Hydrogen bonding between acetone and silica gel, as studied by NMR

C-13 NMR spectra and relaxation parameters (T-1(H), T-1(C), T-1 rho(H), T-C H) were measured via CP-MAS and DP-MAS techniques as a function of acetone loading level in acetone/SiO2 samples at 25 degrees C. T-1(H) and T-1 rho(H ) values were also measured via Si-29 CP-MAS experiments. Peak positions an d relaxation parameters are averaged by rapid exchange between different ac etone interaction sites on the surface. The data were analyzed in terms of a surface equilibrium of adsorbed acetone units between hydrogen-bonding an d non-hydrogen-bonding sites. Data analysis by this model yielded the surfa ce concentration of hydrogen-bonding (silanol) sites (1.5 nm(-2)) and the e quilibrium constant (K = 3.0 nm(2)). Variable-temperature experiments (124- 297 K) at three loading levels yielded values of Delta H degrees (-5.8 +/- 0.3 kJ mol(-1)) and Delta H degrees (-12.5 +/- 0.7 J K-1 mol(-1)). A self-c onsistent, qualitative interpretation of measured relaxation parameters is made in terms of the relative mobilities of hydrogen-bonded (less mobile) a nd non-hydrogen-bonded (more mobile) acetone on the SiO2 surface.