Phenyl-substituted 1-arylazo-2-naphthols (AAN) display ...HN-N=C-C=O... <-/-> ...N=N-C=C-OH... ketohydrazone-azoenol tautomerism and can form intramolecular resonance-assisted H-bonds from pure N-H...O to pure N...H-O through tautomeric and dynamically disordered N-H...O <-/-> N...H-O bonds according to the electronic properties of their substituents. Three compounds of this series (m-OCH3-AAN = mOM; p-Cl-AAN = pCl; and p-NMe2-AAN = pNM2) have been studied by X-ray crystallography at four temperatures (100-295 K), showing that the remarkably short H-bonds formed (2.53 <= d(N...O) <= 2.55 Angstrom) are a pure N-H...O in mOM, a dynamically disordered mixture in pCl (N-H...O : N...H-O = 69:31 at 100 K), and a statically disordered mixture in pNM2 (N-H...O : N...H-O = 21:79 at 100 K). These compounds, integrated by the p-H-, p-NO2-, p-F-, and p-O--substituted derivatives, have been emulated by DFT methods (B3LYP/6-31+G(d,p) level) with full geometry optimization of the stationary points along the proton-transfer (PT) pathway: N-H...O and N...H-O ground states and N...H...O transition state. Analysis of DFT-calculated energies and geometries by the methods of the rate-equilibrium Marcus theory shows that all H-bond features (stability and tautomerism, as well as position and height of the PT barrier) can be coherently interpreted in the frame of the transition-state (or activated complex) theory by considering the bond as a chemical reaction N-H...O <-/-> N...H...O <-/-> N...H-O which is bimolecular in both directions and proceeds via the N...H...O PT transition state (the activated complex).
Variable-temperature X-ray crystallographic and DFT computational study of the N-H...O/N...H-O tautomeric competition in 1-(arylazo)-2-naphthols. Outline of a transiton-state hydrogen-bond theory
GILLI, Paola;BERTOLASI, Valerio;PRETTO, Loretta;GILLI, Gastone
2005
Abstract
Phenyl-substituted 1-arylazo-2-naphthols (AAN) display ...HN-N=C-C=O... <-/-> ...N=N-C=C-OH... ketohydrazone-azoenol tautomerism and can form intramolecular resonance-assisted H-bonds from pure N-H...O to pure N...H-O through tautomeric and dynamically disordered N-H...O <-/-> N...H-O bonds according to the electronic properties of their substituents. Three compounds of this series (m-OCH3-AAN = mOM; p-Cl-AAN = pCl; and p-NMe2-AAN = pNM2) have been studied by X-ray crystallography at four temperatures (100-295 K), showing that the remarkably short H-bonds formed (2.53 <= d(N...O) <= 2.55 Angstrom) are a pure N-H...O in mOM, a dynamically disordered mixture in pCl (N-H...O : N...H-O = 69:31 at 100 K), and a statically disordered mixture in pNM2 (N-H...O : N...H-O = 21:79 at 100 K). These compounds, integrated by the p-H-, p-NO2-, p-F-, and p-O--substituted derivatives, have been emulated by DFT methods (B3LYP/6-31+G(d,p) level) with full geometry optimization of the stationary points along the proton-transfer (PT) pathway: N-H...O and N...H-O ground states and N...H...O transition state. Analysis of DFT-calculated energies and geometries by the methods of the rate-equilibrium Marcus theory shows that all H-bond features (stability and tautomerism, as well as position and height of the PT barrier) can be coherently interpreted in the frame of the transition-state (or activated complex) theory by considering the bond as a chemical reaction N-H...O <-/-> N...H...O <-/-> N...H-O which is bimolecular in both directions and proceeds via the N...H...O PT transition state (the activated complex).I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
