From kostd@bgumail.bgu.ac.il Sun May 29 02:42:06 1994 Received: from bgumail.bgu.ac.il for kostd@bgumail.bgu.ac.il by www.ccl.net (8.6.4/930601.1506) id CAA26350; Sun, 29 May 1994 02:30:49 -0400 Received: by bgumail.bgu.ac.il (5.65/DEC-Ultrix/4.3) id AA00466; Sun, 29 May 1994 09:27:48 +0300 Date: Sun, 29 May 1994 09:22:43 +0300 (IDT) From: Daniel Kost Subject: Re: CCL:Light induced torsional movement To: chuck@mickey.iaccess.za Cc: chemistry@ccl.net, Chuck@psipsy.uct.ac.za In-Reply-To: <01HCIZ380EWI9867D3@Uctvax.UCT.AC.ZA> Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII On Thu, 19 May 1994 chuck@iaccess.cstat.co.za 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 kostd@bgumail.bgu.ac.il From mei@atlas.rc.m-kasei.co.jp Sun May 29 04:42:07 1994 Received: from frontier.m-kasei.co.jp for mei@atlas.rc.m-kasei.co.jp by www.ccl.net (8.6.4/930601.1506) id EAA26942; Sun, 29 May 1994 04:37:49 -0400 Received: from atlas.rc.m-kasei.co.jp (atlas.rc.m-kasei.co.jp [133.251.253.2]) by frontier.m-kasei.co.jp (8.6.8+2.4Wb/3.3Wb-m-kasei) with SMTP id RAA24183; Sun, 29 May 1994 17:32:44 +0900 Received: by atlas.rc.m-kasei.co.jp (4.1/6.4J.6) id AA01662; Sun, 29 May 94 17:32:20 JST From: mei@atlas.rc.m-kasei.co.jp (Akinori MURAKAMI) Message-Id: <9405290832.AA01662@atlas.rc.m-kasei.co.jp> To: Daniel Kost Cc: chuck@mickey.iaccess.za, chemistry@ccl.net, Chuck@psipsy.uct.ac.za, mei@atlas.rc.m-kasei.co.jp Subject: Re: CCL:Light induced torsional movement In-Reply-To: Your message of Sun, 29 May 94 09:22:43 +0300. Date: Sun, 29 May 94 17:32:20 +0900 We are also interesred in photocromic system. >> > 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 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. >> 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 >> kostd@bgumail.bgu.ac.il From chuck@iaccess.cstat.co.za Sun May 29 08:42:13 1994 Received: from mickey.iaccess.za for chuck@iaccess.cstat.co.za by www.ccl.net (8.6.4/930601.1506) id IAA28398; Sun, 29 May 1994 08:00:34 -0400 Received: from slipper225.cstat.co.za by mickey.iaccess.za with smtp (Smail3.1.28.1 #1) id m0q7jX3-0004MYC; Sun, 29 May 94 13:59 GMT+0200 Message-Id: From: "Charles Marais" To: chemistry@ccl.net Date: Sun, 29 May 1994 13:51:09 MIME-Version: 1.0 Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT Subject: Re: CCL:Light induced torsional movement Reply-to: chuck@iaccess.cstat.co.za Priority: normal X-mailer: Pegasus Mail/Windows (v1.11a) Daniel Kost wrote: >> 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 >> kostd@bgumail.bgu.ac.il I should perhaps have clearer - We don't know that the forward and reverse paths are the same, just that the molecule proceeds from A->B when you shine light on it, and from B->A when you heat it. The mechanisms may be quite different. Charles gumail.bgu.ac.il ---------------------------------------------------------------------------------------- Charles Marais Phone 27-21-788-2248 Southern Scientific Fax 27-21-788-6613 17 Capri Rd Email Chuck@iaccess.cstat.co.za St James Chuck@psipsy.uct.ac.za South Africa 7700 -----------------------------------------------------------------------------------------