Talk:Mod:PAP0801

Which method did you use for your calculation? This is really important.
“the kinetically more stable product” isn’t correct.
“The derivative does not have a specific stereochemistry because bond rotation is no longer restricted by the presence of C=C double bonds” ???
You studied the wrong structures for 3
The analysis of bend energy is correct.

“Both MM2 force-field and MMFF92 field” should be “Both MM2 force-field and MMFF94 field”
“hyperstable alkenes” question was not dealt with properly. Your explanation was simply too brief.

Your Jmol structures don’t look like they’ve been optimised.
The MOs don’t look symmetrical, due to a software generated error in optimising your structures. But you should have spotted this.
Correct analysis of HOMO and prediction of reactivity.
Your IR frequencies are correct. But you should have comment on the different frequencies for the two double bonds in 12. The bond lengths also deserve mentioning.

“The MM2 force field and MOPAC/PM6 force fields“, PM6 is a quantum mechanics technique and doesn’t have a force field.
In your A’ and B’ Jmols, the OAc group is nowhere near the oxonium. It is actually possible to bring it in, and you should have asked us to show you.
PM6 structures are presumably quite different, and worth showing.
Wrong conclusion on MM2 vs PM6. PM6 actually take the full effect of neighbouring group into account and optimise A straight to C, which is the more stable intermediate.
How do all these link to the observed selectivity? K = epx(-E/RT)?

MM2 is rather inadequate for optimisation in this case. Even a small change in conformation can have large consequences in 13C shifts.
“The MOPAC results show very little difference in the energy of the isomers so it is not a good method to use for the minimisation of energy in this example”, what’s the justification for this?
There is actually a huge difference in 13C NMR of A and B, both in experimental data and calculated data if you focus on the carbons which matter: C1 and C2. Analysis of 13C NMR calculation, especially in cases where one try to differentiate between structures, must focus on the carbons whose environment changes, not all the carbons as that would dilute the difference.
In terms of methodology, you should have compared the two calculated spectra with each experimental spectrum to see if their assignment was correct. Not to compare A and calculated A, B and calculated B.
1H, J coupling constant and IR are all inappropriate in this case, so there’s no point in doing them.