Talk:Module1:AYKLeung
Q1. Your calculated energies are correct, but there is no need to report to so many significant figures; you probably found when doing the calculations that the same calculation will generate differences in the last few decimal places from one time to the next, so the error can be roughly gauged. The explanation for kinetic control in the dimerisation reaction is correct and the diagram nicely shows the secondary orbital interaction. For the comparison of energy contributions, bending strain is the major difference between the monohydrogenated compounds and you are right to attribute this type of strain to deviation from ideal bond angles – probably the most important ones to look at are those of the different alkenes.
--
Q2. The approach you took in answering this question was good in describing the different conformations you found and looking particularly at the lowest energy conformation; the molecule of course spends most of its time in this shape so that defines its chemistry. The selectivity matches your dihedral angles and explanation – the reason the aniline attacks anti to the carbonyl group is because the atoms involved are electron rich and the approaching lone pairs repel each other.
--
Q3. The energy values are good and you have correctly said that the down isomer is lowest in energy – For these larger systems it would be better to upload the jmol because there a number of structural features that need to be checked. Hyperstable alkenes are correctly defined – it is the difference in strain between alkene and alkane that is the most important thing (shielding of the alkene isn’t a big part of the phenomenon).
--
Q4. The MOs look good and your reasoning about the nucleophilicity is correct (more density of the HOMO on the syn alkene means it is the most nucleophilic). This greater nucleophilicity relative to the anti double bond is as you suggest due to the stabilisation of the pi electrons of the anti double bond by interaction with the C-Cl antibonding orbital. Spectra is the plural form of spectrum (i.e. spectrum of diene, spectra of diene and monoalkene). The statement that the C-Cl bond is stronger in the monoalkene because interactions from the anti double bond are remove is correct. The reason is that the anti-double bond is donating into the C-Cl sigma* antibonding orbital thus weakening the bond; this is the combination of LUMO+1 and HOMO-1 you mentioned.
--
MP. This is an interesting mini project which seems like a good choice given the similarity to some of the earlier questions in the course. The reason your NMR values don’t match the experimental shifts is that you haven’t chosen a reference on the gaussview panel. If you have a similar inexplicable problem like this in the rest of the course it could simply be due to missing a step in the calculation or analysis so please ask for help! Another thing is that there should be many more than 9 carbon peaks in the spectrum, don’t forget all of the atoms in the aromatic side groups! Some times it can make sense to neglect certain peaks that aren’t really relevant to the problem at hand (i.e they may be far away from the centre of interest) but it isn’t clear that is what you meant.