Reference of 14187-32-7. Chemistry is an experimental science, and the best way to enjoy it and learn about it is performing experiments.Introducing a new discovery about 14187-32-7, Name is Dibenzo-18-crown-6
Mechanism of Complexation of Crown Ethers as a Function of Alkali Ions and the Rigidity of the Ligands
The kinetics of complexation of Na+ and K+ with the crown ethers dicyclohexano-18-crown-6 (DH18C6) and dibenzo-18-crown-6 (DB18C6) in the solvent dimethylformamide (DMF) and Na+ with DH18C6 in methanol (MeOH) have been studied by ultrasonic relaxation techniques in the frequency range from <*>1 to <*>400 MHz.The results are compared with data for the same cations reacting with 18-crown-6 (18C6).In DMF at 40 deg C for Na+ added to DH18C6 in molar ratio R <*> 1 two relaxation processes apper that are displaced within a factor of two in relaxation frequencies from those of the system Na+ = 18C6.For K+ added to DH18C6 (R=1) two relaxation processes appear at about the same frequency as for the system K+ + 18C6.The difference between the results for Na+ and K+ may reflect the closer fit of the potassium cation radius with the macrocycle cavyty.For Na+ + DB18C6 in DMF at 40 deg C two relaxation processes, the first at about the same frequency as for DH18C6 but the second below 1 MHz, are detectable.For K+ + DB18C6 in DMF at 40 deg C, both relaxation frequencies are dramatically shifted with the lower one lying below 1 MHz.The behavior of the process at lower frequency is compatible with the progressive increase of ligand ring rigidity in going from 18C6 to DH18C6 and to DB18C6, if the rate-determining factor of the process at the lower frequency is attributed to the encirclement of the metal cation by the ligand.In MeOH the surmise that the ligand rearrangement also plays a role in the reaction coordinate energy profile of the complexation of alkali metal cations added to 18C6 is supported by new data now available with the resonator technique, the data revealing two relaxation processes for both Li+ and Na+.In MeOH, the system Na+ + DH18C6 gives rise to two detectable relaxation processes at 25 deg C.Surprisingly, they are a factor of two faster than for the system Na+ + 18C6 (at variance with the same system in DMF solvent).For Li+ + DH18C6 in MeOH from the only run available it appears that the process at high frequency is somewhat faster than for Li+ + 18C6 in MeOH whereas the one at low frequency is lower by a factor of 3 or more with respect to the one in the system Li+ + 18C6.This complex behavior may indicate a concerted process in which both the solvent substitution and ligand rearrangement influence the energy profile of the overall process.In the majority of cases the activation parameters have been evaluated from the temperature dependence of the relaxation processes.
If you are hungry for even more, make sure to check my other article about 14187-32-7. Reference of 14187-32-7
Reference£º
Chiral Catalysts,
Chiral catalysts – SlideShare