碳氟键均裂解离能的密度泛函理论研究

运用6种密度泛函方法(B3LYP, B3P86, B3PW91, PBE1PBE, MPW1B95, MPW1K)对15个含氟有机化合物的碳氟键均裂解离能进行理论计算, 得到的理论值与实验值比较, 发现B3P86方法用于碳氟键均裂解离能的计算相对可靠. 使用验证后的理论方法对含氟杂环有机化合物和卤氟烃中的碳氟键均裂解离能进行了预测和分析, 并进一步讨论了α-取代基效应以及Hammett型取代基效应对碳氟键均裂解离能的影响.     

A computational study of C?S bond dissociation enthalpies in petroleum chemistry

High‐level theoretical methods (BMK, B3LYP, B98, B3P86, B3PW91, PBE1PBE, PBE1KIS, MPWPW91, MPW1KCIS, TPSS1KCIS, G3, G3//BMK, and CBS‐Q) were utilized to study the carbon–sulfur bond dissociation enthalpies (BDEs) of hydrocarbons in petroleum chemistry. The performance of these methods was evaluated on the basis of a training set including the available experimental BDEs, and it was found that the BMK (Boese‐Martin for Kinetics) method had the best agreement with experimental values. By using the BMK method to calculate C S BDEs of saturated hydrocarbon, the main factors, which determine the changing trend of BDE values, were discussed. Results revealed that the repulsive energies played an important role in determining a change in the trend of BDEs as well as the radical effect. Good agreements were obtained between further calculated BDEs and the experimental ones for C S and C O bonds. Moreover, the same calculation method was applied to predict C S BDEs for which the experimental values were still unavailable. A range of predicted bond dissociation enthalpy values were provided according to the calculations. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:97–105, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20662     

密度泛函法计算C1-C14正构烃生成焓及C-C键裂解能

采用密度泛函理论(DFT)方法研究了费托石脑油裂解反应中涉及到C₁-C₁₄正构烃和自由基中间体的生成焓及其C-C键解离能(BDE)。 结果表明,在所有评价的密度泛函理论方法（B97-1、BB1K、B1B95、MPWB1K和MPW1B95）中,MPW1B95/6-311G(d,p)方法计算最精确。 以此方法为基准,进一步对高碳烃及其裂解产物的标准生成焓和C-C键解离能进行了预测。 与可得到的实验数据相比,MPW1B95/6-311G(d,p)方法预测的烃和自由基的平均生成焓分别为0.8和2.7 kJ/mol,C-C键解离能的平均绝对误差只有3.1 kJ/mol,表明此方法不仅可准确计算正构烃标准生成焓和C-C键解离能,而且还能正确预测C-C键解离能变化趋势。     

O-H bond dissociation enthalpies in oximes: order restored

The O-H bond dissociation enthalpies (BDEs) of 13 oximes, RR'C=NOH, having R and/or R' = H, alkyl, and aryl are reported. Experimental anchor points used to validate the results of theoretical calculations include (1) the O-H BDEs of (t-Bu)2C=NOH, t-Bu(i-Pr)C=NOH, and t-Bu(1-Ad)C=NOH determined earlier from the heat released in the reaction of (t-Bu)2C=NO* with (PhNH)2 in benzene and EPR spectroscopy (Mahoney, L. R.; Mendenhall, G. D.; Ingold, K. U. J. Am. Chem. Soc. 1973, 95, 8610), all of which were decreased by 1.7 kcal/mol to reflect a revision to the heat of formation of (E)-azobenzene (which has significant ramifications for other BDEs) and to correct for the heat of hydrogen bonding of (t-Bu)2C=NOH (alphaH2 = 0.43 measured in this work) to benzene, and (2) the measured rates of thermal decomposition of six RR'C=NOCH2Ph at 423 or 443 K, which were used to derive O-H BDEs for the corresponding RR'C=NOH. Claims (Bordwell, F. G.; Ji, G. Z. J. Org. Chem. 1992, 57, 3019; Bordwell, F. G.; Zhang, S. J. Am. Chem. Soc. 1995, 117, 4858; and Bordwell, F. G.; Liu, W.-Z. J. Am. Chem. Soc. 1996, 118, 10819) that the O-H BDEs in mono- and diaryloximes are significantly lower than those for alkyloximes due to delocalization of the unpaired electron into the aromatic ring have always been inconsistent with the known structures of iminoxyl radicals as are the purported perpendicular structures, i.e., phi(Calpha-C=N-O*) = 90 degrees, for sterically hindered dialkyl iminoxyl radicals. The present results confirm the 1973 conclusion that simple steric effects, not electron delocalization or dramatic geometric changes, are responsible for the rather small differences in oxime O-H BDEs.     

