Talk:Mod:ll4012

Introduction Short general introduction. Be careful: Gaussview is a software that allows you to visualize the molecules, the molecular orbitals for example and to interact with Gaussian – Gaussian actually does the calculation not Gaussview.

Cope rearrangement Some conformers were successfully identified - although not all of them - with a short comment about their relative energy. How did you check that the stationary points you found were minima on the potential energy surface? Chair and Boat structures successfully identified with the different methods proposed. Good interpretation of the IRC calculation. What do you conclude about the preferred mechanism?

Diels-Alder “In order for a HOMO-LUMO interaction to be allowed, the two orbitals must have different symmetries to the plane of symmetry in the TS. For example, the LUMO of ethene is antisymmetric, whereas the HOMO of cyclohexadiene is symmetric to the plane. This means the HOMO-LUMO interaction is allowed.” The fragment orbitals are the important criteria. In order for the reaction to be allowed the HOMO and LUMO of the fragments must be of the same symmetry (<http://en.wikipedia.org/wiki/Frontier_Molecular_Orbital_Theory>) “As the Van der Waals radius of carbon is 1.7 Å[4], we would expect a C-C bond to be around 3.4 Å” The van der Waals radius indicates (in a qualitative way) about the distance at which the two molecules would begin to interact. The sp3-sp3 C-C bond length is much less than two times this distance (~150 pm). The lowest real frequency indicates that symmetry breaking is uphill in energy and that symmetry is therefore preserved through the TS.