Hydrogen Bond-Aromaticity Cooperativity in Self-Assembling 4-Pyridone Chains

Self-assembling building blocks like the 4-pyridone can exhibit extraordinary H-bond-aromaticity coupling effects. Computed dissected nucleus independent chemical shifts (NICS(1)(zz)), natural bond orbital (NBO) charges, and energy decomposition analyses (EDA) for a series of hydrogen (H-) bonded 4-pyridone chains (4-py)(n) (n = 2 to 8) reveal that H-bonding interactions can polarize the 4-pyridone exocyclic C=O bonds and increase 4n+2 pi-electron delocalization in the six-membered ring. The resulting H-bonded 4-pyridone units display enhanced pi-aromatic character (both magnetically and energetically) and their corresponding N-H center dot center dot center dot O=C interactions are strengthened. These p-electron polarization effects do not depend on the relative orientations (co-planar or perpendicular) of the neighboring 4-pyridone units, but increase with the number of H-bonded units. (C) 2015 Wiley Periodicals, Inc.