The complerties properties of ohelating agents are largely inflnenoed by the intramoleoular hydrogen bonding, which can be predicated experimentallyby phyeico-chemical method.This paper describes a study of the relationship between.the chemical structure and the strength of intramoleoular hydrdgen bonding of ohelating agents by PMO method.It is found that the PMO method can be applied snooasafully in such ohelating agents which may be regarded as ieooonjngated.system of alternant hydrocarbon (AH), especially for odd AH.