Subject: Re: CCL:Light induced torsional movement

From: Daniel Kost <[email-masked]>
Date: Sun, 29 May 1994 09:22:43 +0300 (IDT)

On Thu, 19 May 1994 [email-masked] wrote:

> Hi everyone
> 
> I have a very interesting system in which an apparently torsional movement 
> (by 180 degrees), A-->B, is induced by UV light, and the reverse 
> transformation by heat. I want to eludidate the precise path and mechanism 
> 
> Your help is much appreciated.
> 
> 
> Charles Marais
> 
> 
> 

Without going into the computational detail, I would just like to comment
that a reaction which is "induced by UV light, and the reverse
> transformation by heat" - is quite impossible, since it would violate 
the principle of microscopic reversibility:  At least in the thermal part,
BOTH the forward and the reverse reactions should be "induced" to the 
same extent.
Daniel Kost
[email-masked]

---

From: [email-masked] (Akinori MURAKAMI)
Date: Sun, 29 May 94 17:32:20 +0900

We are also interesred in photocromic system.

>> > transformation by heat. I want to eludidate the precise path and mechanism 
It is difficult to calculate the excited potential surface.
In many case, the molecule is large and ab initio MCSCF, CI method can
not employed. And semiempirical method is not suitable for the excited
state potentail.

For thermal or ground state reation, we have been used a semiempirical
method MNDI-AM1 in MOPAC. Fortunently, the results are agreed with
experimental reaction energy with in 5 kcal/mol.

There is a case against the following comment. 

		TS
			Prodcuts

Reactant
A		C	B
	50		10

In the case, the reaction energy for reactant(A) much higher than that
of product(B). Thermal reaction will only occur for B -> A in room
temperature or so.