From lohl ^%at%^ obelix.uni-muenster.de Tue Jul 19 16:55:01 1994 Received: from obelix.uni-muenster.de for lohl: at :obelix.uni-muenster.de by www.ccl.net (8.6.9/930601.1506) id QAA09309; Tue, 19 Jul 1994 16:00:51 -0400 Received: from MARTINIQ.UNI-MUENSTER.DE by obelix.uni-muenster.de (AIX 3.2/UCB 5.64/4.03) id AA50093; Tue, 19 Jul 1994 22:01:48 +0200 Received: by martiniq.uni-muenster.de (AIX 3.2/UCB 5.64/4.03) id AA09871; Tue, 19 Jul 1994 22:01:35 +0200 From: lohl- at -uni-muenster.de Message-Id: <9407192001.AA09871 ^%at%^ martiniq.uni-muenster.de> Subject: SUM: radical cyclizations To: chemistry -A_T- ccl.net Date: Tue, 19 Jul 1994 22:01:34 +0200 (MES) X-Mailer: ELM [version 2.4 PL23] Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Content-Length: 6069 Hallo, A few weeks ago I posted a question concering radical cyclization and asked what there is anything known of its calculation. I have been asked to sum it for the others which is what I am doing with pleasure now. I would like to take the chance to say a big 'thank you' to all the contributers. It was a great help for me. The original question was: > For the explanation of experimental data I am interested > in finding the transition states of radical addition or > cyclisation reactions like for example a 6-exo-trig reaction. > Is there anyone aware of recent ab-initio or better semi-empirical > calculations which revealed the TS of any type of a radical addition > or cyclisation? These are the answers: ------------------------ You might want to look at this paper describing a force-field approach to modeling the transitions states of intramolecular cyclization reactions. (Spellmeyer and Houk, J. Org. Chem., 1987, 52(6), 959-974.) The force-field was optimized to produce minima that looked like the transition states of intermolecular radical additions calculated with ab initio methods. The force-field was further optimized to give accurate delta-Es for the regio-selectivity and stereo-selectivity observed in several intramolecular radical cyclization reactions. The accuracy of the model was tested by comparing TSs calculated using ab initio methods (UHF/STO-3G was the highest level we could run at the time) against the "transition states" we calculated using our force-field. They were nearly indistinguishable. These results differed from TSs calculated with MINDO/3, and MNDO. Beckwith and Schiesser have published a different force-field based on intermolecular TSs found using MNDO (Tetrahedron Letts, 1985, 26, 373). I hope this gives you a good place to start. I'd be happy to provide more information if you want. Good luck, David Spellmeyer Chiron Coporation 4560 Horton Street Emeryville, CA 94608 (510)-601-3313 Voice (510)-601-3360 FAX davids;at;cc.chiron.com e-mail ---------------------------------- Dear Dr.Loehl, I hope the following references on localization of TSs for addition reactions of radicals can be of some help. We are currently studying structure and reactivity of radical cations, but the kind of TSs on which we have long experience are those corresponding to internal migrations and abstraction processes. Anyway, if you have any specific question on metho- dological aspects, we will be pleased of trying to help you. [1] Features of the Potential Energy Surface for Reactions of OH with CH2O M.R.Soto and M.Page J.Phys.Chem., 1990, 94, 3242 [2] Computational Study of Addition and Abstraction Reactions between OH Radical and Dymethyl Sulfide. A Difficult Case. M.L.McKee J.Phys.Chem, 1993, 97, 10971 [3] Computational study of the Addition of OH radical to S=C=S M.L.McKee Chem.Phys.Lett., 1993, 201, 41 [4] Radical Addition to HNO. M.Page and M.R.Soto J.Chem.Phys., 1993, 99, 7709 [5] Addition of O(3P) to CF3O Z.Li and J.S.Francisco Chem.Phys.Lett., 1993, 209, 151 Yours, Laura <<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>> ! ! ! Laura Coitino ! ! Universita di Pisa - Dip.to di Chimica e Chim Industriale ! ! Via Risorgimento, 35. I-56100 Pisa, Italy ! ! Phone: Voice (+39-50)-918204 ! ! Fax (+39-50)-502270 ! ! E-mail: laurac%!at!%ibm580.icqem.pi.cnr.it ! ! : laurac $#at#$ ibm540.icqem.pi.cnr.it ! ! ! <<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>> ------------------------------------------ I've been doing computations of TS's for the addition of HO an (3P)O to va- rious compounds, mostly by semiempirical methods. Unfortunately I don't have a ref. list handy: what's been published has been in conjunction with exper- iments (silent discharge plasma decomposition). I find that Cl-containing compounds are quite difficult. For CHO compounds, the computations are rather straightforward: start from your product, do a reaction coordinate to sepa- rate it into reagents, pick the highest energy point to optimize to a transi- tion state..... (using keywords like TS in MOPAC--not NEARLY as successful as their writeup would have you believe--SIGMA in AMPAC--another tricky one-- LTRD, POWELL, NLLSQ-also in MOPAC). Do you have access to Chem Abstracts on- line? If so, it shouldn't be hard to do a literature search.... Let me know if you have some more specific questions. I have a lot of computer time avail- able, so could do a bit of trouble-shooting of your inputs. (Right now I have more computer time than my own time, but people have helped me in the past...) Irene Newhouse ----------------------------------------------- It's not a radical reaction, but I published ab initio work on a 6-endo-trig reaction in which focussed on the distortion of the TS due to the cycle. Here is the reference: C.I.Bayly and F.Grein, "Comparison of an intramolecular Michael-type addition to its intermolecular counterpart: an ab initio theoretical study", Canadian Journal of Chemistry, vol. 67, pp. 2137-2177 (1989). Christopher Bayly ------------------------------- Best wishes and thank you very much Thosrten -- |--------------------------------------------------------------------| |Thorsten Loehl Tel.:+49-251/83-3233 | |Inst. f. Organische Chemie Fax : -9772 | |Corrensstr. 40 Email:lohl:~at~:uni-muenster.de | |D-48149 Muenster | |Germany | |--------------------------------------------------------------------|