Talk:Mod:parkdara

Q1. The energies you calculated are a little lower than expected, but all of the compounds are correct in terms of relative energy, so I assume you used higher level computation. Since the thermodynamically most stable product is not formed experimentally, the reaction must be under kinetic control. This means that the transition state that leads to the endo product is lower in energy compared to the one that leads to the exo product. The reason for this is in fact due to a stabilising secondary orbital interaction. Bending contributions are indeed the key differences between 3 and 4, but the term bending is defined as the strain due to deviation from ideal bond angles.

Q2. The energies are a little off in both cases. It would be helpful if you were a little clearer with regard to the position of the carbonyl group; you say that it is up or down relative to the neighbouring aromatic group, but this definition is dependent on the orientation of the molecule, so it would be better refer to a diagram. In the case of the Grignard, the carbonyl group directs the nucleophilic attack as you said, but in the other it does the opposite, acting as a steric blocker due to electrostatic repulsion between it and the aniline nucleophile. You should be careful in the other exercises not to miss these questions in the text.

Q3. Your definition of atropisomerism is actually the opposite of atropisomerism, which is the instance of two conformations that CANNOT interconvert, i.e. the switch extremely slowly – often with a measurably half-life. I assume this was a typo, but be careful to reread the wording of your definitions! Are you sure that the data you report for the minimisation is the right way around, the values you get are correct, but are reported for the wrong isomers. The definition of hyperstable alkenes is good.

Q4. Your MO diagrams look good and you correctly identify the most nucleophilic alkene. The IR data is as expected, but you could have discussed the implications of finding higher or lower stretching frequencies: If you have a stretch with a lower wavenumber (e.g. lower in units of cm^-1), it means that the bond is weaker (you may be able to relate this to the bond length) and you could have speculated on the reason for this.

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MINI PROJECT The reason that the NMR data doesn’t match is because you didn’t choose a reference compound! This gives you back your data in comparison to tetramethyl silane (TMS) as calculated by the same method. How did your data for the IR compare to the literature, it would have been better to report your data and then discuss how well it matches the experimental data.