Topic: another chemical shift question (Read 6021 times)

rleung · « **on:** August 05, 2005, 11:12:05 AM »

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 · « **Reply #1 on:** August 05, 2005, 12:16:07 PM »

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 · « **Reply #2 on:** August 08, 2005, 08:56:03 AM »

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

laotree · « **Reply #3 on:** August 08, 2005, 10:50:14 PM »

Quote from: ArtemKulago on August 08, 2005, 08:56:03 AM

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

The first structure explains the question very well.

alphahydroxy · « **Reply #4 on:** August 09, 2005, 09:37:06 AM »

ah, the universal language of organic chemistry :inlove:

Winga · « **Reply #5 on:** August 09, 2005, 10:17:14 AM »

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

Winga · « **Reply #6 on:** August 09, 2005, 10:24:17 AM »

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.

Topic: another chemical shift question (Read 6021 times)

rleung

another chemical shift question

alphahydroxy

Re:another chemical shift question

ArtemKulago

Re:another chemical shift question

laotree

Re:another chemical shift question

alphahydroxy

Re:another chemical shift question

Winga

Re:another chemical shift question

Winga

Re:another chemical shift question

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