NMR shift question/TBR discrepancy?

[TheRelevant]

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Hey guys,

Hope the MCAT studying is going well! I was reviewing my conceptual understanding of NMR when I came across something that appeared discrepant in TBR O-chem (page 131). To paraphrase: apparently the presence of a carbonyl leads to magnetic shielding and therefore a downfield shift of the hydrogens on an adjacent carbon.

A couple points of contention:

1. Doesn't a carbonyl act as an electron-withdrawing group and DESHIELD the CH2 group (as opposed to shielding)?
2. Ignorning the first question (and let's assume its correct), they claim that shielding leads to a downfield shift (increased PPM). Isn't this incorrect? Shielding leads to an upfield shift (decreased PPM) as you would need to apply a stronger magnetic field to flip the hydrogen's spin.

Thanks for reading! Cheers.

 

[lumpyduster]

Yeah I agree with everything you've written. Increased electron density = upfield = smaller ppm; decreased electron density = downfield = larger ppm.

 

[pepocho]

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