[miss_molecule]

Oh no 

I just saw that the OH can't be splitting the complex signal, because the expansion is treated with D2O. Then I seriously don't understand anything about this signal...  and I am running out of time 

[Squirmy]

I agree it doesn't look like the "multiplet" is being split by the OH. Was the sample only treated with D2O for the expansion? If so, that might explain why you see a doublet for the OH in the normal spectrum, but no corresponding splitting in the expansion.

Maybe D2O was added to the expansion so that you didn't have the extra, even more complicating splitting. I wouldn't call it a multiplet as is, but I might with that extra level of splitting.

Could you assign the splitting pattern for the"multiplet" (like "dd")? What is it split by? Hint there are three types of N_v.

[miss_molecule]

Only the expansion is treated with D2O.

For me, the "multiplet" looks like dqd. it its split by the three hydrogens on the methyl, and the two on the methylene. I can't see anything else able to split it, when OH is removed?? So what is the third Nv? Or does the two hydrogens on methylene count as two different Nv's? I would still expect an "sixlet" though...

[Squirmy]

Yes, the two hydrogens of the methylene are different N_v's. If the OH were also causing splitting it would be a ddqd. 2 doublets for the methylene, a quartet for the methyl, and another doublet for the OH, not necessarily in that order. This was what my earlier yikes was about.

With D₂O for the expansion, it simplifies to a ddq, which is still complicated but J-values can be determined.

[miss_molecule]

Thanks a lot.

I'm going home now, have to think more about this later tonight It is way to complicated for me! I will try to calcualte the J-values, and see if it makes more sense.


But what about the other coupling constants? none are the same, except those for the doublet of doublets... Can that be right?? (see table)

[Squirmy]

a slight correction to my last post...a dqd would be more correct than ddq for the "multiplet"

As for J-values, you should have one for each type of adjacent hydrogent. E.g. for a dd, there should be 2 J-values. For a dqd, there should be 3 J-values.

You should see J-values match up, though. That is, if the CH₃ is split into a doublet by CH-O and has a J-value of X Hertz, the CH-O is split into a quartet by CH₃ with a J-value of X Hertz.

[Squirmy]

I came up with the blue/red image several posts ago, b/c I recognized it as a dqd. If you have a dqd, there are a max of 2x4x2 (16) peaks. In your case, a couple of those peaks are overlapping.

Can you see the two quartets in the picture? (I'll post it again)

[miss_molecule]

I see what you mean, and the J- values fits perfectly! 

So the coupling tree for the dqd would look like this? (se picture)

But what about the coupling trees for the methylene hydrogens?

I just want to say thank you sooooo much! This page is amazing! I love that you don't just post the answear, but make me think instead. In a few year I will in fact be a chemistry teacher myself  But not at this level, haha 

[Squirmy]

There ya go! Very nicely done!!

Have you tried the methylene splitting since I mentioned a dd should have 2 J-values? The table above shows only one J-value for each.


Good luck with the teaching!  That's great to hear, b/c we need more good HS chemistry teachers!!