Question

If I have conjugated molecule containe Maine chain liknked to donors groups on both end and they are symmetry .. my question is :

when I would to explain the molecular orbitals shape what the terms should I used if the HOMO and LUMO were separated on the double bonds of the main chains to some pi bonds of the donors groups at the both sides!

I mean what this part of the whole molecule called ? Phase ? Or inter ? Or what ??

Answer 1

When a conjugated molecule, let's say a diene, with the same pi-bonding groups on its both ends, has to be explained in terms of the HOMO and LUMO which were separated on the double bonds of the main chain, the explanation can be given as shown below.

For e.g., in a Diels-Alder reaction, HOMO of the diene reacts with LUMO of dienophile to form the cycloadduct. The stereochemistry of the adduct depends on the conditions of light or heat.

If the reaction is under light radiation, then (4n+2) - h - CON rotation (same side rotation), i.e. the end groups on the diene will be in the same phase in the cycloadduct (similar to that of diene).

If the reaction is occurring in thermal condition, then (4n+2) - - DIS rotation (opposite side rotation), i.e. the end groups on the diene will be in the opposite phase in the cycloadduct (opposite to that of diene).