Abstract: Thecoordination reaction of alkali metal ions with methyl Benzo-18-Crown-6 derivates containing 1-3 methyl groups on their crown ring was studied by ¹³CNMR method, which gives the information about the conformation of the complexes in solution.The electric charge density of carbon atoms on the crown ring was calculated by CNDO/2 method and a linear relationship between electric charge density and corresponding chemical shift was found.The stability constants of Na⁺-crown complexes were determined by ²³NaNMR,showing also a linear relationship with the number of methyl groups on the crown ring. lgβ= 4.16-0.20n wherein n denotes the number of methyl groups.