SAR of Cholinocepter agonists Acyloxy group Quaternary ammonium H3CO-CH2-CH2+-N(CH3)Cl Ethylene group Ing's rule of five This rule suggests that there should be no more than five atom between the nitrogen and the terminal hydrogen atom for maximal muscarinic potency.SAR of Cholinocepter agonists Ing’s rule of five: This rule suggests that there should be no more than five atom between the nitrogen and the terminal hydrogen atom for maximal muscarinic potency