From owner-chemistry:~at~:ccl.net Sun Dec 10 01:24:01 2017 From: "Ahmed S. Abo Dena ahmed_said5899.:.yahoo.com" To: CCL Subject: CCL:G: Enantiomeric excess via Conformational analysis Message-Id: <-53086-171210001257-22486-0Etum3y5MAX41u1rXSmW1A*|*server.ccl.net> X-Original-From: "Ahmed S. Abo Dena" Content-Type: multipart/alternative; boundary="----=_Part_2064541_119716474.1512882768663" Date: Sun, 10 Dec 2017 05:12:48 +0000 (UTC) MIME-Version: 1.0 Sent to CCL by: "Ahmed S. Abo Dena" [ahmed_said5899{}yahoo.com] ------=_Part_2064541_119716474.1512882768663 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hello Mohamed, Hope you all the success in your work. In my opinion, the energy obtained f= rom conformationl analysis is not as accurate as that obtained from quantum= mechanical calculations because it depends on molecular mechanics. Gaussia= n 09 or similar softwares can predict the energy of your molecules with hig= h accuracy. Accordingly, I recommend using the transition state (ts) calcul= ations. Another idea is to use the three methods (ts, conformational analys= is and Boltzmann population) and see if they end up with the same results. Regards,Ahmed Sent from Yahoo Mail on Android=20 =20 On Sun, Dec 10, 2017 at 7:02 AM, Mohamed E. A. Safy m.safy*o*compchem.net= wrote: =20 Sent to CCL by: "Mohamed E. A. Safy" [m.safy{=3D}compchem.net] Dear CCL community In one of our running projects, we are working in a collaboration with=20 organic chemists. They asked us to perform calculations on enantiomeric=20 excess of a molecule. According to the transition state theory, the calculations should be run on= =20 the transition states to predict the enantiomeric excess. This is because= =20 the R- and S- enantiomers are equal in energy. Indeed, if we searched for the most stable conformation for each of R- and= =20 S-enantiomers using conformational analysis technique, we will find that=20 the most stable conformation of R- and S- enantiomers are not identical in= =20 energy. Moreover, if we used the most stable energy in Boltzmann=20 population, we will get %population in agreement with %ee (enantiomer=20 excess). So, we were wondering if this approach of conformational analysis followed= =20 by Boltzmann calculation would be a good approach to predict the %ee? If=20 yes, so is there any reference would support our approach?=20 Any comment would be highly appreciated. Have a nice day M. Safy -=3D This is automatically added to each message by the mailing script =3D-=C2=A0 =C2=A0 =C2=A0=C2=A0 =C2=A0 =C2=A0Subscribe/Unsubscribe:=20 =C2=A0 =C2=A0 =C2=A0Job: http://www.ccl.net/jobs=20=C2=A0 =C2=A0 =C2=A0=20 ------=_Part_2064541_119716474.1512882768663 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hello Mohamed,

Hope you all the suc= cess in your work. In my opinion, the energy obtained from conformationl an= alysis is not as accurate as that obtained from quantum mechanical calculat= ions because it depends on molecular mechanics. Gaussian 09 or similar soft= wares can predict the energy of your molecules with high accuracy. Accordin= gly, I recommend using the transition state (ts) calculations. Another idea= is to use the three methods (ts, conformational analysis and Boltzmann pop= ulation) and see if they end up with the same results.

Regards,
Ahmed

Sent from Yahoo Mail on Android<= /div>
On Sun, Dec 10, 2017 at 7:02= AM, Mohamed E. A. Safy m.safy*o*compchem.net
<owner-chemistry= **ccl.net> wrote:

Sent to CCL by: "Mohamed E. A. Safy" [m.safy{=3D}compche= m.net]
Dear CCL community
In one of our running projects, we are working in a collaboration with <= br>
organic chemists. They asked us to perform calcul= ations on enantiomeric
excess of a molecule.
=
According to the transition state theory, the calcul= ations should be run on
the transition states to= predict the enantiomeric excess. This is because
the R- and S- enantiomers are equal in energy.
= Indeed, if we searched for the most stable conformation for each of R- and =
S-enantiomers using conformational analysis tech= nique, we will find that
the most stable conform= ation of R- and S- enantiomers are not identical in
energy. Moreover, if we used the most stable energy in Boltzmann
population, we will get %population in agreement with = %ee (enantiomer
excess).
So, we were wondering if this approach of conformational analysis follow= ed
by Boltzmann calculation would be a good appr= oach to predict the %ee? If
yes, so is there any= reference would support our approach?
Any comme= nt would be highly appreciated.
Have a nice day
M. Safy



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