Water Entrapped inside Fullerene Cages: A Potential Probe for Evaluation of Bond Polarization

The concept of the bond polarization is a useful tool to understand chemical reactions and fundamental properties of compounds. However, experimental considerations are limited owing to its difficulty of reliable description. We demonstrated that geometrically isolated H₂ O inside the cage of fullerene C₆₀ is a possible probe to evaluate the polarization degree of covalent bonds C(C₆₀ )-X (X=heteroatom) on the C₆₀ cage. The ¹ H NMR relaxation times of entrapped H₂ O have been systematically measured at variable temperatures for H₂ O@C₆₀ X (X=CR₂ , NR, O, and O₂ ). The results followed in the order of electronegativities of C (2.55), N (3.04), and O (3.44), indicating that entrapped H₂ O can sensitively respond to the degree of the bond polarization.