✍ Scribed by Volker Rüdiger; Hans-Jörg Schneider; Vitally P. Solov'ev; Vladimir P. Kazachenko; Oleg A. Raevsky
No coin nor oath required. For personal study only.
Thermodynamics of 18-crown-6 complexes with ammonium energetically equally good conformations of an essentially undistorted D 3d crown accepting either 3 linear hydrogen cations (NH 4 , MeNH 3 , Me 2 NH 2 , Me 3 NH, Me 4 N, Et 4 N, PhNH 3 , and PhCH 2 NH 3 ) in methanol were determined by bonds, or 6 bifurcated bonds from the primary ammonium cations. Complexation equilibria were measured with titration calorimetry. The results show strong contributions from entropy terms counteracting the enthalpy of PhNH 3 , and PhCH 2 NH 3 in water, 2-propanol, tert-butyl alcohol, n-octanol, DMF, DMSO, pyridine, HMPT and complexation, and a linear decrease of the complexation free energy ∆G with the number of available N-H hydrogen acetone mostly by calorimetry, in some cases by potentiometry. The observed association constants varied by bonds. In several cases formation of relatively strong complexes containing two ammonium ions per crown unit factors of up to 1000; the solvent effects can be described generally as a linear function of the hydrogen bond was observed. Tetramethylammonium ions show no detectable association with the crown ether, demonstrating accepting power of the solvent molecules, in line with the mechanisms derived above. The lgK and ∆H values of the the absence of significant Coulomb-type interaction between the partial charges at the crown ether oxygen and the N + -C-complexation of the PhNH 3 or PHCH 2 NH 3 cation with 18crown-6 ligand are compared with a large range of available H atoms. Ammonium ions bind to aza crown ethers with almost equal affinity as to the all-oxygen anologs only, if solvent properties. The best correlations (R ഠ 0.9) for lgK (or ∆G) are obtained with values characterizing the electron methyl groups at the nitrogen atoms force the lone pairs into equatorial position. Molecular mechanics calculations donor capacity of the solvent (C a , β*, DN) for lgK, as found earlier for complexes between K + and 18C6. (CHARMm) of corresponding gas-phase complexes yield geometries and energies in agreement with this, with mited range of solvents (nitrobenzene, acetonitrile, N,N-di-
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Supramolecular Chemistry. Part 60. Solvent Effects on Crown Ether Complexations. -The complexation between potassium salts and 18-crown-6 in 14 different solvents is studied. The stability constant K increases by ¿ 104 from water to pure methanol or to propylene carbonate. Linear correlations are ob
AbstractÐAmmonium nitrate coordinates to 18-crown-6 through a near-ideal `tripod' arrangement of hydrogen bonds to alternate crown ether oxygen atoms. Ion pairing interactions are apparent, with the strength of this ion pairing interaction appearing to be reduced by hydration, representing a potenti