NMR question

[Sapps]

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I've been looking at this NMR and the only molecule I can come up with is kind of fuggly: Isopropenyl acetate -- an ester with one methyl group on one side and and ethene on the other side with a single methly group nearest to the ester on the double bond, for those that might not know the nomenclature.The NMR is Singlet at 6ppm(1H),singlet at 5.5 ppm(1H), singlet at 3.8ppm(3H), singlet at 2ppm(3H).

Formula is C5H8O2. That's the only thing I can come up with for it. I have to assume that for some reason the complex splitting isn't being shown to me. Any ideas?

 

[Sapps]

Actually, I think my proposed molecule works nicely. It just looks strange for some reason. Shrug.

 

[Sapps]

Right? heh.

 

[willthatsall]

Yeah, that's gotta be it.

 

[BisMuOxo]

NMR spectra always show splitting, your molecule is methyl methacrylate

CH2=C(CH3)-C(=O)-O-CH3

(There should be no splitting pattern here)

 

[willthatsall]

But how are those methyl protons adjacent to the ester oxygen only at 2.0?
I don't see how that is a better answer than:

CH2=C(CH3)-O-C(=O)-CH3

Where is the splitting in this molecule?

 

[Sapps]

This worthless correlation sheet doesn't show what the range is for a methyl group coming off a double bond. Hrmm.

 

[Sapps]

But how are those methyl protons adjacent to the ester oxygen only at 2.0?
I don't see how that is a better answer than:

CH2=C(CH3)-O-C(=O)-CH3

Where is the splitting in this molecule?

I think he/she is assuming the 2.0PPM singlet is CH3 off the double bond.

 

[willthatsall]

Yeah, I wasn't paying enough attention. Upon second review, I agree with what he/she said. There shouldn't be splitting either way, but it makes more sense the other way. Methyl group coming of a DB is usually 1.7, but 2.0 is probably it. Because if it is what you originally thought, you would have to say that the 3.8 peak is due to a methyl coming off a DB and 2 atoms away from the ester oxygen. That probably wouldn't be at 3.8. Also, the other compound looks better/more stable with the conjugated pi bonds.