Bond Dissociation Energies and Electronic Structures in a Series of Peroxy Radicals: A Theoretical Study

Quantum chemical calculations are performed to estimate the bond dissociation energies (BDEs) for 18 peroxy radicals. Since DFT methods are researched to have low basis sets sensitivity, these radicals are studied by utilizing the hybrid density functional theory (DFT) (B3LYP, B3P86, B3PW91 and PBE1PBE) in conjunction with the 6‐311G** basis set and the complete basis set (CBS‐Q) method. On the basis of comparisons of the computational results and the experimental values, we evaluate the effectiveness of above methods. It is demonstrated that CBS‐Q method is the best method for computing the reliable BDEs of C—OO bond, with the average absolute errors of 2.1 kcal/mol. So CBS‐Q method is suitable to predict accurate BDEs of C‐OO bond for peroxy compounds. The computational energy gaps between the HOMO and LUMO of studied compounds are almost identical from the point of view of stability and substantial HOMO‐LUMO gaps for all molecules suggest their electronic stability. In addition, substituent effect on the C—OO BDE of peroxy radicals is analyzed. It is noted that the effects of substitution on the C—OO BDE of peroxy radicals are significant. Our results will shed lights on future theoretical and experimental work.     

Electronic structures of 4d transition metal monoxides by density functional theory

Bond distances, dissociation energies, ionization potentials and electron affinities of 4d transition metal monoxides from YO to CdO and their positive and negative ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, SVWN, MPW1PW91 and PBE1PBE. It was found that calculated properties are highly dependent on the functionals employed, especially for dissociation energy. For most neutral species, pure density functionals BLYP, BPW91 and BP86 have good performance in predicting dissociation energy than hybrid density functionals B3LYP, B3PW91 and B3P86. In addition, BLYP gives the largest bond distance compared with other density functional methods, while SVWN gives shortest bond distance, largest dissociation energy and electron affinity. For the ground state, the spin multiplicity of the charged species can be obtained by ± 1 of their corresponding neutral species.     

Theoretical study of the vibrational frequencies of carbon disulfide

A benchmark comparison for different computational methods and basis sets has been presented. In this study, five computational methods (Hartree–Fock (HF), MP2, B3LYP, MPW1MP91, and PBE1PBE) along with 18 basis sets have been applied to optimize the geometry of carbon disulfide (CS₂), and further calculate the vibrational frequencies of the optimized geometries. The differences between the calculated frequencies and corresponding experimental data are used to evaluate the efficiency of each combination of computational method and basis set. The comparison of frequency difference indicates that B3LYP generally gives the best prediction of frequencies for CS₂, whereas the other two density functional theory (DFT) methods, i.e., MPW1PW91 and PBE1PBE, often give parallel results. Although MP2 predicts the frequencies with accuracy almost as good as those from DFT methods, in a particular case, HF calculation outperforms MP2 as well as MPW1PW91 and PBE1PBE for prediction of the frequency of asymmetrical stretching for CS₂. © 2013 Wiley Periodicals, Inc.     

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory

The C? NO₂ bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the C? NO₂ bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO₂ groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol^?1 from experimental ones for CH₂(NO₂)₂ and CH(NO₂)₃, when the diffusion functions are not augmented. For the C(NO₂)₄ molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electronic Structures of 5d Transition Metal Monoxides by Density Functional Theory

