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I recently stumbled upon a question that got me thinking. It goes something like this:

Find the major product of the following reaction:

Methylation of adenine

There were 3 options given:

Possible products

So it basically aims at finding out the most suitable $\ce{N}$ to attack the $\ce{CH3I}$.

i.e. The most nucleophilic $\ce{N}$ in adenine. At first, I felt that should be the $\mathrm{sp^3}$ hybridized amine group(7). But then I had to consider the delocalization of its lone pair in the ring. Then it struck me that I was forgetting about the base, which made me think about the possibility of the deprotonation of the $\ce{N}$(9) to make the 5-membered ring aromatic, which is in fact a very stabilizing phenomenon. Thus the electron density on it should be higher making it more nucleophilic. So I guessed the answer to be the first product given in this list.

I looked up in the internet for sources, but of no avail. I was just searching on this platform for further verification and I found a similar question regarding order of basicity of $\ce{N}$ in adenine. where @DavePhD pointed out that the $\ce{N}$(1) is the most basic one followed by 3 and 7. Thus suggesting probably option 3 in the list. Though I do know that basicity and nucleophilicity aren't simply the same, but still I cant just rule out the chance of me being wrong here.

So my question is whether or not my deductions are correct and if not, then I would be very obliged to get a detailed know-how about all the possible factors influencing the formation of major product in this reaction.

Acknowledgement: ChemDoodle 2D sketcher for helping me to draw the diagrams of organic compounds mentioned in this question.

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  • $\begingroup$ Each answer is missing a double bond. Would you please correct it? $\endgroup$
    – Mathew Mahindaratne
    Commented Jan 18, 2020 at 15:29
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    $\begingroup$ I go ahead and corrected the structure. And also, $\ce{N}$7 is not $\mathrm{sp^3}$-hybridized here. $\endgroup$
    – Mathew Mahindaratne
    Commented Jan 18, 2020 at 16:32
  • $\begingroup$ Oh I'm very much sorry. Actually the double bond wasn't there in the options though , it was definitely a typo. Thanks for the edit. And yeah why don't you call the $\ce{-NH2 sp3}$ ? Is it because its delocalized? Also could you provide any insight into the reaction as such? $\endgroup$
    – Sir Arthur7
    Commented Jan 18, 2020 at 18:56

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