Electronic absorption spectra studies on donor acceptor interactions weak and strong

Abstract

The possible role of Electron Donor Acceptor complexes or interactions in controlling and modifying the electron or charge flow, as a bridge between molecular components in biological systems is a fascinating area of research. In almost all such studies with quinones as acceptors the model compound has been Chloranil, which is tetrachloro-1,4 benzoquinone. This is too strong an acceptor and insoluble in water. But systems in vivo are often reversible and involve aqueous and ionising media. newline newlineIn the first part of the investigation 2,5 dichloro, 3-6-dimethoxy p-benzoquinone CMBQ is the quinone chosen. For study with its accepting capacity moderated by two, methoxy groups in place of chlorines. It is soluble in water. Its complexing ability has been studied first in carbon tetrachloride with the aromatic hydrocarbons hexamethylbenzene, fluorene, naphthalene, durene and acenapthene. The interaction is found to be very weak even with the fairly strong donor HMB. With all the other donors contact pair interaction seems to prevail and intensity borrowing from the donor excited state appears to contribute to the increased absorption in the spectra. Even carbontetrachloride is shown to compete with this quinine as an acceptor and this has been dramatically demonstrated in the specific solvent effect that has, brought forth some special features in the results. newline newlineIn spite of this moderation in its electron accepting ability this quinone is found to have strong interaction with aliphatic amines which act as n-donors. This aspect forms the subject of study itr the second part of this dissertation. N-butylamine and other amines aire found to, interact with CMBQ in water solution giving rise to changes in .the absorption spectra with time. Beyond the stage of outer complex formation, an ionic complex leads on further to a nucleophilic substitution reaction showing up a 3,6-diamino substituted product. The kinetics has been investigated.