TBR, Organic Chemistry, Section 2, Passage 9, Question 58

[sillyjoe]

The question asks:

58. Spectrum 1 is associated with the:

A. trans compound, because the J value is smaller
B. cis compound, because the J value is smaller
C. trans compound, because the J value is larger
D. cis compound, because the J value is larger

Choice C is correct. In Spectrum I, the distance between the peaks in the alkene region (coupling constant) is greater than it is in Spectrum II. A larger coupling between vinylic hydrogens is attributed to the trans compound. This is choice C.

I am just not seeing it. Can someone please help explain this to me? I don't see a difference in any distances in the figure.

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[sillyjoe]

.

 

[ryguy87]

I also have the same problem, Is this just an error on the peaks...? Can anyone help?

 

[EParker37]

The shift values are identical. This is probably a misprint.

 

[Cawolf]

It's not the shift values, but the J values that would indicate the dihedral angle of the protons.

I can't tell from the picture, so who knows. The explanation is right but I don't think that you could deduce a difference in frequency by looking.

 

[EParker37]

It's not the shift values, but the J values that would indicate the dihedral angle of the protons.

I can't tell from the picture, so who knows. The explanation is right but I don't think that you could deduce a difference in frequency by looking.

Yeah, that's right, I haven't looked at NMR in a while. For some reason I remember being able to calculate freq from shift, but I probably am mis-remembering lol.

 

[Cawolf]

I am in Organic 2 right now and actually just had to do this for a lab comparing cycloaddition mechanisms.

 

[EParker37]

I am in Organic 2 right now and actually just had to do this for a lab comparing cycloaddition mechanisms.

Nitration? I remember doing nitration of methyl benzoate and using NMR to analyze the products.

 

[Cawolf]

It's actually a [3+2] addition of stilbene (cis or trans) and benzonitrile oxide.

 

[ryguy87]

Thx guys