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In the molecule pictured on the photo, nitrogen atom number 7 looks the most basic. It is 2 degree, the lone pair is localized and there is no resonance, so it should accept the proton readily.

But the given answer is 3. Why is that?

To find the nitrogen atom which will most readily accept proton we see the lone pairs of nitrogen atom so here Nitrogen number 1,2,4,6 and 8 have their lone pairs delocalised by resonance so they will not readily accept the proton so the most probable answers will be 3,5,7 or 9 .

Question

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    $\begingroup$ Note that guanidine has pKb 0.4, what makes it much stronge base than dimethylamine ( pKb 3.29) $\endgroup$
    – Poutnik
    Jun 21 at 8:08
  • $\begingroup$ I agree, the guanidine will be by far the most basic centre. 3 is a benzylamine pKb around 4.6 $\endgroup$
    – Waylander
    Jun 21 at 8:10
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    $\begingroup$ @Maurice A title can be a question. But it should not be like the whole question. For the OP: Compare suitable titles with analogies of book titles or article headlines. $\endgroup$
    – Poutnik
    Jun 21 at 8:10
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    $\begingroup$ Imagine you are an editor of the Science magazine. Your have received an artitle titled Nitrogen number 7 is 2 degree and the lone pair is localised so it should accept the proton readily but the answer is given 3 ? Why is that? Would you accept such an article? $\endgroup$
    – Poutnik
    Jun 21 at 8:46
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    $\begingroup$ And what would accept proton readily mean, really? This could be a kinetic problem, but that means it's pretty pointless, as all such reactions are very fast. $\endgroup$
    – Mithoron
    Jun 21 at 12:35

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