Collision Frequency in Solution; Kinetics of Diene Syntheses in Solution and in the Gaseous State

IN the Arrhenius equation , C is the collision frequency and P the steric factor. For gas reactions the kinetic theory gives C 1011. Bimolecular reactions in solution can be divided into two main types1: (a) reactions involving simple ions where Z 1011; (b) reactions involving molecules with many internal degrees of freedom, where Z 1011 (slow reactions). For reactions (a) a statistical mechanical treatment shows2 that P should be of order unity and here it can be concluded that C is of order 1011. For reactions (b) a statistical mechanical calculation of P is difficult and thus it is possible a priori that C falls below the gas value by several powers of ten.