[Dan]

For mechanism 1 and 3, we should be able to compare the strength of the bases from the acidities of the conjugate acids. If we compare the acidity of CH5(+) with CH3OH2(+), I believe CH3OH2(+) is more acidic. I argue that bromine is more likely to react with the lone pair of the oxygen than the bonded pair of the CH bond.

I assume you meant CH₅⁺ is more acidic, I agree with you. I do not doubt that hypobromites will form...

That doesn't prove the mechanism occurs in that manner.

I would argue that in order for the CH bond to lead to oxidation, the formation of a hypobromite should be reversible and unproductive.

Agreed

In a way, this could be similar to a pinacol rearrangement. Do they show any stereoelectronic effects with a similar electron release?

Agree with the pinacol analogy, I was also thinking along the lines of Hofmann/Beckmann rearrangement chemistry. The problem with the pinacol rearrangement is that (as I understand it) the RDS is loss of water to form a carbocation, whereas I think we will agree that an analogous intermediate would not form the Br-X oxidation (scheme).

I'm not sure about the validity of comparing Hofmann/Beckmann rearrangement kinetics either... what do you think?

[orgopete]

Dan,

Thanks for picking up my obvious error on the acidity note.

Re: stereoelectronic effects
Clearly we can find them in many reactions. The Hoffmann rearrangement is sensitive to the orientation of the oxime and can give different products from each. I believe the pinacol does also, but I am not familiar with any bona fide results to quote.

If anyone is paying attention, you can discern that I like to group things together. While I wouldn't normally link the stereoelectronic demands of a Hoffmann rearrangement with a hypobromite oxidation, I would if that was the best I could do. I think very carefully about how a pair of electrons react. How are the non-bonded electrons of hydronium ion different from hydroxide or water? They have the same charge (-2). I find it comes to distance which is compatible with the inverse square law.

Clearly, I was being methodical in suggesting a pinacol rearrangement as it placed a leaving group on a carbon beta to migrating group. You simply expanded this to consider other mechanistically similar reactions. I think when this is done in a general case such as this, then we should find most reactions have some kind of precedence or expectations as to what might occur. The suitability, it seems to me, would be the similarity of the driving forces in a reaction. If you have a migration due to a pushing from a lone pair of electrons, a quite different result may (not will) occur in the absence of the lone pair.