Talk:Organic:whogotthefunk

Q1. The energy values are all correct as is the suggestion that the dimerisation occurs under kinetic control. Bending strain refers to the deviation from ideal bond angles and is clearly the major difference between 3 and 4. The most stable hydrogenated compound is 4 and this is the one that is formed, but this doesn’t necessarily mean the hydrogenation is under thermodynamic control: the thermodynamic product could also be the kinetic product.

Q2. The energy for the first compound is correct, but the 2nd are a little high. The discussion with regard to reaction selectivity is correct. A side point: the reactions here are not stereospecific, they are stereoselective; this means that one product isomer is favoured over the other. A stereospecific reaction only forms one isomer (it would be impossible to get the other) e.g. an SN2 reaction is stereospecific, because you always invert at the centre where you substitute.

Q3. Your calculations are good as is the discussion of the minimisation process. It might have been better to calculate the chair conformation for both atropisomers as well as the boat and twist-boat before deciding which was most stable. Although the cyclohexane unit is the most important part of the molecule with regard to optimising the energy with MM2, It is also possible to further optimise the rest of the molecule to get a lower energy. The definition of a hyperstable alkene is correct.

Q4. The calculations and MO diagrams look fine. The double bond under the C-Cl bond is in fact more NUCLEOPHILIC, not electrophilic as shown by its higher orbital distribution in the HOMO. Your stretching values are good and the reasoning for the change in frequency is about right, although it may have been worth discussing which orbitals are involved that cause the C-Cl to be weakened when the double bond is in place – it is a donation into the C-Cl sigma* orbital that is important here.

MINI PROJECT. With regard to the “coupling” in the experimental 13C NMR, I’m not entirely sure what you mean. It is not possible to see 13C-13C coupling because since 13C only makes up a small proportion of the total carbon content, only very small amounts of compound will have two 13C carbons present that can couple and hence this is not seen in the spectrum. Additionally, you won see 1H-13C coupling as 13C NMR is usually measured decoupled to simplify things. For the presentation of the data, it would have been useful to see a table comparing the literature and experimental values, and the error you found between the two – this is often represented as a bar graph in literature examples displaying the error for each carbon to clearly show which are the least accurately calculated resonances. Other than this, the compound you chose was a good choice in that it was inflexible, but it is a shame that the data is too close for both isomers.