Effect of Substituting Oxygen for Terminal Nitrogen in Aniline Oligomers: a DFT Comparison of Hydroxyl and Amino Terminated Aniline Trimers

Abstract

Quantum mechanical density functional theory (DFT) calculations are reported for N,N'-bis(4'-hydroxyphenyl)-1,4-quinonediimine [henceforth referred to as the hydroxyl terminated trimer], a derivative of previously investigated aniline trimers. Calculations are also reported on all isomers, common oxidations states, and hydrochloride salts of this material. The significance of replacing terminal amino groups by hydroxyl groups is detailed. The hydroxyl terminated trimer has a calculated electron affinity larger than that of the corresponding amino terminated aniline trimer N,N'-bis(4'-aminophenyl)-1,4-quinonediimine. The electron affinity of the anti conformer of the hydroxyl terminated emeraldine base trimer is 0.059767 hartrees (37.5 kcal mol(-1)), whereas that of the amino terminated form is 0.052728 (33.1 kcal mol(-1)). The electron affinity of the anti conformer of the hydroxyl terminated emeraldine dihydrochloride salt trimer is 0.130546 hartrees (81.9 kcal mol(-1)), whereas that of the amino terminated dihydrochloride salt is only 0.118972 (74.7 kcal mol(-1)). Because previous work has suggested that a larger electron affinity in the salt form leads to improved effectiveness in the role of corrosion inhibitor, these high-level calculations suggest a new and superior material for this application.