From chemistry-request@server.ccl.net Thu Apr 27 03:58:50 2000 Received: from maile.surrey.ac.uk (maile.surrey.ac.uk [131.227.102.10]) by server.ccl.net (8.8.7/8.8.7) with SMTP id DAA16804 for ; Thu, 27 Apr 2000 03:58:49 -0400 Received: from lt-ces1mb (actually host ip192.cpe.surrey.ac.uk) by maile.surrey.ac.uk with SMTP Local (PP); Thu, 27 Apr 2000 08:57:42 +0100 Message-Id: <3.0.5.32.20000427085944.0086fc30@pop.surrey.ac.uk> X-Sender: ces1mb@pop.surrey.ac.uk X-Mailer: QUALCOMM Windows Eudora Light Version 3.0.5 (32) Date: Thu, 27 Apr 2000 08:59:44 +0100 To: chemistry@ccl.net From: Dr Mark J Biggs Subject: QM study of heterogeneous reactions - 2 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Hi All! have had two very helpful replies to my original question so far - many thanks to these people. Further comments are welcome. I must make a correction to my original e-mail and would like to offer more thoughts: The O-down config in the paper I quoted was less stable than N-down - this is why they used O-down. However, this fact does not change the thrust of my original question - I am trying to get to the bottem of why any given start point is used in preference to another OR, more importantly, why we should not consider possibilities as a function of: angle of approach as well as orientation of molecule and temperature. One of the responses I have got so far makes it clear that temperature can be very important and that the O K path may be much in error. Here are some more of my thoughts on this - I welcome all comments: The standard approach taken in many papers appears to assume that one can start from a single particular configuration and that only the transition states of the various elementary steps leading away from that point are important. In a real system, molecules will approach from a range of angles and with a range of orientations and with a given kinetic energy, all of which will dictate the reaction path taken, if reaction infact occurs at all. Is it correct to say that QM as done in the paper I cite (and others) cannot account for this situation and, therefore, conclusions will never be definitive but, rather, always dependent upon the initial assumed state? If we had all the computer power we wanted, would QM in the case be done differently? (e.g. do QM MD with lots of molecules and active sites and let the system "react" and accumulate staistics - i.e. much as we do in classical MD for transport properties). Many thanks in advance. Regards, Mark From chemistry-request@server.ccl.net Thu Apr 27 03:58:59 2000 Received: from phare.univ-lille2.fr (root@phare.univ-lille2.fr [193.51.138.40]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id DAA16802 for ; Thu, 27 Apr 2000 03:58:48 -0400 Received: from icpl6 ([192.168.120.111]) by phare.univ-lille2.fr (8.8.7/8.8.7) with SMTP id IAA32207 for ; Thu, 27 Apr 2000 08:56:10 +0200 Message-ID: <002001bfb01e$35d210d0$6f78a8c0@icpl6.univ-lille2.fr> From: "Philippe CHAVATTE" To: "CCL" Subject: Journees Franco-Belges de Pharmacochimie - Lille Date: Thu, 27 Apr 2000 09:57:18 +0200 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 4.72.3110.5 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 XIVemes JOURNEES FRANCO-BELGES DE PHARMACOCHIMIE De la Conception à la Realisation en Pharmacochimie 25 et 26 Mai 2000 - Lille (France) Comite permanent d'organisation: A. Delarge (Liege) P. Depreux (Lille) P. Formstecher (Lille) J.P. Henichart (Lille) R. Houssin (Lille) D. Lambert (Louvain en Woluwe) D. Lesieur (Lille) V. Loppinet (Nancy) B. Masereel (Namur) J. Neve (Bruxelles) B. Pirotte (Liege) J. Poupaert (Louvain en Woluwe) S. Rault (Caen) P. Seck (Luxembourg) E. Tschirhart (Luxembourg) Programme: Jeudi 25 Mai 2000 9 h 00 Ouverture Section A. UTILISATION D’UN MODELE D’ORIGINE NATURELLE 9 h 30 Olivier LAVERGNE (Institut Beaufour – Les Ulis) Derives de la Camptothecine à lactone stabilisee 10 h 30 Communication orale 10 h 45 Pause et Communications par affiches 11 h 15 Arnold VLIETINCK (Universite d’Anvers) Plants as useful source of pharmacologically interesting lead compounds 12 h 15 Communications par affiches 12 h 45 Repas Section B. 