Limiting mutual diffusion coefficients of aromatic compounds in acetone have been measured at 298.2 K by using the chromatographic peak-broadening method. The data of the polar and nonpolar pseudoplanar solutes are compared, and the effects of molecular association on diffusion as well as the solvation numbers are determined. It is found that the effects of hydrogen bonding are such that -OH>-NH2>-SH, and that the solvation numbers are approximately equal for solutes containing the same polar group. Using ab initio molecular orbital theory, molecular solute-acetone interaction energies have been calculated. There exists a nearly linear relationship between the interaction energy and the effect of solute-solvent association on diffusion. The applicability of the rough-hard-sphere theory to the diffusion of associated molecules is discussed.