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Which N atoms in caffeine is the least basic

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joc:
Please help.

Pls refer to the attached file for the structure of caffeine.

The question is which N atom in caffeine is the least basic.

I think the Ngamma is the least basic because the electron pair is involved in an aromatic ring system (Huckel's rule).  However, some suggest that it is the Nbeta is the least basic because the lone pair is delocalized to the two neighbouring strongly electron withdrawing C=O groups.  Which one is more likely to be true?

Thanks a million!

joc

Doc Oc:
I would also wager on beta, but I'm not an expert with nucleotide chemistry.

Schrödinger:
Something tells me it is Nbeta.

When you try to draw some of its resonance structures, you can come up with the following(see figure attached) :

In addition to the stabilization due to aromaticity in the figure, the beta N is attached to 2 C=O groups.

I'm definitely not sure, but I thought I'd give it a shot


Oh...and one more thing. How do I attach a figure without having to attach a file?
I mean can I copy a picture from Chemdraw and just paste it here?

nj_bartel:
My guess would be beta too.

joc:
Thanks for your input. 

By the way, is there any source on the internet on the data of pKb values or pKa values of the common natural organic compounds such as caffeine.  What I mean is for all the N atoms or OH groups.  I have tried to search but can only get the values for the most basic one or the most acidic one.

Thanks again.

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