I understand that this molecule can only act as a Brønsted base because it is sterically hindered by its multiple methyl groups.

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However, isn't the proton bound up in solution? Doesn't that increase the effective size of the proton? How then exactly is a proton expected to reach the site of basicity if it's tied up with multiple water molecules? Or is the size of the hydrated proton still quite small? Or does the proton separate from the water molecules once the proton is sufficiently close to the site of basicity (the lone pair on the nitrogen)?

  • $\begingroup$ I don't think there will be steric hinderence to a small cation proton $\endgroup$ – RE60K Aug 15 '14 at 3:28
  • $\begingroup$ Right but we know for a fact the proton is solvated quite heavily in water, with many users on this very forum insisting that H3O+ is inadequate to describe the extent of solvation of the proton in water. So wouldn't this solvation bulk up the proton? $\endgroup$ – Dissenter Aug 15 '14 at 3:31
  • $\begingroup$ did you reseacrched its pKa, it is 11.07, stronger than methylamine, carbonate,phenoxide,ammonia,etc. $\endgroup$ – RE60K Aug 15 '14 at 3:35
  • $\begingroup$ pKa of what? Hydronium ion? Also I don't see phenoxide ion as having a particularly high pKa in the first place. $\endgroup$ – Dissenter Aug 15 '14 at 3:37
  • $\begingroup$ see here, you do no research on google?, it is stronger than unhindered amines. $\endgroup$ – RE60K Aug 15 '14 at 3:39

I don't see much hinderance[note that they all have been optimised to stable configurations] Blue: nitrogen,White: Hydrogen,Grey: Carbon

Side View:

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Top View:

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| improve this answer | |
  • $\begingroup$ The methyls on the left seem eclipsed in the top pic, is that the most stable conformed? Also can another Lewis acid get to the lone pair on nitrogen? I.e would say a metal cation be too big to fit? $\endgroup$ – Dissenter Aug 15 '14 at 4:34
  • $\begingroup$ @Dissenter I just used optimise geometry function and this is what i got. $\endgroup$ – RE60K Aug 15 '14 at 4:36
  • $\begingroup$ Cool. What program? $\endgroup$ – Dissenter Aug 15 '14 at 4:37
  • $\begingroup$ @Dissenter avogardo $\endgroup$ – RE60K Aug 15 '14 at 4:44

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