Bond distances, vibrational frequencies, electron affinities, ionization potentials, and dissociation energies of the diatomic 5d transition metal (except La) monoxides and their positively and negatively charged ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, MPW1PW91, PBE1PBE, and SVWN. Our calculation shows that for each individual species, the calculated properties are quite sensitive to the method used. Compared with hybrid density functional method B3PW91 (B3P86), pure density functional method BPW91 (BP86) gives longer bond distance (lower vibrational frequency) from HfO to PtO for neutral species, HfO⁺ to IrO⁺ for cationic species, and HfO⁻ to AuO⁻ for anionic species. While for B3LYP and BLYP, the trend was observed for cationic species from HfO⁺ to IrO⁺ and anionic species from HfO⁻ to AuO⁻ (except TaO⁻), but not for neutrals. Pure density function methods BLYP, BPW91, and BP86 give larger dissociation energy compared with hybrid density functional methods B3LYP, B3PW91, and B3P86. SVWN in most cases gives the smallest bond distance, while BLYP gives the largest value. MPW1PW91 and PBE1PBE show the same performance in predicting the spectroscopic constants. In addition, useful empirical criteria that one has obtained the ground states of a species and its ions are the spin multiplicities of a neutral and its single charged ions which differs by ±1.     

环境污染物中碳氯键离解能的理论研究

利用六种密度泛函理论方法（B3LYP, B3P86, MPW1K, TPSS1KCIS, X3LYP, BMK）对碳氯键离解能进行理论计算,结果发现几种新发展的密度泛函(DFT)方法用于碳氯键离解能的计算比传统的B3LYP有较大的改善,其中对能量估算相对准确的B3P86方法对碳氯键离解能的计算精度最高,对17个分子中碳氯键离解能计算的平均绝对偏差为6.58 kJ/mol。最后运用B3P86方法对一系列环境危害较大,但可通过光化学降解和生物降解的氯代有机物的碳氯键离解能值进行预测,并讨论了影响碳氯键离解能的结构性质关系。     

Dioxime oxalates; new iminyl radical precursors for syntheses of N-heterocycles

Symmetrical and unsymmetrical dioxime oxalates were prepared by treatment of oximes with oxalyl chloride. UV photolysis of these precursors was found to be an atom-efficient way of generating iminyl radicals. The process was most efficient for dioxime oxalates having aryl substituents attached to their CN bonds. The method was useful for EPR spectroscopic study of iminyl and iminoxyl radicals. Photolyses in toluene solution, of dioxime oxalates containing alkenyl acceptor groups, yielded unsaturated iminyl radicals that ring closed to afford 3,4-dihydro-2H-pyrroles in good yields. Dioxime oxalates with biphenyl substituents also released iminyl radicals that ring closed onto the aromatic acceptor groups and, in acetonitrile solution, this approach provided a useful and atom-efficient method of making substituted phenanthridines.     

Effects of geminal disubstitution on C-H and N-H bond dissociation energies

Composite ab initio methods including G3, CBS-Q, and G3B3 were used to calculate the C-H and N-H bond dissociation energies (BDEs) of a variety of disubstituted methane and ammonia molecules. The calculated BDEs were in excellent agreement with the available experimental data. Using these reliable BDEs we studied the effects of geminal disubstitution on C-H and N-H BDEs. It was found that the effects of the two substituents were not additive. Detailed separation of the substituent effects on BDEs to those associated with the parent molecules and those associated with the radicals was then performed using appropriate isodesmic reactions. It was found the geminal substitution effects on the stabilities of methanes, methyl radicals, amines, and amine radicals were all governed by five basic types of energetic effects, namely, hyperconjugation effect (stabilizing), electrostatic attraction (stabilizing) or repulsion (destabilizing), conjugation saturation effect (destabilizing), captodative effect (stabilizing), and steric effect (destabilizing). The conformations of the species played an essential role in determining whether a particular energetic effect could take place. Because the carbon-centered and nitrogen-centered species often had quite different conformational preferences, the geminal substitution effects on these two classes of species were quite dissimilar to each other.     

Bond dissociation energies for removal of the hydroxyl group in some alcohols from quantum chemical calculations

In this theoretical work, 22 alcohols and their geometric structure properties have been investigated employing quantum chemical methods to calculate the C? OH equilibrium bond distances and bond dissociation energies (BDEs). Since DFT methods have been researched to have low basis sets sensitivity for small and medium molecules in our previous work (Zhao et al., J Mol Struct, 2006, 766, 87), 22 title compounds have been studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86, PBE1PBE) in conjunction with the 6‐311G** basis set and the complete basis set (CBS–Q) method. Comparison with the available experimental data shows that CBS–Q and B3P86 methods calculated results agree very well with the experimental values, with the average absolute errors of 1.3 kcal/mol and 3.5 kcal/mol, respectively. So considering the expensive computational time, CBS–Q method can be chosen as a satisfactory method of predicting the accurate BDEs for removal of the OH group in small and medium size alcohols. And B3P86 method may give accurate BDEs for larger alcohols we haven't studied. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Effect of structure in benzaldehyde oximes on the formation of aldehydes and nitriles under photoinduced electron-transfer conditions

