Talk:Mod:SabrinaThree

Cope: Clear introduction and initial conformational search. Even after reoptimisation with DFT, gauche 3 is still relatively low in energy in comparison to some anti conformers – any ideas why?

Good description of imaginary frequencies in IR analysis.

Thermochemistry all looks fine

TS also look fine, and good descriptions of the methods used. However, could do with a little more comparison of geometries between the methods – do they come up with identical results?

QST2 looks fine, and good to see all 3 extended methods investigated for the IRC. Animations of the reaction path are also impressive. However – if the boat IRC calculating force constants always ran for 51 steps, did it really run to completion or did it simply run out of steps?

Activation energy for chair using DFT is a little off – is this a typo? The entry for ‘activation energy’ in Hartree doesn’t seem to be calculated correctly. Also, calculated at 0K (in which case we should use E + ZPE) or 298K (E + thermal energy)?

Diels Alder: Introduction and initial MOs all look good. Perhaps talk about allowed and forbidden reactions more though when we’re talking about orbital symmetry.

For TS MOs: “with DFT being known to be more accurate and therefore reliable” – in this case we should probably rely on our inference – what would we expect the TS HOMO to look like based on the frontier orbitals that are interacting here?

Good to see the IRC (I wouldn’t worry too much about the automated way it selects which reaction direction is ‘forward’ and which ‘back’).

Exo/endo – “The anomolous molecular orbital is the HOMO of maleic anhydride when optimised using the AM1 method.” – again, really? Or is the DFT the anomalous orbital? The HOMO and HOMO-1 are very close in energy and easily switched, so what would we expect from frontier MO theory here?

Definitely plausible that sterics play a bigger role here in the selectivity, particularly given the MO evidence you have. Good to see that you’ve backed this up with some comparison of the geometries too.

Activation energies seem sensible.

Overall: Generally very good, a few tweaks on presentation (Better Table/Figure numbering etc) would be an easy way to improve a little, but presentation is good overall anyway. Try to relate your findings more to what you’d expect to see though – some more references would help here, either to other literature results or to the theory behind (for example) secondary orbital overlap. This would help you when you’re describing the actual process of forming the TS and make this section clearer I think.