[Machuu]

Hi,
I have a problem with interpretation of Lactulose 1H NMR spectrum. Lactulose has 14 protons (excluding OH groups). And my question is what is the location of signals from these protons in the spectrum? The doctoral student said that the signals have location about 3,80 - 5,80 ppm, but I can't find any publication to prove it. I need a signal location from a known number of protons to make integration the rest of the molecule.


Thanks for help.

[Mitch]

It looks like you have more than lactulose in that spectrum. I suggest you use a prediction software program for sugar NMRs, or you will be struggling for a while to decide which proton gets shifted in which direction.

This online prediction program gave the simulated NMR attached below:
https://www.nmrdb.org/new_predictor/index.shtml?v=v2.103.0

[Machuu]

To put it precisely it's lactulose modified by esterification. That kind of molecule was synthesized for the first time, so i must find singals from known protons e.g those coming directly from lactulose (14)

[Mitch]

Did you try entering your molecule in the simulator? It will show you which protons generate which signals.

[Machuu]

Yes I did, the signals have similar range. Thanks for help.
But now I have another question.

The solvent was CDCl3 so the signals must come from another compound. Do you have any suggestions?

[Mitch]

Sorry, it's been over a decade since I ran an NMR. Hopefully, one of the spectroscopy gurus can answer.

Please also see this paper:
NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities
J. Org. Chem., 1997, 62 (21), pp 7512–7515
DOI: 10.1021/jo971176v

[clarkstill]

This paper is an updated version of the one Mitch provided, in case your impurities aren't listed:

NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist
Organometallics, 2010, 29 (9), pp 2176–2179
DOI: 10.1021/om100106e

To me, the peak at ~3.7 looks a lot like THF - is there another signal with the same integral at 1.85ppm? I don't really recognise the singlet at 2.8. What were the conditions for the reaction you conducted and the purification that followed?

Regarding the spectrum of your compound itself - can you run some 2D techniques on your molecule? TOCSY might be particularly useful as it should separate out the two sugars.

[Babcock_Hall]

There is a large body of NMR data on oligosaccharides, but I am sorry that I don't have a reference handy.

[wildfyr]

That's THF

[wildfyr]

I have to say, that this is an NMR of a big ol' pile of garbage. Thats OK, we all make plenty of such piles, but its so messy that there isn't much information here. Its just a bunch of oligomeric crap. Try running the reaction again more carefully (and again, and again) until you have better resolved peaks.

Here is an NMR of lactulose http://www.hmdb.ca/spectra/nmr_one_d/5170. Its not pretty, but you can still see where things are better resolved.

P.S. I found that by typing in "lactulose NMR" into google and clicking the very first link.

[clarkstill]

Didn’t OP say it was (meant to be) an ester of lactulose?

[wildfyr]

I still thing it looks very sloppy. The ester protons should give a bunch of nice singlets.. If it's acetylated they will be on 3H

[clarkstill]

Agreed, there are definitely multiple things in there, I was just clarifying that you wouldn't expect it to match literature spectra of lactulose itself.

[Babcock_Hall]

@OP, There are many -CHOH groups in a typical polysaccharide.  What do you think will happen to the chemical shift of this proton if the oxygen becomes acetylated?