Jump to content

Talk:Organic:Victoria2

From ChemWiki

Q1 Your energies are all correct. You correctly identified that the dimerisation reaction must be under kinetic control; this is due to a secondary orbital effect stabilising the transition state that leads to the endo product. The key role played by bending strain in contributing to the energies of 3 and 4 is explained well.

Q2. The energies are a little off for the 2nd optimisation, but otherwise fine. All of your reasoning with regard to the selectivity of reaction is spot on and the minimisation process is well presented. In the mechanism I imagine the product you form is the amine, i.e. the curly arrows push the negative charge onto N+, rather than forming an enolate. As a side point: “minima” is the plural of minimum – so you can find local minima, but it should be global minimum, as there is only one.

Q3. You are correct to identify the conformations of the cyclohexane unit as being the most important part of the optimisation process, but the overall objective was to look at the difference between having the CO group up or down. Since those are the arrangements in the two atropisomers of the taxol intermediate. The definition of a hyperstable alkene is good.

Q4. The calculations are good and you got the right stretches. The discussion surrounding the weakening of the C-Cl bond is good and I thought that the inclusion of the diagram showing the pi and sigma* orbitals was a good idea to illustrate the point. You correctly identified the double bond syn to the Cl atom as the most nucleophilic.

MINI PROJECT. The molecule was a good choice as you showed with the good fit to the experimental data. It is good that you worked out the error in your NMR and IR data, but when finding the average error you need to find the modulus of the errors involved (i.e. you can’t have negative numbers) because otherwise positive and negative values will cancel out to some extent. It may also have been interesting to compare the error in calculated NMR shifts of both isomers to the experimental data for ONE isomer. This would show, hopefully, that the data for the isomer that you think is correct is a closer fit than the other possibility – this is how data is normally analysed in literature examples of calculated NMR. The IR data is often a little less accurate than the NMR (although as you showed the percentage difference shows that the fit is better than it initially looks) because the IR spectrum is usually calculated for the compound in the gas phase and so doesn’t take into account interactions between molecules in the liquid or solid phase, which is probably the experimental situation.