The transmission of electronic substituent effects along the polyene chain: evaluation of through-bond and through-space contributions

Transmission between various parts of molecules determines their reactivity and is important from the perspective of molecular recognition. In a recent paper, the correlation between substituent electronic properties and those of the rest of molecules has been studied using long substituted polyphenylene hydrocarbons. The distance attained between interacting sites (between a substituent and an extreme carbon atom) was 119 Å. The present study was planned to investigate whether similar interactions can be found when the transmitting medium is not a polyphenylene unit, but a polyene one. Some questions had to be answered: How rapidly do interactions between a substituent at one end of a molecule and phenyl ring at the other end decline with the increasing distance between two sites? How would this interaction change upon the removal of some polyene units from inside the molecule and what contribution would the units have to the through-space interactions? What measure characterizes the electronic properties of a substituent attached to the end of a polyenic chain? It was found that the through-space interaction contributions increased as molecules lengthened, but even for the longest molecules, the through-bond mechanism was responsible for about one half of the overall transmission whereas the through-bond transmission dominated for shorter molecules.