How come this is 2 singlets ???

[atlanta213]

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This is from topscore 1.
Answer is B. but I think choice b has only 1 singlet. why not A???

 

[whoaaitzkyle]

This is from topscore 1.
Answer is B. but I think choice b has only 1 singlet. why not A???

Choice B has 2 singlets. You should look at the different hydrogens. The OCH3 is one set you can look at (since they are both identical it only splits once). Then look at the hydrogens on your benzene ring and you get another singlet that forms.

 

[condoleezarice]

Huh? Why would it only have one singlet? There are the protons on the CH3, then there are the protons on the aromatic ring. They each account for one singlet. So, there should be two singlets.

 

[chessxwizard]

The molecule has a plane of symmetry down the middle. Equivalent hydrogens do not split each other.

 

[yakuza]

You have a total of 10 H's but only 2 types

 

[admap]

The hydrogens should have doublets, because their neighbouring C has one H and it will be (n+1). What's up with that??.. my NMR is seriously challenged..
Also, wouldn't the acetone have 2 singlets as well?

 

[klpennin]

So, wouldnt A have a triplet and a quartet bc they are ethyl groups.

 

[atlanta213]

I guess b should have one singlet and one doublet.. anyone?

 

[admap]

That's exactly what I was getting at...

 

[atlanta213]

That's exactly what I was getting at...

Since we count adjacent carbon hydrogen, for the hydrogen on benzene, i count 1 and since we treat all 4 hydrogen on benzene as one, by n+1 it should be doublet.... I think..

 

[condoleezarice]

The chemical shifts on this benzene ring are so similar, it will appear to be a singlet. Try looking up the proton NMR shifts on chemoffice; it'll show a singlet.

 

[doc toothache]

http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALDRICH/W238600

 

[I-Baby]

You only use the n+1 rule when you are dealing with H's on adjacent C's that are NOT equivalent. That's the reason why the H's on the benzene ring are a singlet. It is because the are all equivalent. Same with the methyl H's.

 

[HowAboutDAT]

I'm pretty sure symmetry can explain this one. The molecule has vertical symmetry, causing there to be two "groups" of hydrogens, thus two singlets. Agree?