Aromatic nucleophilic substitution in aprotic solvents using hydrogen-bonded biological amines; kinetics studies and quantum chemical calculations

Abstract

Intermolecular and intramolecular non-bonding interactions play a crucial role in determining physical and biological properties of relevant amines, and we have recently reported that they are also responsible for changing mechanisms in aromatic nucleophilic substitution (ANS) involving amine nucleophiles, when they are carried out in solvents of low permittivity. The present work describes ANS in toluene with a series of biological amines that can set specific hydrogen bonding (H bonding) interactions due to their special molecular structures. Kinetic studies of ANS with 2-amino-5-guanidinopentanoic acid (arginine), (4-aminobutyl)guanidine (agmatine), 2,6-diaminohexanoic acid (lysine) and 3,4-dihydroxyphenethylamine (dopamine) towards 1-chloro-2,4-dinitrobenzene in toluene are reported. The kinetic results are compared with those obtained with 2-guanidinobenzimidazole and 2-(1H-imidazole-4-yl) ethanamine (histamine); both amines form intramolecular H bonds. The special types of H bonding were also investigated by ab initio density functional theory calculations, at the B3LYP/6-31++G(d,p) level, including counterpoise corrections to account for basis set superposition errors and solvent effects at the polarized continuum model level.