The mechanistic aspects of the photosensitized reactions of a series of benzaldehyde oximes (1a-o) were studied by steady-state (product studies) and laser flash photolysis methods. Nanosecond laser flash photolysis studies have shown that the reaction of the oxime with triplet chloranil (3CA) proceeds via an electron-transfer mechanism provided the free energy for electron transfer (DeltaG(ET)) is favorable; typically, the oxidation potential of the oxime should be below 2.0 V. Substituted benzaldehyde oximes with oxidation potentials greater than 2.0 V quench 3CA at rates that are independent of the substituent and the oxidation potential. The most likely mechanism under these conditions is a hydrogen atom transfer mechanism as this reaction should be dependent on the O-H bond strength only, which is virtually the same for all oximes. Product studies have shown that aldoximes react to give both the corresponding aldehyde and the nitrile. The important intermediate in the aldehyde pathway is the iminoxyl radical, which is formed via an electron transfer-proton transfer (ET-PT) sequence (for oximes with low oxidation potentials) or via a hydrogen atom transfer (HAT) pathway (for oximes with larger oxidation potentials). The nitriles are proposed to result from intermediate iminoyl radicals, which can be formed via direct hydrogen atom abstraction or via an electron-transfer-proton-transfer sequence. The experimental data seems to support the direct hydrogen atom abstraction as evidenced by the break in linearity in the plot of the quenching rates against the oxidation potential, which suggests a change in mechanism. The nitrile product is favored when electron-accepting substituents are present on the benzene ring of the benzaldehyde oximes or when the hydroxyl hydrogen atom is unavailable for abstraction. The latter is the case in pyridine-2-carboxaldoxime (2), where a strong intramolecular hydrogen bond is formed. Other molecules that form weaker intramolecular hydrogen bonds such as 2-furaldehyde oxime (3) and thiophene-2-carboxaldoxime (4) tend to yield increasing amounts of aldehyde.     

Trends in R-X bond dissociation energies (R = Me, Et, i-Pr, t-Bu; X = H, CH3, OCH3, OH, F): a surprising shortcoming of density functional theory

The performance of a variety of high-level composite procedures, as well as lower-cost density functional theory (DFT)- and second-order perturbation theory (MP2)-based methods, for the prediction of absolute and relative R-X bond dissociation energies (BDEs) was examined for R = Me, Et, i-Pr and t-Bu, and X = H, CH(3), OCH(3), OH and F. The methods considered include the high-level G3(MP2)-RAD and G3-RAD procedures, a variety of pure and hybrid DFT methods (B-LYP, B3-LYP, B3-P86, KMLYP, B1B95, MPW1PW91, MPW1B95, BB1K, MPW1K, MPWB1K and BMK), standard restricted (open-shell) MP2 (RMP2), and two recently introduced variants of MP2, namely spin-component-scaled MP2 (SCS-MP2) and scaled-opposite-spin MP2 (SOS-MP2). The high-level composite procedures show very good agreement with experiment and are used to evaluate the performance of the lower-level DFT- and MP2-based procedures. The best DFT methods (KMLYP and particularly BMK) provide very reasonable predictions for the absolute heats of formation and R-X BDEs for the systems studied. However, all of the DFT methods overestimate the stabilizing effect on BDEs in going from R = Me to R = t-Bu, leading in some cases to incorrect qualitative behavior. In contrast, the MP2-based methods generally show larger errors (than the best DFT methods) in the absolute heats of formation and BDEs, but better behavior for the relative BDEs, although they do tend to underestimate the stabilizing effect on BDEs in going from R = Me to R = t-Bu. The potentially less computationally expensive SOS-MP2 method offers particular promise as a reliable method that might be applicable to larger systems.     

