Talk:Mod:ms mod1

Q1

• “hyperconjucation” should be “hyperconjugation”

• Correct energies for 1 and 2. You correctly identify the torsion energy as the main contributor to the difference, but gave the wrong explanation for it.

• Correct energies for 3 and 4. I think you understand where the difference in bend energies comes from, but you could have been clearer in explaining it. Hydrogenation is almost always under kinetic control (non-reversible!) so indeed one needs to look at the TS, but that’s Module 3.

Q2

• Thorough examination of different conformers.

• Comparison between MMFF94 and MM2, you should have compared the difference in energy between different conformers, calculated by the two methods. Such value is directly comparable between different techniques.

• Decent explanation of ‘hyperstable alkenes”, you chould have also mentioned they often happen at bridgehead position.

Q3

• How did you optimise the structures? How did you calculate your MOs?

• Your MOs look fine, but a mistake was made in labelling them, specifically the LUMO.

• I don’t see the overlapping between the anti pi-bond and the antibonding sigma C-Cl in your MOs.. Here it’s important to say exactly in which MO there is such interaction. Also some comparison of bond lengths between the two C=C bond would help.

• Correct vibrational frequencies. Decent analysis on the changes in C-Cl frequencies.

Q4

• Me group is the correct choice for R.

• Correct PM6 energies for A/A’ and B/B’. You need to tell me if the Jmol structures are from MM2 or PM6. There is inconsistency between A and B, I think one was done with MM2 and the other PM6. A’ and B’ (assuming MM2) are not the global minimal.

• Well spotted that with PM6, A = C, B = D. You should have gone on and given a reason for this.

• I don’t agree with Figure 4. You only have to do a mirror image of D through the horizontal plane to see something quite similar to C. Their difference in energy is quite small.

• You could have used the energy of C/C’ and D/D’ to calculate the ratio of diastereomers in the final product to prove the diastereospecificity. Remember that’s what computational chemistry in organic chemistry is all about: quantitative energy difference -> quantitative determination of selectivity.

• What’s the value for neighbouring group stabilisation energy?

Mini project

• I’m not sure what’s the problem you’re trying to solve with computational techniques.

• Which methods did you used to calculate IR and NMR? Why do you think IR would be informative?

• “The predicted wavenumbers are systematically too high for stretches by around 8%.”. Only the O-H stretch you gave was higher than literature value.

• 4-Bond couplings are possible, and normally in the order of J ~ 1 Hz. So their assumption wasn’t wrong. I’m sure they even have COSY to back it up. The most likely reason why the literature didn’t report the more obvious 3J values is that too many signals are overlapping in a narrow region. A discussion with us on these would have done you very well here.