Barrier ΔE Research Articles

Understanding into interfacial properties and reactivity of COFs toward accelerating Menshutkin SN2 reaction

Given the poor understanding about the effects of confined polar microenvironment on interfacial behaviors of Menshutkin SN2 reaction, herein, the interfacial properties and reactivities between 1-methylimidazole and methyl thiocyanate reaction induced by interfacial polar microenvironments of covalent organic frameworks (COFs) with varying pore size and functional groups were investigated using in situ Fourier transform infrared spectroscopy, molecular dynamics simulations, and metadynamics calculations. The decreased nanopore size of COFs from 3.2 to 1.2 nm can enlarge reaction rates (k) and reduce activation energy barriers (ΔE*). The hydroxyl-modified COF (2.8 nm) can further cause larger k and lower ΔE* by 6.1 and 0.8 kJ/mol compared to the bulk and smaller pore-size COF (1.2 nm) system, respectively, mainly originating from induced higher aggregation, preferred orientation, and the stabilization of charge separation of transition state. This work provides a systematic understanding for the confined interfacial properties toward accelerating the Menshutkin reaction.

Molecular Origin of the Reinforcement Effect and Its Strain-Rate Dependence in Polymer Nanocomposite Glass.

We investigate the molecular origin of mechanical reinforcement in a polymer nanocomposite (PNC) under a glass state via molecular dynamics simulations. The strength of the PNC system is found to be reinforced mainly via reduced plastic deformations of the nanoparticle neighborhood (NN). Such a reinforcement effect is found to decay with an increase in the strain rate. The Arrhenius-Eyring relation is used to analyze its origin. The amplitude of the reinforcement is found to be determined by the difference between the energy barrier (ΔE) for the activation of NN and the work (W) done by the applied stress to conquer that barrier. A larger strain rate is found to result in a larger W and, hence, a weaker reinforcement effect. Such a strain-rate dependence is verified in the experimental tensile tests of a poly(vinyl alcohol)/SiO2 composite system. These results not only provide a new understanding of the molecular origin of the reinforcement effect in the PNC system, but also pave the way for a better design of the PNC material properties.

Effects of cations on rare earth adsorption and desorption in binding sites of montmorillonite

The exchangeability of rare earth (RE) in weathered crust elution-deposited rare earth ores largely depends on its interaction with clay minerals, which may be significantly influenced by various cations. Therefore, the effects of K<sup>+</sup>, Ca<sup>2+</sup> and Al<sup>3+</sup> on RE<sup>3+</sup> adsorption and desorption in binding sites of montmorillonite (MMT) were investigated. Through the pre-saturation, the interlayer ions of MMT had been replaced by K<sup>+</sup>, Ca<sup>2+</sup> or Al<sup>3+</sup>. RE<sup>3+</sup> can adsorb on the interlayer sites of Ca-MMT and K-MMT, but nearly not Al-MMT. The basal spacing of Ca-MMT is larger than K-MMT, which provides a smaller hinder effect of interlayer collapse for the interlayer diffusion of RE<sup>3+</sup>. The adsorption capacity followed the order: Ca-MMT＞K-MMT＞Al-MMT and La<sup>3+</sup>＞Y<sup>3+</sup>＞Eu<sup>3+</sup>. It can predict that the grade of the exchangeable RE in ores abundant in Ca<sup>2+</sup> is the most, followed by the ore rich in K<sup>+</sup> and Al<sup>3+</sup> the least. Clay minerals tend to adsorb light RE and hard to adsorb middle and heavy RE. The reversibility of RE adsorbed in interlayers, especially in collapsed interlayers, is far worse than that on externals. The desorption rates of RE were in the order of RE-Al-MMT＞RE-K-MMT＞RE-Ca-MMT and Eu<sup>3+</sup>＞Y<sup>3+</sup>＞La<sup>3+</sup>. For the desorption of interlayer RE<sup>3+</sup>, NH<sup>4+</sup> is better than Mg<sup>2+</sup> because the larger change of the basal spacings (Δd) provides more minor activation energy barriers (ΔE) for NH<sup>4+</sup> diffusion within interlayers. It can enrich the metallogeny theory of weathered crust elution-deposited rare earth ores and provide a certain theoretical basis for its efficient exploitation.

Assessing the Accuracy of Density Functional Approximations for Predicting Hydrolysis Reaction Kinetics.

