NMR Spectrum - expected triplets appear as singlets

[chemistryfourm]

TL;DR Summary

My NMR of diethyl cyclopent-3-ene, 1, 1 , dicarboxylate shows the cyclic proton environments both as singlets where they are expected to be a doublet and triplet

My NMR of diethyl cyclopent-3-ene, 1, 1 , dicarboxylate shows the cyclic proton environments both as singlets where they are expected to be a doublet and triplet.
Proton env B would be epxected to be a doublet and D to be a doublet. Everyone in the lab got the same result. Is there an explanation as to why it they are singlets and not multiplets as expected? The chemical shift and integration suggest they are the expected proton enviornment however the multiplicity is not as expected.

 

[Tom.G]

It seems there are only 4 general possibilities:
1) the specimens are not what you think they are
2) plot resolution is not sufficient to resolve close peaks
3) NMR machine needs servicing
4) you have an incorrect expectation of results

Cheers,
Tom

p.s. Please let us know what you find causing the effect.
(we all like to learn!)

 

[Borek]

It seems there are only 4 general possibilities:

There is more, for example in some molecules resonance can change the "average" observed structure, making the spectra different from the one that looks obvious and logical. I doubt that's the case here though.

 

[DrJohn]

I think it is the orientation of the hydrogens in the ring. Check the Karplus equation. You will see that certain orientations lead to low values for J(H-C-C-H). The protons at the double bond - D - are in the plane of the ring, the ones at position B are on tetrahedral carbons and not in the same plane.

So then I googled the proton spectrum of your product, and got the same spectrum as you have.
See this https://www.rsc.org/suppdata/cc/b6/b618341g/b618341g.pdf and look at the first spectrum.

I actually googled proton nmr of cyclopent-3-ene first and up came your product.

 

[chemisttree]

What effect does the symmetry of the molecule have on the observed spectrum?