- 期刊
氧態分子酸度之理論研究
Theoretical Sutdy on the Acidity of Gas-Phase Molecules
摘要
氣態分子酸度沒有溶劑介質影響，可視為絕對酸度。以理論計算值與文獻實驗值比較後，Gausssian 98套裝軟體的B3LYP/6-311++G(3df,2pd)、B3LYP/6-311+G(2d,p)與CBS-QB3的計算方法相對標準差均小於2%，顯示這三個計算方法的準確度值得信賴，羧酸類的分子具有syn與anti兩種構形異構物，anti構形計算所之數據較接近文獻之實驗測得之值。酸度受到羧基上的原子團性質影響，推電子基與拉電子基對羧基上π電子的作用影響羧酸的酸度。氟原子為特別強的拉電子基，氟的加入使分子自由能下降約50-100kj/mol有明顯提昇分子酸度的作用。
並列摘要
The acidity of gas-phase molecules, without being affected by the solvent, can be deemed as an absolute acidity. After compared the values both being calculated theoretically and experimentally, the relative standard deviations as found herein, which are gained through the application of B3LYP/6311++ G(3df,2pd), B3LYP/6-311+G(2d,p) amCBS-QB3 provided by the Gaussian 98 package software, are less than 2%. Obviously, the accuracy of the three methods of calculation is more reliable. Carboxylic acids exist in two forms, that is, syn conformers and anti conformers. The result of calculation shows that the calculated value of anti conformer is closer to the experimented value. Because the acidity is affected by the nature of substitution group in the carboxyl group, as a result, the delocalization interaction of electron-withdrawing and electron-releasing substituents on the π electron in the carboxyl group affected the acidity of carboxylic acids. Fluorine atom has a stronger electron-withdrawing effect, and the molecules with fluorine may reduce Gibbs energy about at 50-100 kJ/mol and substantially promote the acidity of molecules.