From owner-chemistry@ccl.net Fri May 3 00:50:30 1996 Received: from bedrock.ccl.net for owner-chemistry@ccl.net by www.ccl.net (8.7.1/950822.1) id AAA15633; Fri, 3 May 1996 00:43:35 -0400 (EDT) Received: from LV.Levels.UniSA.Edu.Au for CTARG@Levels.UniSA.Edu.Au by bedrock.ccl.net (8.7.1/950822.1) id AAA22223; Fri, 3 May 1996 00:43:32 -0400 (EDT) From: Received: from Levels.UniSA.Edu.Au by Levels.UniSA.Edu.Au (PMDF V5.0-4 #9510) id <01I49SRTHITS9VURBD@Levels.UniSA.Edu.Au> for chemistry@ccl.net; Fri, 03 May 1996 14:13:28 +0930 Date: Fri, 03 May 1996 14:13:28 +0930 Subject: Free Energy of Aluminium Hydroxide species. To: chemistry@ccl.net Message-id: <01I49SRTILEQ9VURBD@Levels.UniSA.Edu.Au> X-VMS-To: IN%"chemistry@ccl.net" MIME-version: 1.0 Content-type: TEXT/PLAIN; CHARSET=US-ASCII Content-transfer-encoding: 7BIT Hi, I recently completed a study of the heats of formation of Al containing hdyroxide species. The program I used was MOPAC with AM1 and PM3. Is it possible to calculate or estimate the Gibbs Free Energy of these speices using this or any other easily available program. Thanks Andrea From jgano@UOFT02.UTOLEDO.EDU Fri May 3 10:50:35 1996 Received: from UOFT02.UTOLEDO.EDU for jgano@UOFT02.UTOLEDO.EDU by www.ccl.net (8.7.1/950822.1) id JAA19056; Fri, 3 May 1996 09:52:09 -0400 (EDT) Received: from [131.183.61.24] ("port 1442"@macgano.chem.utoledo.edu) by UOFT02.UTOLEDO.EDU (PMDF V5.0-5 #9050) id <01I49JMR3DAG00IS1G@UOFT02.UTOLEDO.EDU> for chemistry@www.ccl.net; Fri, 03 May 1996 09:52:12 -0500 (EST) Date: Fri, 03 May 1996 09:52:14 -0600 From: jgano@UOFT02.UTOLEDO.EDU (Jim Gano) Subject: HOCQUET's cyclohexadiene - good pedagogical example To: chemistry@www.ccl.net Message-id: MIME-version: 1.0 Content-type: text/plain; charset="iso-8859-1" Content-transfer-encoding: quoted-printable We had occasion to look at the 1,3-cyclohexadiene problem with AM1 mentioned by Alexandre HOCQUET. It is really interesting and a fine pedagocgical example for students. HOCQUET's conclusion that AM1 gives the wrong conformation, the planar conformation, is not true. However, this is a commonly observed result. The calculation EASILY FINDS THE WRONG CONFORMATION. The wrong conformation is not an energy minimum but rather a maximum at the transition state. That is what makes it so interesting. This is nicely evident by calculating and viewing the IR spectrum, using for example the CAChe system. The IR spectrum of the planar structure contains an absorption at a NEGATIVE frequency. Inspection of the nature of the vibration indicates the distortion necessary to find the proper nonplanar conformation which is lower in energy. >Dear CCLers and Hyperchemers, > >In their molecular mechanics principles review (J. Chem. Ed. , 59, 269-274, >1982) Boyd and Lipkowitz present the conformations of cyclohexa-1,4-diene a= s >an example of supremacy of molecular mechanics upon hand held molecular >models : the dreiding model predicts boat geometry whereas molecular >mechanics calculate it planar. >I do believe that this example is demonstrative, presenting molecular >mechanics to students as a sophisticated hand held model. >Unfortunately, as i tried to minimize cyclohexa-1,4-diene with the MM+ forc= e >field provided by Hyperchem, the results show that the minimum (9.10 >kcal.mol-1) corresponds to a torsion angle between 1,2,3 and 4 carbons of >26=B0, in a boat conformation. The constrained planar structure corresponds= to >9.73 kcal.mol-1 and goes back to the former conformation when constrain is >removed. >Besides, An AM1 semiempirical calculation does find the minimum to be plana= r. >So my questions are : >Does the MM+ forcefield, or the parameters provided in Hyperchem, lack the >accuracy needed to perform this calculation ? >Does any references about molecular mechanics calculations of this molecule >exist ? >Does anybody know the references about calculations, Xray and NMR results >that Boyd and Lipkowitz cite with no references (or, to be honnest, the >reference cited was "in press" : Lipkowitz et al. in J. Org. Chem.) ? >Am i doing something wrong ? > >Thanks in advance for any answers (if somebody is interested, i will >summarize the answers) > >Alexandre Hocquet > >Laboratoire de Chimie Analytique >ESPCI >10, Rue Vauquelin >75231 Paris Cedex 05 >France > >tel : 33 1 40794420 >fax : 33 1 40794425 >email : ahocquet@micronet.fr >ou hocquet@cas.espci.fr >ou hocquet@ens-cachan.fr > > > >--- >Administrivia: This message is automatically appended by the mail exploder: >CHEMISTRY@www.ccl.net: Everybody | CHEMISTRY-REQUEST@www.ccl.net: Coordinat= or >MAILSERV@www.ccl.net: HELP CHEMISTRY or HELP SEARCH | Gopher: www.ccl.net 7= 3 >Anon. ftp: www.ccl.net | CHEMISTRY-SEARCH@www.ccl.net -- archive search > Web: http://www.ccl.net/chemistry.html >--- James E. Gano, Director Instrumentation Center in Arts and Sciences Bowman-Oddy Laboratories University of Toledo Toledo, Ohio 43606 Instrumentation Center : http://www.icenter.utoledo.edu Department of Chemistry: http://www.chem.utoledo.edu 419-530-7847 (419-530-2104) 419-530-4033 (FAX)