From owner-chemistry /at\ccl.net Tue Sep 25 10:01:01 2012 From: "Mauro Barbosa de Amorim maurobdeamorim-#-gmail.com" To: CCL Subject: CCL:G: SN1 reaction Message-Id: <-47661-120925092827-9447-eVSsykVV6fwoYB7zBlM3Ug[a]server.ccl.net> X-Original-From: Mauro Barbosa de Amorim Content-Type: multipart/alternative; boundary=f46d04083a8bce10ff04ca86ad3f Date: Tue, 25 Sep 2012 10:28:17 -0300 MIME-Version: 1.0 Sent to CCL by: Mauro Barbosa de Amorim [maurobdeamorim|gmail.com] --f46d04083a8bce10ff04ca86ad3f Content-Type: text/plain; charset=ISO-8859-1 Dear Nguyen, Unimolecular reactions, implicit in terms E1 and SN1, pass through unimolecular transitions states, involving just the substrate molecule, t-butyl chloride. So, we cannot simulate their transition states using both the nucleophile or base (OH-) and the substrate (t-BuCl). The first step of these reactions would be the Cl-C(CH3)3 bond breaking, followed, as a second step, by the attack of OH- as a base on one of the H atoms (in E1 reaction) or as a nucleophile on the cationic carbon (SN1). Otherwise, you may want to study the bimolecular processes (E2 and SN2), which occur in just one step. In this case, you should direct the attack of the anioic species (OH-) to the central carbon (SN2) or to one os the methyl hydrogens (E2) (that are statistically more prone to attack: 9 to 1, justifying the E2 preference in high OH- conentrations). You should also consider that OH- is more basic than nucleophilic, favoring E2 reactions. My best regards from a sunny Rio. Mauro 2012/9/25 Nguyen Minh Ly nguyenminhly2209*|*yahoo.com < owner-chemistry[]ccl.net> > > Sent to CCL by: "Nguyen Minh Ly" [nguyenminhly2209,yahoo.com] > I have a problem to discuss. I survey the SN1 reaction of tert-butyl > chloride > and OH- by: > 1 / Optimization of structures with Gaussian > 2 / Optimize to find the transition state in the first stage of the SN1 > reaction (using QST2 keyword) > > As we all know, this reaction depends on the concentration of OH-. If > concentration of OH- is low (dilute solution), the reaction will occur > SN1. If > concentration of OH- is high (special solution), the reaction will occur > E1. > > But in GaussView, when I optimized to find the transition state in the > first > stage of the SN1 reaction, I can only draw a molecule C4H9Cl and a OH- in > Reactants window, a molecule C4H9OH and a Cl- in products window. This > means > that the rate of C4H9Cl and OH- concentration in the solution was 1:1 > (corresponding to the high concentration of OH-). So E1 reaction will > occur! > > But I want to find the transition state in the first stage of the SN1 > reaction. > How can do this ? > > Please help me > Thank you> > > --f46d04083a8bce10ff04ca86ad3f Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Dear Nguyen,

Unimolecular reactions, implicit in terms E= 1 and SN1, pass through unimolecular transitions states, involving just the= substrate molecule, t-butyl chloride. So, we cannot simulate their transit= ion states using both the nucleophile or base (OH-) and the substrate (t-Bu= Cl). The first step of these reactions would be the Cl-C(CH3)3 bond breakin= g, followed, as a second step, by the attack of OH- as a base on one of the= H atoms (in E1 reaction) or as a nucleophile on the cationic carbon (SN1).= Otherwise, you may want to study the bimolecular processes (E2 and SN2), w= hich occur in just one step. In this case, you should direct the attack of = the anioic species (OH-) to the central carbon (SN2) or to one os the methy= l hydrogens (E2) (that are statistically more prone to attack: 9 to 1, just= ifying the E2 preference in high OH- conentrations). You should also consid= er that OH- is more basic than nucleophilic, favoring E2 reactions.

My best regards from a sunny Rio.

<= div>Mauro

2012/9/25 Nguyen Minh Ly nguyen= minhly2209*|*yahoo.com &= lt;owner-chemi= stry[]ccl.net>

Sent to CCL by: "Nguyen Minh Ly" [nguyenminhly2209,yahoo.com]
I have a problem to discuss. I survey the SN1 reaction of tert-butyl chlori= de
and OH- by:
1 / Optimization of structures with Gaussian
2 / Optimize to find the transition state in the first stage of the SN1
reaction (using QST2 keyword)

As we all know, this reaction depends on the concentration of OH-. If
concentration of OH- is low (dilute solution), the reaction will occur SN1.= If
concentration of OH- is high (special solution), the reaction will occur E1= .

But in GaussView, when I optimized to find the transition state in the firs= t
stage of the SN1 reaction, I can only draw a molecule C4H9Cl and a OH- in Reactants window, a molecule C4H9OH and a Cl- in products window. This mean= s
that the rate of C4H9Cl and OH- concentration in the solution was 1:1
(corresponding to the high concentration of OH-). So E1 reaction will occur= !

But I want to find the transition state in the first stage of the SN1 react= ion.
How can do this ?

Please help me
Thank you



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