Hydrogen bond-aromaticity cooperativity in self-assembling 4-pyridone chains

• Published in: Journal of computational chemistry 2016-01, Vol.37 (1), p.59-63
• Main Authors: Anand, Megha, Fernández, Israel, Schaefer III, Henry F., Wu, Judy I-Chia
• Format: Article
• Language: English
• Subjects: Aromaticity; Assembling; Chains; Chemical bonds; Chemical engineering; Chemistry; Coupling; Decomposition; Electrons; energy decomposition analysis; hydrogen bonding; Hydrogen bonds; Hydrogen storage; Nuclei; nucleus independent chemical shifts; Polarization; self-assembly; Series (mathematics)
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.23976

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 π‐electron delocalization in the six‐membered ring. The resulting H‐bonded 4‐pyridone units display enhanced π‐aromatic character (both magnetically and energetically) and their corresponding NH···OC interactions are strengthened. These π‐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. © 2015 Wiley Periodicals, Inc. Hydrogen bonding interactions can polarize the π‐systems of 4‐pyridones to increase cyclic (4n+2) π‐electron delocalization. The resulting H‐bonded six‐membered rings exhibit enhanced π‐aromaticity and the corresponding NH···OC interactions are strengthened. Extended H‐bonded 4‐pyridone chains exhibit high degrees of such cooperativity, even when each of the neighboring 4‐pyridone rings are twisted to preclude direct π‐overlap between the H‐bonded units.