頁籤選單縮合
題 名 | Thermodynamics of Complexation Reactions of Lithium Ion with Dibenzo-14-Crown-4 and Its Analogs in Nonaqueous Solvents |
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作 者 | 陳吉松; 蔡瑞燦; 王時俊; 鍾崇燊; | 書刊名 | Journal of the Chinese Chemical Society |
卷 期 | 40:3 1993.06[民82.06] |
頁 次 | 頁255-261 |
分類號 | 340 |
關鍵詞 | Thermodynamics; Lithium complexes of DB14C4 analogues; |
語 文 | 英文(English) |
英文摘要 | Formation constants of Li�呃omplexes with 4-substituted dibenzo-14- crown-4 (DB14C4;4-substituted group: methyl-, tert-butyl-, H-, bromo-, chloro-, formyl-, nitro-) ligands were determined by �� Li NMR spectrometry for solutions in nitromethane (NM), acetonitrile (ACN), propylene carbonate (PC), acetone (AC), Pyridine (Py), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and N,N'-dimethyl formamide (DMF). Only a 1:1 complex was formed in solvents with a small or medium donor number. The formation constants of these complexes are strongly influenced by the size of the metalion-the effect of the size of the cavity, by the solvent and by substituent. The stability of lithium ion with different substituents on DB14C4 decreases in the order methyl- > tert-butyl- > H- > bromo- > chloro- > formyl- > nitro-in various solvents. A good Hammett correlation was found by plotting log K �� vs. Σσ in PC and AC. The extent of the substituent effect increases as the donor number of solvent decreases. The complexes were both enthalpy and entropy stabilized. The same magnitude of �� S ° value for different substituents indicates formation with a similar configuration upon complexation between crown ether and lithium ion. A slight variation in entropy contribution was observable depending on the nature of the alkyl substituent, whereas a large variation in enthalpic contribution shows a remarkable substituent effect upon complexation; the effect can reach 70% in magnitude. |
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