Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

13C NMR spectra and relaxation parameters (T1H, T1C, T1ρH, TCH) were measured via CP-MAS and DP-MAS techniques as a function of acetone loading level in acetone/SiO2 samples at 25 °C. T1H and T1ρH values were also measured via 29Si CP-MAS experiments. Peak positions and relaxation parameters are averaged by rapid exchange between different acetone interaction sites on the surface. The data were analyzed in terms of a surface equilibrium of adsorbed acetone units between hydrogen-bonding and non-hydrogen-bonding sites. Data analysis by this model yielded the surface concentration of hydrogen-bonding (silanol) sites (1.5 nm-2) and the equilibrium constant (K = 3.0 nm2). Variable-temperature experiments (124−297 K) at three loading levels yielded values of ΔH° (−5.8 ± 0.3 kJ mol-1) and ΔS° (−12.5 ± 0.7 J K-1 mol-1). A self-consistent, qualitative interpretation of measured relaxation parameters is made in terms of the relative mobilities of hydrogen-bonded (less mobile) and non-hydrogen-bonded (more mobile) ...