草酸及其離子之理論研究

Theoretical Study of Oxalic Acid and Its Anions

10.6623/chem.1997016

陳世忠(Shyh-Jong Chen)；陳成(Cheng Chen)

幾何優選 ； 內轉動能之過渡態結構 ； 區域化氯鍵 ； 官能基間氫鍵 ； 官能基內氫鍵 ； Geometry Optimization ； Transition States of Internal Rotation ； Localized Hydrogen Bond ； Inter-Functional Group Hydrogen Bonds ； Inter-Functional Group Hydrogen Bonds

化學

55卷2期（1997 / 06 / 01）

19 - 36

繁體中文

以MP2/6-31G**//MP2/6-31G** ab initio法對草酸及其離子作幾何優選及頻率、零點能修定計算研究。吾等由草酸(COOH)_2找到六個穩定態結構及八個內轉動能之過渡態結構；草酸離子(COOH) COO-有二個穩定態結構及三個內轉動能之過渡態、(COO)2^(-2)有一個穩定態結構及一個內轉動能之過渡態結構，且所有穩定態結槽計算之頻率均為正值：內轉動能之過渡態結構計算結果均有一個負頻率。另從吾等近年提出之區域化氫鍵理論，以s-p INDO分子軌域法計算其草酸及其離子結構之區域氫鍵鍵能及區域鍵次，證實草酸分子結構之穩定，其分子內氫鍵中官能基間氫鍵較官能基內氫鍵重要。另取參考文獻電子繞射實驗值之幾何結構資料進行相同之鍵能、鍵次計算比對，證實官能基間存在較強之氫鍵係織成結構穩定之重要因素與ab initio法計算能量結果相同，另草酸負一價離子(COOH) COO' 發現較直在酸其他結構有一最強之官能基間氫鍵是以往文獻中所未發現。

The ab initio MP2/6-31G** method has been carried out for theoretical calculation studying on geometry optimization and vibrational frequency types calculation of oxalic acid and its anions. We found six local minima and eight transition states of internal rotation for oxalic acid (COOH)_2; two local minima and two transition states of internal rotation for oxalic acid ion (COOH)COO'; and one local minimum and transition states of internal rotation for oxalic acid diion (COO)_2^(-2). All the calculated local minima are proved to have real and positive value frequencies, and the transition states of internal rotation are proved to have one imaginary frequency only in each case. We applies the Sop INDO MO type localized hydrogen bond analysis method which developed by us recently to analysis the ＂localized hydrogen bond energy＂ and ＂localized hydrogen bond order＂ of the various conformers of oxalic acid (COOH)_2 and its (COOH)COO' anion. With this type oflocalized analysis the hydrogen bonding strength and the related molecular stabilities of various conformers are compared. We found that the inter-function group hydrogen bonding is more important than the intra-function group hydrogen bonding in this molecular systems. We selected the observed geometrical data from the experimental reference for our Sop INDO MO and hydrogen bonding analysis, we found the inter-function group hydrogen bonding in oxalic acid is more stronger effect than which predicted by ab initio method, In (COOH)COO' anion case, inter-function group hydrogen bonding is very strong was first predicted by this work and which was never been reported by any former references.