Talk:Mod:jhb79574592
1.2.1. Good energies for all four cpds. Presentation is nice. NB: It is not possible to compare the energies of the starting materials and products of the reaction, only to compare isomers of the products. Bending contribution specifically corresponds to deviation from ideal bond angles: Bending contribution is greater for the hydrog. product with the double bond on the 6-ring, as in this bridged system the deviation from the ideal bond angles for a double bond (e.g. 120 deg) is worse than if the double bond is in the 5-ring. Again, you can’t really compare the energies of the starting materials and products of the hydrogenation, but I agree that the rigidity of the system would make the starting materials less stable. These ring systems can get close to ideal bond angles for sp3 carbon but not so close for sp2.
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1.2.2 Energies are all good and the CO group dihedral angle is correct for lowest energy conformation in both cases. The reason for the stereoselectivity in the first case is indeed due to coordination of the nucleophile to the carbonyl group. In the second case, you were correct in the first place: the effect is due to repulsion between the carbonyl oxygen and the incoming nucleophile.
I don’t think the reaction will go via enolate intermediates; the driving force comes from relief of the charge on the nitrogen atom. The magnesium can still coordinate to the CO oxygen so I think the reaction will proceed from the second item on your mechanism going straight to the product, pushing the bonds around the ring and onto N+. I think you may have confused NOE with something else. The NOE relates to the magnetic influence of one nucleus on another that is close through space and is used to probe molecular structure by NMR.
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1.2.3. The energy for the CO-up isomer is correct, but the CO-down isomer is a little high (this is in fact the more stable of the two). The jmols reported both display the 6-ring in the chair conformation, and as you speculate one of the two should be twist-boat. Definition of a hyperstable alkene is good, but MM2 can’t be used to directly compare the energies of alkene and hydrogenised analogue.
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1.2.4. The energies obtained are good (slightly high in one instance, probably due to stabilisation via the wrong H-bond…more than one is possible). Reasoning for fast hydrolysis is correct, but the explanation for the difference in the two systems isn’t so straight forward. It appears that all forms of the starting material could react (i.e. the groups are close enough and have the right angle of approach; this is opposed to what is reported in the paper). Thus a full explanation cannot be accounted for by the conformations of the starting materials.
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1.2.5. Good ideas: may have benefitted from a tabulated comparison of the stretching energies of the exo and endo bonds and that of the monohydrogenated compound.
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MP It wasn’t necessary to do two mini-projects! Both projects are well investigated and the data is well analysed, although it would have been good to see the differences between calculated and reported chemical shifts tabulated.