The Libido Rule

General-acid or general-base catalysis will occur when a fherinodynainically unfavorable proton transfer in the ground state is converted to a thermodynamically favorable transfer in the transition state. 

if the substrate becomes more basic along the reaction coordinate of the rate-determining step and ultimately leads to a thermodynamically favorable proton transfer from a coordinated acid, general catalysis will occur. The proton transfer is thermodynamically viable only during the rate-determining step. This means that the pKa of a general-acid catalyst must be between the pK values of a fully protonated reactant and the protonated product, with the assumption that the pKa of the transition state and product are similar (Eq. 9.45). A similar statement can be made for a general-base-catalyzed reaction. 

---

Use the libido rule to predict which of the following acids could give specific catalysis or general catalysis in the following reaction (the pX., of the conjugate acid of an imine is around 4 to 5) HCl, picric acid, acetic acid, ammonium, and phenol. 

---