丙烯醯胺之分子間作用力與振動光譜的量子化學計算

Abstract

進行量子化學理論計算時，我們使用Gaussian09軟體，以MP2/6-311++G**、MP2/aug-cc-pVTZ計算C3H5NO(丙烯醯胺)的單體最佳化結構。得到單體最佳化結構後，接著以順式丙烯醯胺及反式丙烯醯胺交互形成十二種二聚體，以微擾理論(Moller-Plesset perturbation theory ，MP)來進行丙烯醯胺二聚體間的分子作用力計算，使用基底最高到6-311++G(3df,3pd)及aug-cc-pVTZ，其中均加入了BSSE修正，以探討鍵結距離，氫鍵、凡德瓦力的能量大小，以及頻率變化。計算單體得到的IR光譜，由高波數區域(4000~1500 cm-1)得到丙烯醯胺分子中的官能基頻率及振動型態；由低波數區域(1500~0 cm-1)得到丙烯醯胺本身特有的振動頻率(主要由C-C構成)。若比較單體及雙體的吸收光譜，由不同頻率的紅藍移和強度變化，可以分析出各種不同構型間的鍵結類型(如：凡得瓦力、氫鍵)。與實驗值的比較，可以發現二聚體可能的過渡態及不同的轉換型態，推斷是否有質子轉移的可能性。 接著使用密度泛函理論(Density functional theory ，DFT)來計算丙烯醯胺雙體結構。我們採用了17種不同的DFT(M05、M052X、M06、M062X、M06L、B97D、wB97X、wB97XD、B3LYP、CAM-B3LYP、X3LYP、mPW1PBE、mPW3PBE、LC-wPBE、HSEH1PBE、B2PLYP、B2PLYPD)，將所得的計算結果與MP2做比較，找出最適合雙氫鍵結構的DFT。

All the quantum chemistry calculations were performed at the MP2 level of theory using the Gaussian 09 program package. The isolated C3H5NO molecule was first optimized at the aug-cc-pVTZ and 6-311++G** level. After the optimization of monomer, intermolecular interaction potentials of the acrylamide dimer in 12 orientations have been calculated using the second-order Moller-Plesset (MP2) perturbation theory. We have employed pople’s medium size basis sets [up to 6-311++G(3df,3pd)], Dunning’s correlation consistent basis sets (up to aug-cc-pVTZ) and the correction of the basis-set superposition error(BSSE) to explore the bonding distance, hydrogen bonding, van der Waals force, and vibration. IR spectrum calculated by monomers can be obtained the functional groups in the molecule from high wavenumber region (4000 ~ 1500 cm-1), and vibration types from low wavenumber region (1500 ~ 0 cm-1)(mainly constituted by the CC). When comparing the vibration spectrum of the monomer and the dimer, we can analyze different types of bonding from the different frequency shift and the intensity (such as: van der Waals forces, hydrogen bond). To compare with the experimental values can find possible transition states and different conversion types of dimer, to infer whether there is the possibility of proton transfer. We also have carried out 17 methods of the Density Functional theory(DFT) (M05、M052X、M06、M062X、M06L、B97D、wB97X、wB97XD、B3LYP、CAM-B3LYP、X3LYP、mPW1PBE、mPW3PBE、LC-wPBE、HSEH1PBE、B2PLYP、B2PLYPD)calculations, and then compared with the results of MP2.