Hydrolysis reactions are ubiquitous in biological, environmental, and industrial chemistry. Density functional theory (DFT) is commonly employed to study the kinetics and reaction mechanisms of hydrolysis processes. Here, we present a new data set, Barrier Heights for HydrOlysis - 36 (BH2O-36), to enable the design of density functional approximations (DFAs) and the rational selection of DFAs for applications in aqueous chemistry. BH2O-36 consists of 36 diverse organic and inorganic forward and reverse hydrolysis reactions with reference energy barriers ΔE‡ calculated at the CCSD(T)/CBS level. Using BH2O-36, we evaluate 63 DFAs. In terms of mean absolute error (MAE) and mean relative absolute error (MRAE), ωB97M-V is the best-performing DFA tested, while MN12-L-D3(BJ) is the best-performing pure (nonhybrid) DFA. Broadly, we find that range-separated hybrid DFAs are necessary to approach chemical accuracy (0.043 eV). Although the best-performing DFAs include a dispersion correction to account for long-range interactions, we find that dispersion corrections do not generally improve MAE or MRAE for this data set.

An investigation of CO2 conversion capacity for PCN series doped with different 3d ions (Fe2+, Co2+ and Cu2+)

Three porphyrinic Zr-MOFs (PCN-222, PCN-224 and PCN-226) doped with transition metals (Fe2+, Co2+ and Cu2+) are investigated for the potential application in carbon neutral, including the CO2 capture and conversion capacity as well as the stable cyclicity in the changeable environment. Based on the obtained structure properties, the adsorption quantities of CO2 and adsorption energies of the active sites (Fe2+, Co2+ and Cu2+) are calculated for the three PCN systems. As for the conversion capacity of these PCNs, the entire reduction pathway from CO2 to CH4 via an eight-electron transfer process is depicted by calculating the free energy (ΔG) and the energy barrier (ΔE), which can be modified by the different 3d ions doping. From the high separation efficiency of the products (CH4/CO2) and stability (thermostability in high temperature), the recyclability of these PCN is ultimately evaluated and found favorable for the industrial utilization. Therefore, the present work significantly supports that transition metals doping in different MOFs could yield the promising carbon capture and utilization (CCU) properties.

A corrected benzene nitration three-step mechanism derived by DFT calculation and MO theory

Density-functional theory (DFT) calculations at the LC-wHPBE/6-311++G(d,p) level found that the textbook three-step nitration mechanism of benzene in mixed acids was seriously wrong. Step 1 of generating nitronium ion (NO2+) is not spontaneous, the NO2+ is generated by Lewis collision, and needs to overcome a barrier Ea = 18 or 22 kcal/mol in mixed acid or in nitric acid. Obtaining the Ea of the Lewis collision by quantum chemical calculations is a highlight of the study. The reaction system (NO2+ + H2O) + HSO4⎺ or + NO3⎺ or + nH2O (n ≥ 1) can make NO2+ spontaneously change to HNO3 through a poly(≥3)-molecular acidification. Sulfuric acid can greatly reduce [H2O] and increase [NO2+]. Therefore, the nitration rate in mixed acid is much faster than that in nitric acid. Step 2, C6H6 + NO2+, is an electrophilic addition, follows the transition state theory, and needs to overcome a low barrier, ΔE* = 7 kcal/mol. The product of Step 2 is the σ-complex C6H6-NO2+. The essence of the electrophilic addition is the transfer of HOMO-1 electrons of C6H6 to LUMO of NO2+. Step 3 is a spontaneous Lewis acid-base neutralization without any barrier, and generates the target product nitrobenzene C6H5NO2. NO2+ and σ-complex are the two active intermediates in nitration. The benzene nitration rate control step is not Step 2 of generating σ-complex, but is Step 1 to generate NO2+. The DFT calculation obtains the barriers Ea and ΔE*, the reaction heats ΔHσ and ΔHp of each step of the nitration, resulting in the total nitration reaction heat ΔH = -35 kcal/mol. It is consistent with the experimental ΔH = -34 kcal/mol. Based on the results, a corrected benzene nitration three-step mechanism proposed.

First principles study of BC7 monolayer compared to graphene as an ultra-high-capacity sheet for hydrogen storage applications

In our attempt to find the best hydrogen storage, we thought of improving carbon-based materials, including creating a new compact material with graphene films. Compared to graphene, BC 7 improved the electronics, transport and storage properties of graphene. It increased the binding energy of graphene to a value of 0.2081 eV, with the most stable distance of 3.40 Å. The diffusion energy of the H 2 molecule on the substrate is about 2.25 meV. Our 2D material is capable of adsorbing 11 H 2 molecules with a gravimetric capacity (GC) up to 10.40 wt%. The adsorption/release temperature is about 177.00 K. These results prove that our material can be suitable for reversible hydrogen storage. • The adsorption energy around −0.2081 eV • The gravimetric capacity up to 10.40 wt% • The desorption temperature up to 177.00 K • The diffusion barriers ΔE barr about 2.25 meV