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(33) 03 20 96 40 40 Poste 4256 ou 4219 - Fax (33) 03 20 96 43 61 E-Mail : jolegrand@phare.univ-lille2.fr ====================================================================== Philippe CHAVATTE Institut de Chimie Pharmaceutique Albert Lespagnol BP 83 59006 LILLE CEDEX FRANCE E-Mail : pchavatt@phare.univ-lille2.fr From chemistry-request@server.ccl.net Thu Apr 27 08:05:41 2000 Received: from smtprelay.ruc.dk (smtprelay.ruc.dk [130.225.220.22]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id IAA18729 for ; Thu, 27 Apr 2000 08:05:38 -0400 Received: from virgil.ruc.dk (virgil.ruc.dk [130.225.220.110]) by smtprelay.ruc.dk (8.9.3/8.9.3) with ESMTP id OAA14332; Thu, 27 Apr 2000 14:01:02 +0200 (MET DST) Received: from VIRGIL/SpoolDir by virgil.ruc.dk (Mercury 1.44); 27 Apr 00 14:13:39 +0100 Received: from SpoolDir by VIRGIL (Mercury 1.44); 27 Apr 00 14:13:35 +0100 From: "Jens Spanget-Larsen" Organization: Roskilde Universitetscenter To: "Yeoh Hak Koon" Date: Thu, 27 Apr 2000 14:13:17 +0100 Subject: CCL:HOMO-LUMO vs. lambda max CC: chemistry@ccl.net Priority: normal X-mailer: Pegasus Mail for Windows (v2.23) Message-ID: <14FD743013D@virgil.ruc.dk> Yeoh Hak Koon: > What are the reservations or objections of equating the HOMO-LUMO energy gap > to the maximum wavelength peak (lambda max) in a UV-Vis spectra? Equating a molecular orbital energy difference to an electronic excitation energy is wrong, primarily for two reasons: 1) The energy required to promote an electron from orbital i to orbital j is not at all equal to the energy difference e(j) - e(i). The promotion energy E(i-->j) can be expressed as E(i-->j) = e(j) - e(i) - v(i,j) where the term -v(i,j) represents the interaction between a hole in orbital i and an electron in orbital j. This term may be relatively small if the two molecular orbitals are spatially separated, but in general, v(i,j) amounts to several electron volts and is by no means negligible. 2) The wavefunction |i-->j> of an excited electronic configuration is not in general a good approximation to an eigenfunction of the many-electronic Hamilton operator H. Generally, matrix elements corresponding to j|H|k-->l> are not close to zero. Hence, excited configurations tend to interact, and a proper description must include Configuration Interaction, (CI). Of particular importance is the first order CI between near-degenerate configurations of the same symmetry, f.inst. for alternant hydrocarbons where it gives rise to "plus" and "minus" states. - Inclusion of multiply excited configurations (like i,k-->j,l etc.) in the CI formally accounts for electronic correlation effects, thus leading to a description going beyond the orbital picture. However, semiempirical CI-procedures (PPP, CNDO/S, INDO/S, ZINDO, etc.) usually limit the CI expansion to singly excited configurations, and account for correlation effects by empirical adjustment of parameters in the models. Yours, Jens >--< =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= JENS SPANGET-LARSEN Phone: +45 4674 2000 (RUC) Department of Chemistry +45 4674 2710 (direct) Roskilde University (RUC) Fax: +45 4674 3011 P.O.Box 260 E-Mail: JSL@virgil.ruc.dk DK-4000 Roskilde, Denmark http://www.rub.ruc.dk/dis/chem/psos/ =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= From chemistry-request@server.ccl.net Thu Apr 27 10:03:02 2000 Received: from jivdhan.unipune.ernet.in (jivdhan.unipune.ernet.in [196.1.114.31]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id KAA19400 for ; Thu, 27 Apr 2000 10:03:00 -0400 Received: from chem.unipune.ernet.in (chem.unipune.ernet.in [196.1.114.10]) by jivdhan.unipune.ernet.in (8.9.0/UnipuneMailhubV1.3) with ESMTP id TAA08520 for ; Thu, 27 Apr 2000 19:22:08 +0530 Received: (from tcg@localhost) by chem.unipune.ernet.in (8.8.7/8.8.7) id TAA25381 for chemistry@ccl.net; Thu, 27 Apr 2000 19:56:30 +0530 Date: Thu, 27 Apr 2000 19:56:30 +0530 From: "Students of Dr. S.R. Gadre" Message-Id: <200004271426.TAA25381@chem.unipune.ernet.in> To: chemistry@ccl.net Subject: Molecular Recognition April 27, 2000 It is more than 100 years. since E. Fischer proposed his famous term "lock and key." Does anybody remember a simple, lucid discussion of this principle? Ofcourse, such discussion should be electronic nature, barring the interactions such as 'inert gas...inert gas' and should be beyond steric factor consideration. I will be gratefull for explicit answers and the references. Thanking you. ANANT D. KULKARNI Ph.D. Student From chemistry-request@server.ccl.net Thu Apr 27 11:00:57 2000 Received: from rzumail2.unizh.ch (rzumail2.unizh.ch [130.60.128.10]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id LAA19735 for ; Thu, 27 Apr 2000 11:00:54 -0400 Received: from zisgi.unizh.ch (zisgi.unizh.ch [130.60.19.17]) by rzumail2.unizh.ch (8.9.3/8.9.3/06) with ESMTP id RAA13364 for ; Thu, 27 Apr 2000 17:00:36 +0200 (MET DST) Date: Thu, 27 Apr 2000 17:00:36 +0200 From: "Dr. Peter Burger" To: CHEMISTRY@ccl.net Subject: CCL:temp. dependence of dielectric constant Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Dear CCLers, though I know that this is off-topic, I wonder whether someone could point me towards a reference, where a formula for the temperature dependence of the dielectric constant, eps(T) of a solvent has been derived. From what I have found so far it seems to be either eps(T) = constant x exp(-T/constant1) or eps(T)= constant/T - the latter I have found in a paper where solvent properties were simulated by Monte Carlo molecular dynamics - unfortunately they did not give a reference. Is statistical thermodynamics a good point to start? Any comment is highly appreciated Peter ----------------------------------------------- Peter Burger Anorg.-chem. Institut Universitaet Zuerich 8057 Zuerich Switzerland chburger@aci.unizh.ch From chemistry-request@server.ccl.net Thu Apr 27 11:03:13 2000 Received: from fisquim.fcq.unc.edu.ar (root@fisquim.fcq.unc.edu.ar [200.16.18.35]) by server.ccl.net (8.8.7/8.8.7) with ESMTP id LAA19732 for ; Thu, 27 Apr 2000 11:00:47 -0400 Received: from Adriana.fisquim.fcq.unc.edu.ar ([200.16.18.152]) by fisquim.fcq.unc.edu.ar (8.8.7/8.8.7) with SMTP id MAA21334 for ; Thu, 27 Apr 2000 12:08:39 -0300 Date: Thu, 27 Apr 2000 12:08:39 -0300 Message-Id: <200004271508.MAA21334@fisquim.fcq.unc.edu.ar> X-Sender: aolleta@fisquim.fcq.unc.edu.ar (Unverified) X-Mailer: Windows Eudora Light Version 1.5.2 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: Computational Chemistry Mailing List From: adriana Hi CCL'ers: I have calculated the activation energies for addition reactions of the oxygen atom in its ground state to halogenated olefins with the Gaussian 98 program by the QST3 method at the following theory levels: UHF/6-31G*, UHF/6-311G**, PMP2/3-21G*, PMP2/3-21G**, MP4SDQ/3-21G**, CCD/3-21G**, PMP2/6-31G** and MP4D/6-311G**. The results showed that: - the barrier values are overestimated by using the levels UHF/6-31G*, UHF/6-311G**, MP4SDQ/3-21G** and CCD/3-21G**, - at the levels PMP2/6-31G** and MP4D/6-311G**, the barriers are underestimated and even negative which is known to be impossible. - However, the activation energies calculated with PMP2/3-21G* and PMP2/3-21G** are within experimental error. I would like to know why the more sophisticated methods give erroneous values? Thank you very much in advance for your answers which I will eventually summarize.