[rengb6]

Hello, I am studying for my orgo final using old exams the teacher has posted. But splitting trees really have me confused. Here is the question.

Before I even get started I can guess that because the compound is vinylic the chemical shift is between 4.5 and 6.5. Is this accurate? The J values are as followed: J12= 7, J13= 2. J14= 2, J34=1.5, J23=12, J24=15.

From these is it correct to say that each H will be split 3 times because they are seen in three J values each? For example if I chose H2 I would need to include in my splitting tree J12, J23, and J24. To di this splitting tree I would start at J24 because its the highest number. Here is what I came up with


A few questions. I started with 15 because that was the J value for J24. Would I continue to split this number as I go down the tree or would I use the next J value? For example, the second line of the tree was for J23 whose value was 12, do I split 12 into 4 pieces or 15 into 4 pieces? Also, how do i know when lines will intersect? Like for my last line how do I know there are 8 final solid lines and not 6? Would they intersect if the J values for 3 and 1 were the same?

Finally, how do I determine the chemical shift? Thanks for any tips and *delete me*

[Dan]

You have implied splitting from coupling to to H₁, which does not exist. There are only 3 protons. The substituents are CN, H₂, H₃ and H₄.

[rengb6]

I can see what you mean thank you! So would this just be a doublet and I would get rid of the last row of splitting? How would I go about determining the chemical shift?

[rengb6]

I think that since H3 is farthest away from Nitrogen its chemical shift will be closer to 6.5. H2 is closest to the nitrogen so its chemical shift will be closer to 4.5 and H4 is on the same side of the nitrogen (closer than H3) but farther away than H2 so its chemical shift will be 5.5. Could this be correct? I belueve the question wants estimations.

[Dan]

So would this just be a doublet and I would get rid of the last row of splitting?

Yes, you need to remove the last row of splitting from the tree diagram you originally drew. The result of doing that is not a doublet though is it?

[rengb6]

Its a quartet! would the ration be 1:3:3:1?

[Babcock_Hall]

When a nucleus experiences nonidentical (in terms of J values) coupling to two other nuclei, the result is called a doublet of doublets.

[Dan]

Its a quartet! would the ration be 1:3:3:1?

No, as mentioned above it is a double doublet, the ratio is 1:1:1:1