A DFT and molecular docking study of xerantholide and its interaction with Neisseria gonorrhoeae carbonic anhydrase

Xerantholide is a sesquiterpene lactone that has anti-gonorrhea and anti-plasmodium activities. We present gas-phase electronic structure calculations of the equilibrium geometry of xerantholide, its adiabatic electron affinity (AEA), adiabatic ionization energy (AIE) and the energy barrier (ΔE‡) connecting the lowest energy conformers of the sesquiterpene. The computations were performed with the B3LYP, M06-2X and ωB97xd variants of the density functional theory (DFT) in conjunction with large basis sets. With the inclusion of the vibrational zero point energy, the computed AEA range from 0.740 eV [B3LYP/Aug-CC-pVTZ] to 0.774 eV [B3LYP/6-311++G(d,p)], and the AIE is roughly 8.6 eV at all theoretical levels. At the B3LYP/Aug-CC-pVTZ level, the barrier (ΔE‡) connecting the two lowest energy conformers is predicted to be 13.9 kcal/mol. Based on the molecular docking analysis, xerantholide interacts with the active site of Neisseria gonorrhoeae carbonic anhydrase (NgCA) via hydrogen bonding, metal-acceptor interaction, and non-polar alkyl and pi-alkyl interactions. The predicted binding affinity of − 6.8 kcal/mol compares well with those obtained for standard NgCA inhibitors such as acetazolamide (−5.7 kcal/mol). A biomimetic model study involving xerantholide and zinc-tris imidazole ([ZnIm3]2+) ion was also carried out at different theoretical levels to estimate the interaction energy for the formation of the complex formed between the ligand and the active site model of NgCA. The binding free energy (ΔG) has been calculated to be − 28.5 kcal/mol at the B3LYP/6-311++G(d,p) level. The interaction mode observed in both the docking and the model calculations involves the lactone ring.

Effective interfacial energy band engineering strategy toward high-performance triboelectric nanogenerator

Provided that electron transition ascribed to overlapping electron dominates the mechanism of contact electrification of triboelectric nanogenerators (TENGs), the electron transfer process occurs due to the built-up electric field between the triboelectrification surface and bottom electrode. In this work, we embed a solution-processed high-permittivity electron blocking layer (HPEBL) of LaZrO into the classical contact-separation mode TENG to build an energy barrier (ΔE > 1.3 eV) between ITO and PDMS, which could effectively block the transportation of electrons towards the bottom electrode. The surface potential decline rate of PDMS is obviously suppressed, extending the half-charge decay time by ∼3.1 times. A La0.1Zr0.9Ox HPEBL based TENG (H-TENG) demonstrates the electrical outputs with 215 V, 96.3 mA m−2 and 243.3 μC/m−2. Under the external load of 100 MΩ, the average gravimetric/volumetric power density and energy conversion efficiency can be calculated to be 59.34 μW g−1, 152.5 μW cm−3 and 39.2%, respectively. Furthermore, the dielectric behaviors of LaZrO thin films are investigated by metal–insulator-metal (MIM) devices. The Poole-Frenkel (PF) emission is found to dominate the leakage mechanism of LaZrO during operation. Consequently, increasing the relative permittivity and reducing the trap density could be indicated as the optimization orientation of HPEBL.

Increasing the kinetic stability of a gas‐phase contact ion‐pair through enhancement of the carbocation stability

AbstractThe occurrence of a hydrogen‐bonded contact ion pair (HBCIP, in the gas phase) between the dibenzotropylium cation and chloride has been suggested previously. However, the low barrier (ΔE‡, of ~1 kcal/mol) to its covalent counterpart can preclude its detection. In this work it is shown (through density functional theory calculations) that ΔE‡ can be increased significantly, based on larger but similar carbocations containing more benzene rings. Using the electrostatic potential as a measure of carbocation stability, along with its linear correlation with ΔE‡, one obtains a ΔE‡ value as high as ~3.7 kcal/mol for the HBCIP between the heptabenzotropylium cation and chloride. The trend for ΔE‡ can be explained by the deformation energy of the carbocation, from its structure in the HBCIP to that in the transition state.

Does mesoscopic elasticity control viscous slowing down in glassforming liquids?