A DFT conformational analysis and VCD study on methyl tetrahydrofuran-2-carboxylate

DFT calculations were performed on (S)-methyl tetrahydrofuran-2-carboxylate to facilitate the interpretation of IR and VCD spectra. The potential energy surface could not be described unambiguously using the 6-31G* basis set in combination with different density functionals including B1LYP, B3LYP, B3P86, B3PW91, B98, BHandH, BHandHLYP, MPW1PW91 and PBE1PBE. In contrast, a uniform conformational picture could be found using the cc-pVTZ basis set. Using this large basis set and the collection of nine functionals from above, the dipole and rotational strengths were calculated, and compared to experimental values which were extracted from the experimental IR and VCD spectra for (+)-(S)-methyl tetrahydrofuran-2-carboxylate. A detailed analysis on the agreement between experiment and simulated spectra was performed by assigning the experimental bands based on the harmonic fundamentals obtained for all functionals except BHandH, which performs badly over the whole line. Assessing the dipole strengths, all tested functionals perform equally well. For the rotational strengths, differences can be observed: B3LYP, B1LYP and B98 give the highest correlation with experiment, while PBE1PBE gives the lowest correlation. Comparable conclusions are obtained using a neighborhood similarity measure.     

Electronic effects on O-H proton dissociation energies of phenolic cation radicals: a DFT study

The electronic effects on O-H proton dissociation energies (PDEs) of para- and meta-substituted phenolic cation radicals have been investigated by density functional theory (DFT) using B3LYP function on a 6-31G(d, p) basis set. The calculation results indicate that electron-donating groups raise the O-H PDE and electron-withdrawing groups reduce the parameter, which are opposite to the electronic effects on O-H bond dissociation energies (BDEs). In addition, the electronic effects on O-H PDE are much stronger than those on O-H BDE. The differences result from the distinct electronic effects on stabilities of phenolic cation radicals and parent phenols. The finding also implies the proton-transfer process is unlikely a rate-controlling step for phenolic antioxidants to scavenge free radicals. Moreover, like O-H BDE, O-H PDE correlate better with the resonance parameter R+ than with field/inductive parameter F. Therefore, O-H PDEs of para-substituted phenolic cation radicals are mainly governed by the resonance effect.     

Multilevel and density functional electronic structure calculations of proton affinities and gas-phase basicities involved in biological phosphoryl transfer

Five multilevel model chemistries (CBS-QB3, G3B3, G3MP2B3, MCG3/3, and MC-QCISD/3) and seven hybrid density functional methods (PBE0, B1B95, B3LYP, MPW1KCIS, PBE1KCIS, and MPW1B95) have been applied to the calculation of gas-phase basicity and proton affinity values for a series of 17 molecules relevant to the study of biological phosphoryl transfer. In addition, W1 calculations were performed on a subset of molecules. The accuracy of the methods was assessed and the nature of systematic errors was explored, leading to the introduction of a set of effective bond enthalpy and entropy correction terms. The multicoefficient correlation methods (MCG3/3 and MC-QCISD), with inclusion of specific zero-point scale factors, slightly outperform the other multilevel methods tested (CBS-QB3, G3B3, and G3MP2B3), with significantly less computational cost, and in the case of MC-QCISD, slightly less severe scaling. Four density functional methods, PBE1KCIS, MPW1B95, PBE0, and B1B95 perform nearly as well as the multilevel methods. These results provide an important set of benchmarks relevant to biological phosphoryl transfer reactions.     

Density Functional Calculations of C-NO2 Bond Dissociation Energies for Nitroalkanes Molecules

Bond dissociation energies for the removal of nitrogen dioxide group in some nitroalkane energetic materials have been calculated by using the three hybrid density functional theory （DFT） methods B3LYP, B3PW91 and B3P86 with 6-31g^＊＊ and 6-311g^＊＊ basis sets. The computed BDEs have been compared with the available experimental results. It is found that the B3P86 method with 6-31g^＊＊ and 6-311g^＊＊ basis sets can obtain satisfactory bond dissociation energies （BDEs）, which are in extraordinary agreement with the experimental data. Considering the smaller mean absolute deviation and maximum difference, the reliable B3P86/6-311g^＊＊ method was recommended to compute the BDEs for the removal of nitrogen dioxide group in the nitroalkane energetic materials. Using the method, the BDEs of 8 other nitroalkane energetic materials have been calculated and the maximum difference from experimental value is 1.76 kcal.mo1^-1 （for the BDE of tC4Hg-NOz）, which further proves the reliability of B3P86/6-311g^＊＊ method. In addition, it is noted that the BDEs of C-NO2 bond change slightly for main chain nitroalkane compounds with the maximum difference of only 3.43 kcal mo1^-1.