H₂O/Olefinic-π Interaction inside a Carbon Nanocage

Abstract

The H₂O/CH₂═CH₂-type hydrogen-bonding (H-bonding) model was experimentally constructed using a water complex of an open-cage C₆₀ derivative, in which an olefinic double bond and a single molecule of H₂O are geometrically confined. To investigate OH/π-type H-bonding, that is, H₂O···(C═C) interaction, we performed ¹H NMR spectroscopic studies that demonstrated the monotonic downfield shift of the proton signal corresponding to H₂O with remarkable rotational perturbation by lowering the temperature. From the temperature dependence of the angular momentum correlation time (τ_J), the interaction energy was quantitatively estimated to be ca. 0.3 kcal/mol. The computational studies were thoroughly conducted to clarify its inherent nature. As a consequence, the orientation of H₂O was found to play a prominent role in varying the bonding strength as well as contribution from the electrostatic attraction and orbital-orbital interaction significantly driven by the favorable orbital overlap identified as π(C═C) → σ*(OH) interaction.