Talk:Mod:fs1309

Q1

• Where are the calculated data for structure 1 and 2?

• "bond angle of a double can no longer" should be double bond".

• You correctly calculated the energies of 3 and 4 using MM2 and identified the Bend energy as the main contributor to the difference in energy. *" According to the bond angle measurement, product 4 has the bond angle of 112°, which is closer to 120° than product 3 does and therefore it’s lower in energy. " What's the corresponding bond angle in 3 then?

Q2

• Wrong energies for 9 and 10. These are clearly not the global minimal. You likely have optimised into a local minimal, a common mistake in computational chemistry. The only way to prevent this is to use your chemical sense to figure out the most likely conformations even before calculation, and then perform optimisation on each of them.

• If you have given me a picture/jmol of your structures, it would have helped. How am I supposed to know what the structures look like?

• You seem to get what hyperstable alkenes are, but did not specify when and where they often happens (more google and reading would have helped!).

• Clearly MM2 and MMFF94 would give different energies because they use different force field parameters. What we're really looking for is whether they give similar difference in energy between 9 and 10? That would decide whether the two methods are comparable or not!

Q3

• I can't possibly see the atoms in your HOMO picture, which is the most important one. There are options in Chem3D to change the display modes, which are also mentioned in the wiki instructions.

• You specified in the table that the MO models are from Gaussian, they look more like from Chem3D to me. Also the instructions did say use MOPAC, in Chem3D.

• You showed some understanding of the interaction between the pi system and the C-Cl sigma bond, but could have been more specific.

• Correct prediction of reactivity, although again could have been much clearer.

• Monohydrogenated product: which structure?

• " The difference between two double stretching frequecnies arise from the stabilizing antiperiplanar interactions, which strengthens the exo double bond, between the C-Cl σ* orbital and the occupied anti filled pi orbital. This makes the endo double bond more reactive and therefore matches the analysis in part 1. " You lost me here. Should have used the syn-anti terminology in the question, or at least structures with numbering.

• Your IR frequencies for the diene are correct. But you don't seem to appreciate what they mean in terms of the stability of the double bonds. Assignments of the frequencies to the two double bond are also missing.

• Analysis of bond lengths would be great for this question.

Q4

• Correct choice on Me group.

• "The MM2 method is used here as it also includes interaction between oxygen lone pairs". I'm not sure that oxygen lone pairs can interact with each other.

• Your optimised structures and energies are wrong. It can clearly be seen that there is no interaction in these structures between the acetyl group and the carbocation.

• Bond lengths and bond angles: what we're really looking for here is the distance between the acetyl and the carbocation and the angle of approach.

Mini project

• I really need to you identify exactly what question you're trying to answer with this calculation here.

• A ChemDraw picture of structure 14 and 15 would certainly help.

• Your table seem to give the same 13C chemical shifts for both 14 and 15 and doesn't provide any data to prove/disprove one diastereomer over the other.

• We know the chemical point of view on the selectivity of the reaction, but the point of the calculation is to prove the outcome, which the data you presented did not.