[nokia8650]

Why are 40 and 41 in different environments?  I presume it is something to do with the 3d arrangement, however please could someone explain this?

Thanks alot in advance

[Borek]

I wonder... Is the head of nanoputian flat?

[Dynamic]

Look at the bond between C21 and C36. 

[James Newby]

Have you thought about chair conformations of 6 membered rings?

[Dynamic]

Is this 1,3-dioxane ring likely to have a significant barrier to inversion?  I don't think so.

It is due to the fact that there is another chiral center on the ring.  This places one of the protons closer to the 'interior' of the molecule (closer to the ring current of both aromatic rings) and it places the other proton further away. 

Totally different chemical environments.

[James Newby]

I was thinking the aromatic group would be too bulky to be in the axial position due to 1,3 steric clash.  This would lock the ring in one conformer giving the two different hydrogen environments axial and equatorial.  The NMR signals would be similar but the coupling constants should be different

[alphahydroxy]

I was thinking the aromatic group would be too bulky to be in the axial position due to 1,3 steric clash.  This would lock the ring in one conformer giving the two different hydrogen environments axial and equatorial.  The NMR signals would be similar but the coupling constants should be different

I think this is correct, and C36 is not chiral.

With such a large "R" group at C36, the conformation of the ring will be locked, and those two methyl groups will be in different environments.