O-H/N-H bond dissociation energies in 1,4-hydroquinone, 4-hydroxydiphenylamine, N,N′-diphenyl-1,4-phenylenediamine, and their phenoxyl and aminyl radicals

Abstract

Gas phase bond dissociation energies (BDE) O-H/N-H in hydroquinone (H₂Q), 4-aminophenol (AP), 1,4-phenylenediamine (PDA), 4-hydroxydiphenylamine (HDPA), N,N′-diphenyl-1,4-phenylenediamine (DPPDA) as well as in their phenoxyl/aminyl radicals have been determined using a combined technique of quantum chemical calculation. The technique included a series of DFT (PBE1PBE, TPSSTPSS, M06-2X), ab initio (DLPNO-CCSD(T)) methods with valence 3ξ-basis sets, composite methods of Gaussian family (G4) and Weizmann theory with ab initio Brueckner Doubles (W1BD), as well as reference reactions of different levels of structural similarity. W1BD method was used in combination with isodesmic reactions for BDE estimation (kJ∙mol⁻¹) of compounds with the only aromatic fragment: BDE_O-H = 352.3 (H₂Q), 340.0 (AP), BDE_N-H = 371.2 (AP), 364.1 (PDA) – in molecules; and BDE_O-H = 230.4 (H₂Q), 228.8 (AP), BDE_N-H = 260.0 (AP), 257.1 (PDA) – in corresponding radicals. These values were further applied to estimate the BDEs in HDPA and DPPDA within the homodesmotic reference process and less resource-intensive ab initio methods: BDE_O-H = 341.4 (HDPA), BDE_N-H = 352.9 (HDPA), 351.3 (DPPDA) for molecules; BDE_O-H = 237.4 (HDPA), BDE_N-H = 247.4 (HDPA), 252.6 (DPPDA) for radicals. DFT methods give similar results but a slightly larger standard error of calculation. The found values of BDE(O-H/N-H) are compared with literature data; the effect of solvation on BDEs is discussed.