Talk:Mod:LS1109

Q1

• Spot on energies of 1, 2, 3 and 4.

• Good and well-detailed analysis on the difference in energy between 1 and 2.

• Very good analysis for comparison between 3 and 4. Incidently, hydrogenation are often under kinetic control (irreversible) and so the whole analysis using product is wrong. Nevertheless, it makes good story!

Q2

• I'm happy with the explanation of atropisomerism.

• Structures 9 and 10 and their energies are correct.

• You can still use the relative difference in energy to compare the results of MM2 and MMFF94.

• Very good account of the hyperstability of the double bond.

Q3

• You seem to have the right optimised structure and MOs.

• Very good analysis, especially the bit on HOMO-1 which most people ignore.

• Then you make a mistake in talking about monohydrated product, instead of monohydrogenated product.

• Calculated IR frequencies are good.

Q4

• Good account for the choice of Me group.

• I'm not so sure about the conjugation in acetyl group. Nevertheless, MOPAC certainly trump MM when it comes to neighbouring group participation, with one big flaw.

• Very careful optimisation of A and B.

• Correct identification of the dipole energy as the main difference.

• What you haven't identified is that with PM6, A = C and B = D. PM6 can handle bonding changes while MM2 cannot. Consequently, it goes straight to the stable intermediate if the orientation of the Ac group is right.

• You also should have calculated the stabilisation energy from neighbouring group participation.

Mini project

• "the unsymetric nature" should be "the asymmetric nature"

• Numbering of compound 11 and 12 could have been better for comparison (similar numbering system would have helped!)

• You've shown you can do 13C NMR calculation, correct the obtained numbers and compare them with literature value. However, I think the question wasn't very well defined and so was the answer. Assuming you did a new reaction with different R group, how would you tell which one is the product? Simple analysis of the two key C's: C4 and C5 in 11 and C1 and C9 in 12 would provide the answer.

• Karplus equation would be no good for 3-4 member rings.

• Nice display of IR vibrations, but then again we don't expect these to be sufficiently accurate for the job of differentiating diastereoisomers.

• Nice conclusions at the end.