【摘要】 用X3LYP法在6-311++G(d,p)和6-311++G(3df,3pd)基组水平上对脯氨酸15种构象的几何结构、相对能量、电子结构、红外光谱、偶极矩、极化率等性质进行了研究,并与PBE1PBE/6-311++G(d,p)的结果和文献相比较,从而得到:(1)的脯氨酸的15种构象中能量最低的有4种,不同构象中存在着强弱不同的5种氢键,其中以N…H—O氢键最强,并存在特殊的C—H…O＝C氢键.两种方法计算的几何结构数据相近,均与实验值吻合;(2)在构象相对能差计算方面,X3LYP具有明显的优势,用中等基组就可以得到与高水平从头算法和大基组相同的结果,而PBE1PBE法计算的相对能值则相差较大;(3)脯氨酸不同构象中偶极矩最大和极化率最小的是最稳定的构象1和2,两种方法计算的结果一致.更多还原

【Abstract】 A total of 15 conformers of proline were found and their geometrical structures,relative energies,harmonic frequencies,dipole moments,rotational constants,polarizabilities,and the difference in energies between HOMO and LUMO were calculated at the X3LYP/6-311++G(d,p)and the PBE1PBE/6-311++G(d,p)levels.Accurate relative energies were given at the X3LYP/6-311++G(3df,3pd)//X3LYP/6-311++G(d,p)level of theory,which were in good agreement with high-level ab initio methods using large basis sets.The results of X3LYP are superior to those of PBE1PBE method.The characteristic H-bonding types for all the conformers were classified.The four most stable conformers had intramolecular H-bondings of N...H-O and N-H...O=C,and the dipole moments of conformers 1 and 2 were the largest and the polarizabilities were the smallest.An additional H-bonding C-H...O=C was found.In combination with the principles of statistical mechanics,conformational distributions at room temperature were computed.更多还原