Significance of electron excitation in chemical reactions

Abstract

Reactions of thermal electron and photoelectron transfer between aromatic amines and anhydrides in acetonitrile and dimethyl-formamide have been investigated. The activation energy Ea of the TMPD reaction and the frequency of the charge-transfer band decrease with inceasing electron affinity of the acceptor. Using the TMPD–DBPM system as an example it is found that the energy values of the luminescent level estimated from the energy of the charge-transfer band (96.3 kJ mol–1) and the sum of the activation energy and the enthalpy of complexation in toluene coincide. The results suggest that thermal electron transfer proceeds through the electronically excited state of the charge-transfer complex. The addition of an acid accelerates both thermal and photo-initiated electron transfer. A mechanism is proposed in which electron transfer proceeds via the electronically excited state of a complex containing a hydrogen bond involving the participation of a mobile hydrogen atom. A comparison between the reactions of primary and methyl-substituted amines is made.