Talk:Mod:ss7009

Q1

• There's no " mimicking" here, Cp acts as both diene and dienophile.
• Your Jmol for 1 and 2 are for 3 and 4.
• Correct energies for 1 and 2 and analysis of torsion energy.
• Correct energies for 3 and 4 and analysis of bend energy.
• Good appreciation of the 'wrong approach' for part 2

Q2

• " This type of isomerism is especially common in the Taxol precursor " only one compound, so it can't be common.
• Reasonable arguments and analysis of the data, although your structure for 9 isn't yet the lowest energy. But it's close enough.
• "Hyperstable alkenes": you understand the concept, but could have calculated the alkane to compare for the olefin strain.

Q3

• " Therefore, reaction with dichlorocarbene would render the endo double bond more susceptible to electrophilic attack."
• Your LUMO doesn't match your analysis, i.e. anti-bonding orbital of the double bond. Upon examining your Chem3D file, it turns out to be a bad picture. But you should have chosen a better view angle.
• Your vibrational frequencies are significantly off, presumably due to inadequate optimisation.
• No bond length analysis.

Q4

• "The neighbouring group affect is shown in Figure 15" should be " The neighbouring group effect is shown in Figure 15"
• " In addition, the acetyl groups possess oxygens and hydrogens, leading to strong hydrogens bonds." which hydrogen bond?
• " –OME (R=CH3)"
• Correct preference of PM6 over MM2.
• Correct structures for both MM2 and PM6.
• You spotted the energies for A and C are the same using PM6, but surely you must have checked the structure to see if they are identical?
• "A and B are more reactive than A’ and B’", wrong, A and B are more stable than A' and B'.

Mini project

• No defined question!
• your comparison between experimental data and calculated data is very difficult to follow, especially when only one set of experimental data was compared. Are the assignment included in the literature? Did you have to assign the individual carbon chemical shifts yourself?
• Correct spotting of the C4 which will have the most difference in chemical shift between the two structures. Again, this important point should have been made much more obvious. I had to hunt for it.
• Most argument on the selectivity is invalid here. One will to consider the transition states from the Crigee intermediates, which is beyond the scope of the techniques available to you.