Quantitative study of interactions between oxygen lone pair and aromatic rings: substituent effect and the importance of closeness of contact. Academic Article uri icon


  • Current models describe aromatic rings as polar groups based on the fact that benzene and hexafluorobenzene are known to have large and permanent quadrupole moments. This report describes a quantitative study of the interactions between oxygen lone pair and aromatic rings. We found that even electron-rich aromatic rings and oxygen lone pairs exhibit attractive interactions. Free energies of interactions are determined using the triptycene scaffold and the equilibrium constants were determined by low-temperature 1H NMR spectroscopy. An X-ray structure analysis for one of the model compounds confirms the close proximity between the oxygen and the center of the aromatic ring. Theoretical calculations at the MP2/aug-cc-pVTZ level corroborate the experimental results. The origin of attractive interactions was explored by using aromatic rings with a wide range of substituents. The interactions between an oxygen lone pair and an aromatic ring are attractive at van der Waals' distance even with electron-donating substituents. Electron-withdrawing groups increase the strength of the attractive interactions. The results from this study can be only partly rationalized by using the current models of aromatic system. Electrostatic-based models are consistent with the fact that stronger electron-withdrawing groups lead to stronger attractions, but fail to predict or rationalize the fact that weak attractions even exist between electron-rich arenes and oxygen lone pairs. The conclusion from this study is that aromatic rings cannot be treated as a simple quadrupolar functional group at van der Waals' distance. Dispersion forces and local dipole should also be considered.

published proceedings

  • J Org Chem

author list (cited authors)

  • Gung, B. W., Zou, Y., Xu, Z., Amicangelo, J. C., Irwin, D. G., Ma, S., & Zhou, H.

citation count

  • 102

complete list of authors

  • Gung, Benjamin W||Zou, Yan||Xu, Zhigang||Amicangelo, Jay C||Irwin, Daniel G||Ma, Shengqian||Zhou, Hong-Cai

publication date

  • January 2008