is in CDCl₃ and the water peak would show up at about 1.56 ppm. 

In more polar solvents like CD₃OD, the water peak appears further downfield at 4.87 ppm, but in less polar solvents, like C₆D₆ then the water peak is shifted upfield to 0.40 ppm.

It is right what you said, but if the solution contain more water another water peak at about 5 ppm (depend on the amount of water in the solution will appear.

[movies]

You mean an actual H₂O peak instead of HOD?  You would need a ton of water to see that.  I've certainly never encountered it before, but my NMR book says that bulk water (e.g., undissolved droplets) will show up at about 4.7 ppm in CDCl₃.  If you have that much water in your sample, you have other problems!

[yamingx]

You mean an actual H₂O peak instead of HOD?  You would need a ton of water to see that.  I've certainly never encountered it before, but my NMR book says that bulk water (e.g., undissolved droplets) will show up at about 4.7 ppm in CDCl₃.  If you have that much water in your sample, you have other problems!

yes, the H2O peak. I am not sure if it exist as droplets, but generally the solution is clear. The chemical shift of H2O may shift a little, which is affected by the solvents, the property of solute and the concentration of solute and water. For an experienced chemist, when a strange NMR peak appear, the solvent residue should be considered firstly. 

[Custos]

The second NMR in the pdf file shows meso-stilbene dibromide. The peak at 5.5 is due to the two methine protons. There's also some junk around 1.3 which is almost certainly the water peak, as movies suggested. Here is the predicted chemical shifts from ChemDraw (pretty cool).