[notsheldoncooper]

Hi, I have some questions about proton and carbon NMR of acetaminophen. On carbon NMR spectrum, the quaternary carbon (from benzene ring) linked to -OH is more deshielded than the one linked to the amide group. How come? On proton NMR the two peaks for hydrogen from benzene are as  I expected - the one closer to -NH is more deshielded and I saw the same on C-NMR with regard to those carbons. Why then the quaternary carbons seem to be opposite to that?

Second question, about MS - I have been trying to figure out the fragmentation pattern of that molecule. I understand how the m/z 109 is formed. What about the one at m/z 80? There is a loss of formaldehyde by McLafferty rearrangement but how does the mechanism occur? Does it start from -OH group that loses hydrogen? I can't understand the steps of that rearrangement.

I would be grateful for any suggestions
Thanks

[Babcock_Hall]

The quaternary carbon attached to oxygen is more deshielded because of induction from the more electronegative atom.  What is your explanation for the carbon NMR chemical shifts of the carbons bonded to hydrogen?

[Irlanur]

the quaternary carbon (from benzene ring) linked to -OH is more deshielded than the one linked to the amide group. How come?

"shielding" is not the primary cause of 13C chemical shifts. It has mainly to do with "paramagnetic" shifts from low lying orbitals. Anyway, it often looks that "shielding" is an appropriate explanation.