Abstract: Energies of cation-dipole interactions in ML and/or ML2(M=Li, Na, K; L=12-crown-4, 15-crown-5, 18-crown-6 or 24-crown-8) are calculated based on the molecular geometry of these complexes. The effect of M/L ratio and geometric configuration on the stability of these complexes is considered to determine their relative stability in the absence of solvents. The stability order thus established is confirmed by radiotracer method using 125I and 82Br. Thus we can predict how metal ions affect the nucleophilic labelling reaction in a crown ether medium.