Proton or Hydrogen Transfer? Charge Distribution Analysis

摘要

The meaning of terms"proton transfer"(PT)and"hydrogen transfer"(HT),commonly encountered in the literature,is not always unambiguous,especially in the case of intramolecular tautomerization processes.Depending on the used criterion,the same reaction may be classified as either PT or HT.Two criteria for distinguishing between PT and HT are discussed:(a)formal translocation of charge;(b)the reaction mechanism,in particular the coupling between the motion of the proton and the electron density redistribution.The analysis is illustrated using the values of ground and excited state partial charges calculated for three well-known examples of molecules that undergo photo-induced and/or ground state tautomerization:2-hydroxyacetophenone,2,2'-bipyridyl-3,3'-diol,and porphycene.