Термодинамика образования водородных связей N-метилимидазола и N-метилпиррола с алифатическими спиртами
| Autor: | Cоломонов, Борис |
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| Jazyk: | ruština |
| Rok vydání: | 2009 |
| Předmět: | |
| Zdroj: | Ученые записки Казанского университета. Серия Естественные науки. |
| ISSN: | 2542-064X |
| Popis: | Изучены процессы водородного связывания N-метилимидазола, N-метилпиррола и пиридина с хлороформом и алифатическими спиртами. Показано, что протоноакцепторность этих соединений увеличивается в ряду N-метилпиррол-пиридин-N-метилимидазол. Обнаружено, что энтальпия специфического взаимодействия аминов в спиртах существенно меньше этой величины для спиртов в аминах, причем для N-метилпиррола она положительная. Обсуждена природа такого поведения молекул в растворе. Рассчитаны энтальпии водородной связи аминов с кластерами спирта. Проанализировано влияние кооперативного эффекта на полученные значения. Hydrogen bond, one of the most important types of intermolecular interactions, has a strong influence on properties and reactivity of organic compounds in condensed phase. The net of hydrogen bonds determines the special physical properties of associated solvents (melt and boiling points, viscosity est.). Such solvents can be regarded as a mixture of associates different in structure and composition, which are in equilibrium with each other. The examples of such solvents are water, alcohols, amines etс. The interaction of associated solvents with various solutes has several features. Solvophobic effect, cooperativity and reorganization make the thermodynamic investigation of such interactions rather difficult. It was shown that interaction of proton acceptors with aliphatic alcohols consists of two steps: disruption of alcohol's associates and specific interaction with solute's molecule. The aim of this work is to investigate the specific interactions of aliphatic alcohols with aromatic amines (N-methylimidazole and N-methylpyrrol) and to find out how size of amine's ring and quantity of N-atoms in molecule can influence the thermodynamic parameters of hydrogen bonding. For comparison we used data obtained for pyridine. Firstly we compared pyridine, N-methylimidazole and N-methylpyrrol by their proton acceptor ability using specific interaction enthalpies with CHCl3. Chloroform is used as a standard proton donor with one acid H-atom in molecule. For calculation of specific interaction enthalpies we used Solomonov method. It is based on separation of solvation enthalpy into contributions of specific interactions and nonspecific solvation. Enthalpies of specific interaction with chloroform doubly increased going from N-methylpyrrol to N-methylimidazole, which is due to two activity centers in N-methylimidazole molecule. Size of amine ring also influences the proton acceptor properties. The specific interaction enthalpy of proton acceptor with associated alcohol differs from the enthalpy of formation of hydrogen bonded complexes stoichiometry one to one. On the one hand its value increases due to interaction of amines with cooperative complexes of alcohols. On the other hand this enthalpy decreases due to reorganization of solvent molecules. Thus, the value of specific interaction enthalpy is determined by two competing factors. The specific interaction enthalpies obtained for N-methylpyrrol and N-methylimidazole with alcohols are smaller than the enthalpies of specific interaction with chloroform, which confirms the suggested scheme. Because of two active N-atoms with lone pair in N-methylimidazole molecule, the specific interaction enthalpies of this amine with alcohols are larger than those of pyridine. Basing on the suggested scheme of complex specific interaction process we can also explain endothermic specific interaction enthalpies of N-methylpyrrol. Obviously, the endothermic term of solvent reorganization covers the exothermic enthalpy of cooperative hydrogen bonding. Assuming that the reorganization enthalpy is an association enthalpy with the opposite sign, we calculated the enthalpies of cooperative hydrogen bonding of N-methylpyrrol and N-methylimidazole with aliphatic alcohols. Its values increase from N-methylpyrrol and N-methylimidazole in accordance with their proton acceptor ability. |
| Databáze: | OpenAIRE |
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