The gas phase reaction mechanism of Cl2 + I2 = 2ICl has been theoretically investigated by DFT method at the B3LYP/3-21G* level. Transition states of three reaction channels were consequently given. The results indicate that in the title reaction the least activation energy of bi-molecular reaction was smaller than the dissociation energies of I2 and Cl2, and thus the reaction mechanism was the course of molecule-molecule interaction at low reaction rate. If other factors such as illumination were taken into account, I2 could dissociate into I atoms and then react with Cl2, or Cl2 dissociates into Cl atoms and reacts with I2. These were photochemical reactions with high reaction speed. The theoretical results were further validated with absorbance measurement at 516 nm.
YANG Guo-YingYUAN Li-XiaSUN De-ShengWANG Zun-YaoJIANG Tao
Optimization calculations of 209 polychlorinated biphenyls (PCBs) were carried out at the B3LYP/6-31G* level. It was found that there is significant correlation between the Cl substitution position and some structural parameters. Consequently, Cl substitution positions were taken as theoretical descriptors to establish a novel QSPR model for predicting –lgS_w of all PCB congeners. The model achieved in this work contains four variables, of which r2 = 0.9527, q2 = 0.9490 and SD = 0.25 with large t values. In addition, the variation inflation factors (VIFs) of variables in this model are all less than 5.0, suggesting high accuracy of the –lgS_w predicting model. And the results of cross-validation test and method validation also show that the model exhibits optimum stability and better predictive capability than that from the AM1 method.
Optimized calculations of 75 PCDDs and their parent DD were carried out at the B3LYP/6-31G* level by density functional theory (DFT) method. The structural parameters were obtained and significant correlation between the Cl substitution position and some structural parameters was found. Consequently, the number of Cl substitution positions was taken as theoretical descriptors to establish two novel QSPR models for predicting lgKow and –lgSw of all PCDD congeners. The two models achieved in this work contain two variables (Nα and Nβ), of which r = 0.9312, 0.9965 and SD = 0.27, 0.12 respectively, and t values are all large. The variation inflation factors (VIF) of variables in the two models herein are both less than 5.0, suggesting high accuracy of the lgKow and –lgSw predicting models, and the results of cross-validation test also show that the two models exhibit optimum stability and good predictive power. By comparison, the correlation and predictive ability of the present work are more advantageous than those obtained using semi-empirical AM1 and GC-RI methods.
Molecular property parameters of 16 2-formamido-phenylacrylates were calculated with Hartree-Fock and DFT methods at six different levels. Using the molecular property para- meters and dissolvability as theoretical descriptors, two quantitative correlation equations that could be used to predict lgKow were developed based on experimental lgKow data of 11 2-formami- do-phenylacrylates. A three-parameter correlation equation posing the ability of predicting –lgSw value was computed at B3LYP/6-311G** level. The –lgSw values of five compounds that we have pre-designed were anticipated with the above equation, upon which lgKow were further calculated. The relativity (r2≥0.94, q2>0.91, SD≤0.083) and prediction ability of obtained correlation equa- tions in this work are more advantageous than those based on solvatochromism parameters.
Phenylthio-carboxylates were computed at the B3LYP/6-31G* level with DFT method. Based on linear solvation energy theory, the structural parameters were firstly taken as theoretical descriptors, and the corresponding linear solvation energy relationship (LSER) equation (r = 0.8989) to the toxicity of photobacterium phosphoreum (–lgEC50) was thus obtained. Then the structural and thermodynamic parameters were taken as theoretical descriptors, and as a result the other corresponding correlation equation (r = 0.9274) relating to –lgEC50 was provided. The two equations achieved in this work by B3LYP/6-31G* are both more advantageous than that from AM1.
The gas phase reaction mechanism of F2 + 2HBr = 2HF + Br2 has been investigated by (U)MP2 at 6-311G** level, and a series of four-center and three-center transition states have been obtained. The reaction mechanism was achieved by comparing the activation energy of seven reaction paths, i.e. the dissociation energy of F2 is less than the activation energy of the bimolecular elementary reaction F2 + HBr → HF + BrF. Thus it is theoretically proved that the title reaction occurs more easily in the free radical reaction with three medium steps.
