NMR doesn't match up with Molecule?

[rockyDoctora]

Methyl Benzoate:

According to Kaplan, this NMR spectrum is for methyl benzoate:

I dont understand this. From the structure of methyl benzoate, there should be four groups:

1) hydrogen at para (int = 1)
2) hydrogens a bit closer to ester on benzene ring (int = 2)
3) hydrogens again, a bit closer to the ester on benzene ring (int = 2)
4) hydrogens on the methyl group (int 3)

However, the number of peaks and the integration values on the NMR are 3, 3, 2... Is this right?

Thanks for you help!

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[mohad]

My ochem teacher said that sometimes the meta and para hydrogens can be considered "the same chemical environment" and therefore they're often grouped together as 3 hydrogens instead of 1 and 2. He also told us to not be surprised if we see that again on other sources. Really good NMR machines will distinguish them as 2 and 1, but they can be a group of 3.

Sorry, I meant para and meta. Not Ortho.

 

[rockyDoctora]

Sweeeeeet. Thanks a lot for the info!

 

[MD Odyssey]

Kaplan is completely wrong here - there is a lot more going on. The H-NMR spectrum from SDBS for methyl benzoate is this:

Edit: I suspect that the link to SDBS I posted was disallowed for some reason. If you go to SDBS and look it up, you'll find that there are additional signals that Kaplan hasn't showed you.

 

[collegestud2013]

http://imageshack.us/photo/my-images/684/capturemebenzoate.jpg/

That's the ChemDraw predicted 1H-NMR for Methyl Benzoate. So yes, there are three separate signals for the aromatic protons, but two of them are essentially so close they nearly merge into one signal.

 

[axo86]

lol @ singlets @ 7 and 8 ppm