[Plumbum]

Hey guys

I'm having major problems with this H NMR which u am supposed to analyze.

First thing I don't understand is that as far as I am concerned the numbers circled in green are supposed to tell me the total number of hydrogens. So the molecule should have according the spectrum 11 hydrogens but the molecular formular sais H8?? I am so confused can anybody please help ?

( easy language please I am not so good in NMR )

Thank u so much

[discodermolide]

Well the signal at 7.24 would seem to be chloroform.
Note that the molecule is symmetrical, which simplifies the spectrum. So you do actually have 8 protons here.
See if you can work it out from there.

[Plumbum]

Thanks for your answer:)

How do you known that the signal in 7.24 in chloroform? And it would be CDCl3 right ?

[Babcock_Hall]

It is a small amount of CHCl₃ in CDCl₃.  The isotopic substitution is never perfect, and this is a peak that is well known to users of NMR.  One of my students found a nice reference to the chemical shifts of various common solvents in common NMR solvents.  I can look it up if anyone is interested.

[Plumbum]

I'm am interested thank you

[Babcock_Hall]

NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities, J. Org. Chem. 1997, 62, 7512-7515
Hugo E. Gottlieb, Vadim Kotlyar, and Abraham Nudelman

[Plumbum]

I have a last question concerning signal number four. What does it mean for my interpretation when I have a doublet if a doublet? I know what that is but I really don't know how to analyze it, like how do I find out the number if hydrogens now under these circumstances :s??

Thank youu!!

[Plumbum]

Anybody ? I would be able to do the rest

[k1mng]

Higher order splitting like that which we see with a doublet of doublets represent the further splitting of a proton's signal by a (weaker than the first) coupling with another proton or other multiple protons.

So .. stronger couplings have larger coupling constants, which gives larger splittings, whereas weaker couplings have smaller coupling constants, which give the smaller splittings.

I hope that makes some sense and gives you some clues as to how to discern the 3 downfield signals

[Plumbum]

Okay but hat dies that mean for my interpretation ? How many neighbors do I have according the doublet of the doublet ?
Not quite sure yet

[Plumbum]

Help?

[Babcock_Hall]

If you just had a doublet, how many neighbors would you have?