Talk:Sunkiss pl1208 3

Grade A:

Cope Rearrangement: Presentation: Extremely easy to read. All data was tabulated. Good use of Jmol, animations. All figures and tables given clear legends. Good use of file sharing. Overall this report was an excellent read. Results: Generally v.good. Some results for energies given to 3 or 4 d.p. (be careful as 0.0001 Hartree is equivalent to ~0.063kcal/mol!) Optimized all gauche and anti isomers and correctly noted gauche 3 lowest in energy. V.good analysis of why this could be, considering MOs etc. For graph 1 perhaps this would have a greater meaning if it showed the dihedral scan (i.e. the energy of 1,5-hexadiene as you rotate the dihedral angle). Good individual thought given to the lowest energy isomers and the reaction path. Stated ‘Gauche-3 conformer would be the most abundant in the reaction mixture’ – good, although should note its abundance is dependant on temperature. Also ‘the Cope rearrangement is expected to occur via the Anti-conformer 2 due to the correct orbital orientation of the vinyl groups and as it is of a slightly higher energy level (lower energy barrier) making it the most reactive species’, however via this thought process wouldn’t it go through the anti-conformer 3 which is highest in energy? Good thought process to try and rationalize why we are focussing on anti-2 in our further calculations – however is in fact due to when optimized with a higher level of theory, anti 2 is actually slightly lower in energy than the gauche 3 isomer. By definition, activation energy is calculated from the lowest energy/most stable reactant to the transition state. Good understanding you can’t really compare energies between different methods (HF and DFT), they’re calculated on different energy scales. But analysis of the difference in the geometries is v. thorough. Vibrational analysis good – Output from frequency analysis of HF shows only a freq calculation, not freq+opt. What was the input structure for here? Should have been the optimized anti-2 conformer as shown in the section above, which when you look in the output has optimised to a local minimum. V.good investigation of ZPE/thermal contributions at 0K and 298K and understanding of this matter. Boat and chair TS: optimisations explained well and imaginary frequencies given and animated. IRC carried out and many methods considered and attempted – shown a minimum reached. Activation energies calculated for 0K and 298K and compared to literature - v.good. No need for graph (2) as doesn’t really show additional information – only 2 points on line. Understanding: Outstanding introduction, and v. good understanding of the steps taken. E.g. A good understanding of the benefits of carrying out a rough optimisation before carrying out higher-level optimisation. Good understanding to why such methods were applied, the pros and cons, and the use of keywords in the input. Gauche/anti conformers and their energies analysed thoroughly. A great deal of individual thought given! Diels alder: Presentation: Excellent, as above. Excellent use of animations and figures to display results. Results: Generally very good. MOs for reactants and TS correct, and a very good understanding of their interaction. Very thorough investigation into TS, investigating a number of methods and even considering IRC analysis. Exo/Endo: correct alignments and MOs for these. Structural analysis given in great detail. Endo correctly noted as lowest in energy and good explanation given. A better angle of the MO figures may make the secondary orbital overlap apparent, as is hard to see. Understanding: Very good. A thorough explanation to the steps given throughout. Good understanding of HOMO/LUMO interactions and a very nice explanation of allowed and forbidden reactions. All results explained scientifically, in very good detail. Well done! You have an outstanding understanding of the topic and your work was a pleasure to read. Do consider a computational research project in the future.