Tuning the strength of the resonance-assisted hydrogen bond in acenes and phenacenes with two o-hydroxyaldehyde groups - The importance of topology

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Pareras, Gerard
Szczepanik, Dariusz Wojciech
Duran, Miquel
Solà, Miquel
Simon, Silvia
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The fact that intramolecular resonance-assisted hydrogen bonds (RAHBs) are stronger than conventional ones is attributed to the partial delocalization of the π-electrons within the hydrogen bond (HB) motif, the so-called quasi-ring. If an aromatic ring is involved in the formation of the RAHB, previous studies have shown that there is an interplay between aromaticity and HB strength. Moreover, in 1,3-dihydroxyaryl-2-aldehydes, some of us found that the position of the quasi-ring formed by the substituents interacting through RAHB influences the strength of the H bonding, the HBs being stronger when a kinked-like structure is generated by formation of the quasi-ring. In this work, we explore this concept further by considering a set of acenes and phenacenes of different sizes with two o-hydroxyaldehyde substituents. Calculations with the CAM-B3LYP/6-311++G(d,p) + GD3B method show that for long acenes or phenacenes, once the substituent effect loses importance because quasi-rings are pulled apart far from each other, the different topologies rule the HB distances. This fact can be explained in most cases using an extended Clar’s aromatic π-sextet model. In some kinked systems, however, the justification from the Clar model has to be complemented by taking into account the repulsion between hydrogen atoms. Triphenylene-like compounds with different numbers of benzene rings have been studied, finding out a very good relationship between aromaticity of the ipso- and quasi-rings with the RAHB distances. This result confirms the importance of the communication of the π-systems of the ipso- and quasi-rings.
Hydrogen bond , Resonance-assisted hydrogen bonds , RAHB , Aromaticity
Pareras, G., Szczepanik, D. W., Duran, M., Solà, M. and Simon, S. (2019) 'Tuning the strength of the resonance-assisted hydrogen bond in acenes and phenacenes with two o-hydroxyaldehyde groups - The importance of topology', Journal of Organic Chemistry, 84(23), pp. 15538-15548. doi: 10.1021/acs.joc.9b02526
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© 2019, American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Organic Chemistry, copyright © American Chemical Society, after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/acs.joc.9b02526