The tasks proposed in Spectroscopy challenge, I found two structures that are mostly similar in allylic moiety, the contradiction is presented below:

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Considering two carbons of the alkene bond, it could be easily seen that while the mesomeric effect contributes to the deshielding of beta-carbon on the right structure (143,0 ppm) which is much bigger than alpha-carbon (125,2), the opposite is predicted for the other structure, why is this?

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    $\begingroup$ Presumably the lower degree of substitution on the beta carbon compared to the alpha carbon in the open structure happens to cancel out the extra deshielding from the mesomeric withdrawal? Note that the methoxy CH3 in the open structure is also ~15 ppm more shielded than the CH2 in the closed structure. $\endgroup$ Mar 28 at 5:05
  • $\begingroup$ @NicolauSakerNeto-The source of your article is given as following: link.springer.com/book/10.1007/978-3-642-24390-5 $\endgroup$
    – user145005
    Apr 5 at 2:22


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