Stability of pyridine derivatives Arrange the following pyridine derivatives in the order of increasing stability
of adduct formed with $\ce{BBr3}.$ Explain briefly.


I'm pretty confused about which structure is the most stable. I'd say structure III is the most stable as it has two methyl groups to donate electrons to nitrogen and increase its Lewis basicity.
However, I think III may not be the most stable because of steric hindrance. In fact, structure II could be the most stable as the methyl group is closer to nitrogen and there's no steric hindrance. Therefore, the answer should be III &lt; I &lt; II.
Is my reasoning correct? Are there any factors to consider for stability?
I believe that the order of stability is II &gt; III &gt; I. The adduct should be formed between the lone pair on nitrogen and the Lewis acid. From there, I would apply the M+, I+ effects of the methyl groups as are known from benzene derivatives (although the substitution chemistry of pyridine is different from benzene).