Hi cheu,

You has very large and multiple aromatic ring you do not now exact geometry for the molecule therefore you can explain your observation by saying that OH is laying in shielding zone of the rings and C=N. good Luck

Hello Jubyeong,

The hydroxyls are most likely shifted downfield because of hydrogen bridging to the nitrogens. This would also explain the broad signals for the asymmetric molecules. The hydroxyls are in slow exchange with each other.

I am not completely convinced that you have the rest of assignments right. For example in the second molecule from the top you label a singlet as 2. But the atom on the molecule with the label should be a doublet with ca 7Hz coupling. I think the singal you point to belongs to the proton on the other side. Do you have a picture with better resolution. It would easier if the individual multiplets could be better identified.

Clemens

This may be due to the ring current effect

Dear all, Salim, Clemens, Murad, thank you guys answers.

Then, how could I explain about the most deshielded -OH peaks?

Its movement is contrary to other protons.

Low field shift of OH protons is mainly due to hydrogen bonding OH-N as one of colleagues said. So your substitutes influence mainly on H-bonding. May be you will sucseed in explaining from that point of veu.

Dear Jubyeong Chae,

I agree with Clemens about the question of the assignments for the second from the top molecule. Indeed, a better resolved spectrum would be helpful. Please note also that DMSO is a strong hydrogen-bond acceptor, and tends to move OH (and NH) signals downfield (to higher frequency). It might be interesting to see a comparison of the OH chemical shifts of your compound(s) in both DMSO-d6 and CDCl3 (if soluble).

Good luck in your research!