Talk:Module1:organicwm207

Q1: The energy values are all spot on. The dimerisation is indeed under kinetic control, the reason the relevant transition state is relatively lower in energy is due to a beneficial secondary orbital interaction. The various energy contributions are listed, but a comparison of the data would have been better; for the two hydrogenation products, bending strain is the major contribution owing to the relative deviation of the double bonds from the ideal sp2 bond angles. The hydrogenation would probably be carried out using a transition metal catalyst – so kinetic control could come into play if two double bonds are more or less available for coordination, or thermodynamic control could be important if the intermediates on the catalytic cycle are interconvertible.

Q2. The calculation for the first compound is good, as is the explanation for stereoselectivity of the attack by the Grignard reagent. For the second compound, attacked by aniline, the more stable compound has the carbonyl group pointing down relative to the aromatic ring; selectivity is due to the clash between the aniline lone pairs and those on the carbonyl group. Your reasoning for the inability of MM2 to incorporate Mg into a calculation is right; it is in fact possible to add parameters in order to include elements for which there is no information to start with.

Q3: The “down” isomer is in fact the more stable form of the molecule. You should have found that one of the atropisomers prefers to have the 6-ring in a twist-boat conformation. Also, it would have been a good idea to present various conformations and their associated energies in this problem as this would give a good impression of the optimisation work necessary in this problem. The stability of the double bond is not discussed: this is an example of a hyperstable olefin, in which high stability is observed on account of the hydrogenated analogue of the double bond (e.g. the alkane) giving rise to a greater amount of strain relative to the double bond itself.

Q4: It is expected that the most nucleophilic double bond is the one syn to the chlorine. The MOs look a little different to what I would expect, is it possible that the wrong calculation result (on the Chem3D surfaces scroll down menu)? The IR frequencies you have obtained are good, but there is no discussion. For the compound without the double bond anti to the C-Cl bond, the C-Cl bond is strengthened; this is a consequence of that double bond donating some of its electron density into the sigma* orbital of the C-Cl bond. You should be careful when naming compounds: this compound is not dichlorocarbene itself, but rather a compound that can selectively react with dichlorocarbene.