Talk:Mod:theoreticalreality

Introduction

No general introduction.

Cope rearrangement

Successful optimisations of some conformers - although not all of them. Any physical explanation for their relative energy? Good interpretation of the frequency calculation. TS optimisations successful. “Another interesting result from [the TS optimisations] is the calculations predict that the faster rate of rearrangement will be via chair not boat.” Be careful: in order to predict the faster mechanism (through a Chair or Boat TS), you need to identify the reactant/product that the TS links and calculate their relative energies. You can not conclude without the IRC results. “The optimization has thus show the Cope rearrangement has seen an anti2 conformer go to a gauche2 conformer” Again, be careful: you only have done a FORWARD IRC so you know that the Chair TS leads to the gauche2 conformer product. To identify the reactant, you need to run a BACKWARD IRC.

Diel-Alder cycloaddition

An important point about the TS of butadiene + ethene is that the C(2)-C(12) bond length is longer than that of a normal C-C bond but shorter than 2x vdW(C) radius indicating that the "number of (4q+2)s and (4r)a components is odd" - system is between products and reactants (as would be expected of a TS). What do the two lowest vibrational modes tell you about the curvature of the PES around the TS. Notice how the imaginary mode preserves symmetry while the lowest real mode breaks it, suggesting the reaction is concerted (as confirmed by the IRC).

Conclusion

No overall conclusion. Presentation is good, but there are some questions asked in the exercise that you have not addressed. There are other published calculations on these systems to check against. It's important to do this for calculations to see if any of the effects seen have been explained elsewhere.