NMR and viscosity B coefficients for spherical nonelectrolytes in nonaqueous solvents

The NMR and viscosity B coefficients for tetraalkylsilanes (R4Si, R=Me and Et) and tetraalkyltins (R4Sn, R=Pr, Bu, and Pen) were measured in benzene, cyclohexane, and chloroform at various temperatures under atmospheric pressure. Both of the B coefficients for the small solutes, Me4Si and Et4Si, were negative and slightly increased with increasing temperature. Those for the larger solutes, Pr4Sn, Bu4Sn, and Pen4Sn, were positive and slightly decreased with increasing temperature. The solute size and temperature dependences of the B coefficients indicate that the attractive dispersion interaction between solute and solvent is important in determining the local rotational dynamics of solvent molecules in the vicinity of a nonelectrolyte solute. The local effect on the rotation of solvent molecules in nonaqueous nonelectrolyte solutions is much smaller than that in aqueous solutions.