J Coupling question

[Vokalyzd]

I'm at the end of my DAT studying (April 5th!) and I still have problems with J coupling. I was able to do it in school but Kaplan doesn't offer a really coherent explanation and wikipedia was no help. I have the DAT Destroyer but as you know, those are just questions! If somebody can provide a link or a suggestion of J Coupling explanation, that would be great! I know the question is low yield but hey..every point matters

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[AmpedUp]

Refresh my memory about J Coupling. Is that in Organic Chem?

 

[Vokalyzd]

Yeah it's Ochem..it's H-NMR splitting. I get the concept and I understand the Pascal table. My only concern is if the question asks for triplet/doublet or singlet/doublet, I can't immediately see the molecular composition nor figure it out.

 

[AmpedUp]

Yeah it's Ochem..it's H-NMR splitting. I get the concept and I understand the Pascal table. My only concern is if the question asks for triplet/doublet or singlet/doublet, I can't immediately see the molecular composition nor figure it out.

Ahh yeah! I can't say I can help you there. I struggled with NMR, so I refrained from going overboard on the topic. I just memorized some numbers and looked at the number of signals and chose an answer on the real thing.

 

[Vokalyzd]

Which numbers did you memorize? I memorized all of the IR spec numbers but there is no J-coupling splits to memorize besides Pascal triangle

 

[Maygyver]

The rule of thumb is that you take the number of neighboring hydrogens and add one to get the splitting pattern.
For example, if you have an ethyl group: -CH2CH3 you will get a triplet and a quartet. The triplet is from the methyl groups hydrogens being split by the 2 neighboring hydrogens, and the quartet is from the CH2 hydrogens being split by the 3 methyl hydrogens.
I'm not sure if this is what you are asking exactly. Hopefully it helps.

 

[Vokalyzd]

That simplifies it so much. Thank you! So if the question mentions a singlet, it means that there are no adjacent hydrogens to the hydrogen in question?

 

[Maygyver]

That simplifies it so much. Thank you! So if the question mentions a singlet, it means that there are no adjacent hydrogens to the hydrogen in question?

Yep! I think for the most part, just knowing the n+1 rule should work for the dat. I remember in ochem lab having to worry about things like doublets of quartets and such, but for most of the practice problems I have seen for the DAT its usually kept to problems you can use n+1 to solve.

 

[Vokalyzd]

Thanks for all the replies! That's one less thing to worry about..now Ecology scared: