特丁基对苯二酚的光谱及密度泛函研究

特丁基对苯二酚是重要的食品抗氧化剂.理论上,基于密度泛函理论,采用B3LYP泛函及6-311G(d,p)基组在气相环境下优化分子的结构并进行频率计算.在此基础上,基于含时密度泛函理论,选用SMD(solvation model based on density)溶剂模型,利用B3LYP泛函并结合def2-TZVP基组计算分子在无水乙醇溶剂中的前50个激发态.再通过Multiwfn软件对红外光谱做振动分析并考察分子间相互作用对红外光谱的影响,对紫外光谱做分子轨道和电子空穴分析.实验上,通过KBr压片法,利用傅里叶红外变换光谱仪测定样品红外光谱.采用液相法,以乙醇为溶剂,利用紫外可见分光光度计测定样品紫外光谱.通过对比分析可知,理论光谱与实验光谱总体吻合较好.红外光谱各基团的特征吸收峰都较为明显且较好吻合,特丁基对苯二酚二聚体存在氢键作用,这使得O—H键的强度被削弱,导致吸收频率降低并在3670—3070 cm^-1处出现一个宽峰.紫外光谱主要由基态跃迁至第1,2,6,7激发态形成,最大吸收峰位于200 nm以下,为π→π^*和s→π^*跃迁形成,268.8 nm和221.4 nm处的吸收峰均为n→π^*和π→π^*跃迁形成.由电子空穴图可知,这4个主要激发均为电子局域激发.

Spectral analysis and density functional theory study of tert-butylhydroquinone

Tert-butylhydroquinone(TBHQ)is an important food antioxidant.Based on density functional theory,the B3LYP functional is used to optimize the geometric configuration and calculate the frequency of TBHQ molecule in gas phase at a level of 6-311g(d,p)basis set.On this basis,based on the time-dependent density functional theory,SMD implicit solvent model is selected,and the first 50 excited states of molecule in ethanol solvent are calculated by using B3LYP functional and def2-TZVP basis set.Multiwfn software is used to analyze the vibration of IR spectrum,the influence of interaction among molecules on IR spectrum and the molecular orbital and electron-hole of UV spectrum.Experimentally,Fourier transform infrared spectrometer(FTIR)is used to measure the IR spectrum of TBHQ sample by KBr tablet method.The UV spectrum of the sample determined in the ethanol solvent by ultraviolet visible spectrophotometer.By comparative analysis,it can be seen that the theoretical spectra are in good agreement with the experimental spectra.The characteristic absorption peaks of each group in the IR spectra are obvious,and the theoretical peaks are in good agreement with the positions of the measured peaks.The hydrogen bonding of dimers and polymers in the TBHQ sample can weaken the O—H bond strength of a single molecule,thus weakening the vibration frequency of the O—H bond and resulting in a wide peak at 3670–3070 cm^-1 in the experimental IR spectrum.The UV spectra are mainly formed from the ground state to the first,second,sixth and seventh excited state.The maximum absorption peak in the UV spectrum is below 200 nm and is formed by the transitions ofπ→π^*and s→π^*.The absorption peaks at 268.8 nm and 221.4 nm are formed by the transitions of n→π^*andπ→π^*.It can be seen from the electron-hole distribution diagram that these four excitations are all electron local excitation.This study may play a certain role in understanding the molecular structure and excitation properties of TBHQ,as well as the formation mechanism of its IR and UV spectra,and also conduce to understanding its antioxidant properties.