[rleung]

Hi,

I am confused as to why proton b has a chemical shift of 6.7, while proton c has a chemical shift of 7.5.  I would think that proton b would have a greater chemical shift since it is geminal to the C=O bond.  Thanks so much.

Ryan

[alphahydroxy]

I may be wrong with this - it is friday after all....

You probably want to think about the resonance forms of the a-b unsaturated ketone and consider whereabouts the electron density lies.

You should also bw aware of the fact that proton c is benzylic as well as bound to an sp2 carbon...

sorry for the fuzzy thinking...

[ArtemKulago]

My english is not good/ My minds is presented on the picture.

[laotree]

My english is not good/ My minds is presented on the picture.

The first structure explains the question very well.

[alphahydroxy]

ah, the universal language of organic chemistry :inlove:

[Winga]

I don't think the mesomeric effect is the main factor.

[Winga]

My explanation is that Hc and Hb are in different positions where Hc is closed to phenyl ring while Hb is closed to carbonyl group.

As the anisotropic effect by phenyl ring is higher than that by C=O group, Hc will have a higher chemical shift.