December 04, 2023, 02:44:09 PM
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Topic: Relative chemical shift of diastereotopic vinylic hydrogens  (Read 3440 times)

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Offline OrganicH2O

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I was looking at this Sapling homework and the student is supposed to determine the relative chemical shift of 'A' vs 'B' (shown in an attached picture), which are diastereotopic vinylic methylene hydrogens.

It seems to me the only obvious way to tell them apart would be the relative coupling constant. 'A' should have a larger coupling constant with 'C' because it is trans to 'C'. This was pretty hard to even read in the question, because there was no zoom on the relevant splitting patterns.

According to whoever wrote the question on this Sapling assignment,  'A' should have a higher chemical shift because it is "closer to the oxygen". Does this logic make any sense? A and B the same bond distance away from the oxygen. Is there any obvious relationship in terms of closeness in physical space that correlates with chemical shift?
I have a Master's in organic chemistry and I am exposed to a LOT of different introductory organic chem classes in the course of my work, ranging from very basic to Harvard. I am here to refine my knowledge and consult with other organic chemistry nerds.

Offline Babcock_Hall

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Re: Relative chemical shift of diastereotopic vinylic hydrogens
« Reply #1 on: June 15, 2021, 03:26:08 PM »
Personally I would use the coupling constants.

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