From: Sengen Sun (sengensun$##$yahoo.com)
Date: Thu Mar 23 2006 - 15:04:01 EST
--- "Boyles, David A." <David.Boyles$##$sdsmt.edu> wrote:
> Sengen:
>
> Would we be correct in summarizing your paper were
> we to state that "electron flow is induced by
> electron repulsion which is in turn induced upon
> molecular collision"?
>
This statement has a tiny problem. The closed-shell
electron flow is governed by ALL electrostatic forces.
But for neutral molecules such as those in the parent
D-A, a collision starts with e-e repulsion, which
predominantly contributes to the potential energy
increase in a collision. The N-N repulsion does exist
but is relatively less significant in the early stage
of a collision. It is common practice to say
electron-pushing mechanism in org chem, which does not
mean that N-N repulsion and e-N attraction don't
exist.
> Is this the "electron migration of CC's that has
> never been documented in the literature" as you have
> stated on slide 23(?) of your Powerpoint
presentation?
>
> Thanks,
>
> David
Anyway, you are right here, but not enough! None of
the closed-shell electron flows of any CCs had been
ever estalished at a theoretical level. That is, there
had never been concrete computational numbers to
support the electron-pushing mechanism for any CCs.
What we had on the electronic mechanism in the
literature is nothing but confusion. As I said, we
chemists lost our direction along the rings in
general, theoretically or by the intuition of
experimentalists. The three examples I already
discussed:
1. Hoffmann does not know the direction in his JACS
paper mentioned early on.
2. The parent D-A reaction had been a controversy ever
since. The electron-pushing mechanism had never been
accepted by high profile theoretical chemists. That is
why a concerted spin-recoupling was published (JACS
1998, 120, 3975), but as a mistake!
3. For the simple 1,3-dipolar cycloaddition shown on
Slide 16 (references therein) of my ppt file, all the
three possible mechanisms were proposed by three
different groups. Although Karadakov, et al. argued
for a correct one to me, but their data really do not
mean what they claimed!
Now, I have established concrete computational data to
support the electron-pushing mechanism as examplified
on slids 19 and 21.
Thanks for your contribution to the discussion.
Regards,
Sengen
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