Talk:Mod.MAP107

Q1: The energy values are all good, and the dimerisation is correctly defined as being under kinetic control – this is due to a secondary orbital interaction that stabilises the transition state leading to the endo product. The contributions to energy for the hydrogenation products are well analysed – analysis of the bond angles is the best way to find the reason for bending strain. The hydrogenation will likely be carried out with a transition metal catalyst. Kinetic control may be important if one double bond is considerably more accessible to coordination than the other and thermodynamic control could be operating if the intermediates on the catalytic cycle are interconvertible.

Q2: The calculations are good as is the discussion of the steps you took to optimise the energies. The selectivity is well explained in both cases. Note that stereoselective and stereochemistry etc are written as single words. The reason that Mg cannot be included in the calculations is that MM2 does not have any parameters for Mg; this could be remedied by editing the parameters manually.

Q3: The calculations are again fine, it is good that you have analysed the various strain types present, but it would be nice to see some of the different conformations you discovered along the way to deciding which is the global minimum.The definition of hyperstable alkenes is good as is the demonstration using MM2 of the difference in strain between the alkane and alkene, but bridgehead alkenes are not necessarily inherently hyperstable themselves (e.g. some bridgehead alkenes are so unstable you can’t make them – Bredt’s rule).

Q4: The MOs are presented really well and the discussion is great. The frequency in wavenumbers that you get for the C-Cl stretch of the hydrogenated compound should be lower than the case of the diene. A weaker, longer bond is associated with a lower wavenumber as this is proportional to the amount of energy required to effect the stretching and overcome the bond’s stiffness. I think it is possible that the comparative C-Cl stretch you were looking for in the second case would have been at 500-600 wavenumbers. The discussion about the influence of the anti double bond is good and overall this question is well answered with an appropriate level of detail. You should be careful when naming your compound as this is not a dichlorocarbene itself, it is a molecule that reactions regioselectively WITH dichlorocarbene.

MINI PROJECT: This mini-project is excellent. You went beyond what was expected for the stereoselectivity discussion, and still completed the other calculations. It is a shame that the spectroscopic detail was not capable of distinguishing between the isomers, you did not discuss how the authors distinguished the compounds other than to say that they have different optical rotations – I think in this case the workers probably matched their data to existing data of someone else who actually went to the trouble of doing a full assignment and proof of structure. It is also often the case that for such catalytic processes, the authors will show that they have a certain selectivity in one case and then assume it is the same for the rest of the examples (which is actually a pretty reasonable thing to do). The analysis of the errors in your NMR and IR calculations was very good as well and you have given some good suggestions as to why certain calculated peaks are slightly out. Overall, the errors seem to be quite low, so this compound was a good choice in that respect. Again you need to be slightly careful with some of the naming: the iminium species formed is an intermediate not a transition state, the initial energies you report are for the products not the transition states but I think that is what you meant. Overall it was a well presented, detailed discussion of the reaction in question.