© 1999 Rainer Glaser. All rights reserved.
The University of Missouri at Columbia
Chemistry 412, Computational Organic Chemistry, FS99

Instructions Organizing and Topic Assignments
of the Specific Exercises Related to

Theoretical Level Dependency

"Theoretical Level Dependency" always is a central issue in any theoretical discussion. One needs to know how well a given model performs. The theoretical level dependency of different properties can be quite different. Many methods give good geometries, for example, while there are fewer methods that provide accurate dipole moments. So, we will take a look at "Theoretical Level Dependency" for a few cases that exemplify selected issues well. A few topics covered in the past ar available for study are listed below. A topic can be claimed either by an individual student or by a group of students. If you have a preference for a certain topic, do let me know as soon as possible.

Here is what you should do. Carry out the computations using Gaussian94 on Shiva. Tabulate your results so that the parameters show up on the horizontal and the theoretical levels on the vertical. We will be adding data obtained at many theoretical levels as we go along in the course. Eventually, we will produce html files of your tables and post them on the web. You can include as many parameters in the tables as you like. Start with the key parameter I am asking for (e.g. the dipole moment of CO, the rotational barrier in formamide, ...) and then add parameters that you think are of interest as well. Feel free to talk to me if you need some feedback. Of course, it would not hurt to run a CAS search on your topic and learn what others have thought about the issue before.

I will update this file as we go along specifying additional levels at which you should examine the problem. Of course, do not feel limited by my requests! You can do as many theoretical levels as you like (just do not crash the system).

Update 10/11/99: Carry out calculations at the levels RHF/STO-3G, RHF/3-21G, RHF/6-31G, RHF/6-31G* and RHF/6-31G**. In all cases, optimize the structures using the keyword opt=z-matrix. In addition, you should use the keyword GFP (stands for Gaussian Function Printout) in these calculations so that you get some idea about the magnitudes of the exponents. From now on, also please keep track of the time used for the calculation. Record the computation time given at the bottom of the output file.

Possible Topics and Assignments

Topic #1: Acetonitrile and its isomer, MeCN and MeNC.
Assignment: OPEN
These highly polar molecules are very different bonding situations. It will be of interest to see how well theory can reproduce the isomer preference energy. Keep an eye also on the lengths of the multiple bond and the dipole moments.
Topic #2: The rotational barrier in formamide.
Assignment: OPEN
A classical case. The barrier that governs the conformations of peptides. You will need to compute the equilibrium structure (which may not be planar at the amino-group) and two transition state structures (the ones with a pyramidal NH2 group that have the N-lone pair either syn or anti with the C=O bond) at each level.
Topic #3: Comparison of 1,3-pentadiene and 1,4-pentadiene.
Assignment: OPEN
One is conjugated and one is not. Does the theoretical model account for this difference well?
Topic #4: Activation barrier for nitrogen inversion in ammonia..
Assignment: OPEN
This assignment requires the computation of ammonia in C3v and D3h symmetry at every level.
Topic #5: Activation barrier for H-abstraction reaction from methane by fluoride ion..
Assignment: OPEN
This assignment requires the computation of methane in Td, of fluoride ion, and of the transition state structure in C3v symmetry at every level.