氟、氯和甲基取代丁二酰亚胺的结构、红外光谱和热力学性质的密度泛函理论研究

Studies on the Structures, Infrared Spectra and Thermodynamic Properties of NFluo, NChloro and NMethylsuccinimide by Using Density Functional Method

用密度泛函理论（ＤＦＴ）的Ｂ３ＬＹＰ方法（６－３１Ｇ＊基组），计算研究了丁二酰亚胺（ＳＩＭ）的氟、氯和甲基取代物（ＳＩＭＦ，ＳＩＭＣｌ和ＳＩＭＭｅ）的几何构型、电子结构、红外光谱和热力学性质，讨论了取代基效应．结果表明，ＳＩＭＦ和ＳＩＭＣｌ均为平面构型，ＳＩＭＭｅ接近平面构型．羰基伸缩振动频率（νＣ＝Ｏ）均分裂为两个谱带，低频带出现在１７３４～１７７１ｃｍ－１，高频带出现在１７９２～１８２２ｃｍ－１，且前者强于后者．与ＳＩＭ相比，吸电子基（Ｆ和Ｃｌ）使νＣ＝Ｏ和偶极矩增大，推电子基（ＣＨ３）的影响正相反．由校正频率计算了２９８～８００Ｋ温度范围的热力学性质熵（Ｓ°）和热容（Ｃｐ°）．

Density functional theory(DFT) with the B3LYP method and 631G* basis set has been employed to investigate the geometries, electronic structures, infrared spectra and thermodynamic properties of Nfluo, Nchloro and Nmethylsuccinimide(abbreviated as SIMF, SIMCl and SIMMe, respectively) in gasphase, the effect of substituents on the above properties is discussed. It is shown that SIMF and SIMCl are planar, SIMMe is essentially planar. The C=O stretch vibration(C=O) splits into two bands at 1 7341 771 and 1 7921 822 cm-1 respectively, and the low frequency band has much stronger intensity than the high one. Compared with SIM, electron withdrawing group(F or Cl) makes the C=O and dipole moment larger, while electron contributing group has an opposite effect. The standard thermodynamic functions, i.e., entropy(S) and heat capacity(Cp), have been derived with the scaled computed frequencies.