User talk:Ds2909

Q1

• Correct energies for 1 and 2. Reasonable explanation of the endo rule and the torsional strain, although you could have been a little bit more specific as to which part of the molecule 2 suffers from this.

• I would hazard a guess that you have the wrong structure for 3.

• You correctly identified bending energy as the difference between 3 and 4, but your argument on the bicyclic structure doesn’t hold, as the bicyclic structure is present in both 3 and 4. In addition, the picture displaying the bond angle is from hydrogenation product of 1, not 2.

Q2

• “compound 10[ref]”

• Good explanation of atropisomerism in structure 9 and 10.

• Correct minimum energies 9 and 10. Well spotted difference in bending energy. You also put in the effort to read the original paper.

• Very good explanation of the hyperstability of the alkene.

• Unfortunately you totally forgot about the MMFF94 question, although you did the DFT calculation. It would have been nice to see side-by-side comparison between the two structures of the exo (what does this means? Please try to use numbering to avoid confusion!) isomer in Jmol format.

Q3

• Correct MOs. But you should learn the option to display translucent MOs in Chem3D. You’ll need it for later modules.

• OK explanation of MOs interaction. You should have been more explicit in stating the selectivity in reaction with carbene. One key piece of information on bond strength is the bond length. Examine it and you’ll have concrete proof, rather than the MOs which may just be figments of our imagination.

• Correct IR frequencies and analysis. Again, a discussion of the bond lengths would have been even better.

Q4

• Correct choice of Me group. Good assessment of PM6 and MM2.

• Your A’ structure is wrong, the acetyl group is nowhere near the carbocation. B and B’ are better in terms of the acetyl group orientation, but are still not the minima in energy. Hint: the other group and also assist in stabilising the positive charge in MM2. PM6 is much better at finding the minima as it gives better account of the secondary orbital interactions.

• “the MM6/MOPAC heat of formation” should be “the PM6/MOPAC heat of formation”

• Jmol structures of A/A’ and B/B’ from PM6 would be very interesting here. Notice that with PM6, A = C, B = D. They are not different structures, because PM6 doesn’t localise electrons but treat the whole molecule as one unit, it automatically move electron around for the lowest possible energy. MM2 can’t do this. You do have the correct bond distances though.

• Your C/C’ are not yet the lowest in energy, D/D’ seem to be.

• Decent account of the diastereospecificity.

Mini project

• “Optical Rotatino, and 3H coupling constanst” should be “optical rotation, and 3J-H coupling constants”

• “an equatorial position[ref]”

• Have your chemical shifts been corrected, or are they straight from Gaussian?

• Good use of selective 13C shifts in differentiating/indentifying diastereoisomers, not everyone gets this. The difference in C13 and C16 is very interesting.

• Shame about the other mini project, but you certainly put in the effort.