The dramatic slowing down of relaxation dynamics of liquids approaching the glass transition remains a highly debated problem, where the crux of the puzzle resides in the elusive increase in the activation barrier ΔE(T) with decreasing temperature T. A class of theoretical frameworks-known as elastic models-attribute this temperature dependence to the variations of the liquid's macroscopic elasticity, quantified by the high-frequency shear modulus G∞(T). While elastic models find some support in a number of experimental studies, these models do not take into account the spatial structures, length scales, and heterogeneity associated with structural relaxation in supercooled liquids. Here, we propose and test the possibility that viscous slowing down is controlled by a mesoscopic elastic stiffness κ(T), defined as the characteristic stiffness of response fields to local dipole forces in the liquid's underlying inherent structures. First, we show that κ(T)-which is intimately related to the energy and length scales characterizing quasilocalized, nonphononic excitations in glasses-increases more strongly with decreasing T than the macroscopic inherent structure shear modulus G(T) [the glass counterpart of liquids' G∞(T)] in several computer liquids. Second, we show that the simple relation ΔE(T) ∝ κ(T) holds remarkably well for some computer liquids, suggesting a direct connection between the liquid's underlying mesoscopic elasticity and enthalpic energy barriers. On the other hand, we show that for other computer liquids, the above relation fails. Finally, we provide strong evidence that what distinguishes computer liquids in which the ΔE(T) ∝ κ(T) relation holds from those in which it does not is that the latter feature highly fragmented/granular potential energy landscapes, where many sub-basins separated by low activation barriers exist. Under such conditions, it appears that the sub-basins do not properly represent the landscape properties relevant for structural relaxation.

Cu-Ag nanocomposites in-situ formed on the surface of CuZr-based metallic glasses as highly efficient catalysts for improving catalytic behavior and reusability towards wastewater treatment

Minor element addition will be considered to modulate the atomic structures of materials to achieve surface activation for enhancing catalytic capability. Herein, Ag minor alloying enhances the catalytic behaviors of Cu-Zr-Al MGs in degrading dye molecules due to in situ formed Cu-Ag nanocomposites as highly efficient and stable catalysts. The higher degradation efficiency and faster reaction rate for Cu46Zr44.5Al7.5Ag2 ribbons than those of Cu47.5Zr46Al6.5 ribbons are accurately achieved more than 99% efficiency and 0.32 min−1 reaction rate within 20 min after 30th run. The thermal activation energy barrier (ΔE) of 5.97 kJ mol−1 for Cu46Zr44.5Al7.5Ag2 ribbons is lower than that of 8.47 kJ mol−1 for Cu47.5Zr46Al6.5 ribbons. The enhanced capability can be attributed to the corrosion engineering and electrochemical principle, the inclusion of Ag as a cathode contributes to forming a micro-electric couple with Cu as an anode to generate a variety of active copper-based nanocomposites due to surface modification. More importantly, introducing Ag atom can promote the enrichment of Cu-Ag nanocomplexes on the surface of ribbons in order to provide stronger surface activity and faster electron transfer to further improve catalytic performance. These findings are expected to help open up new functional applications of CuZr-based MGs in environment field.

Water-Stable Zero-Dimensional (C4H9)4NCuCl2 Single Crystal with Highly Efficient Broadband Green Emission.

Here, we report (C4H9)4NCuCl2 single crystals with a luminous intensity that remains largely the same after soaking in water for 24 h. (CH9)4NCuCl2 has a new type zero-dimensional framework, in which the isolated [CuCl2]- anions are wrapped by organic (C4H9)4N+ cations. As expected, (C4H9)4NCuCl2 shows a broad emission band at 508 nm with a photoluminescence quantum yield of approximately 82% at room temperature, stemming from self-trapped exciton (STE) emission. Temperature-dependent photoluminescence measurement reveals that there is an energy barrier ΔE (24.0 meV) between the intrinsic state and STE state, which leads to the increase in emission intensity with an increase in temperature (98-278 K), while the emission intensity begins to decrease when the temperature is higher than 278 K due to the effects of both thermal quenching and carrier scattering. Our findings provide a new idea for the design of lead-free anti-water stability metal halide materials.

Circumambulatory Rearrangements of 5-Halo-1,2,3,4,5-pentaphenylcyclopentadienes

DFT quantum chemical calculations at the CAM-B3LYP/Def2TZVP level of theory showed that intramolecular migrations of halogens in 5-halo-1,2,3,4,5-pentaphenylcyclopentadienes (C5Ph5Hlg, Hlg = F, Cl, Br, I) involve chiral conformation of their molecules with a propeller arrangement of phenyl groups via 1,5-sigmatropic shifts around the five-membered ring through asymmetric transition states with energy barriers ΔE≠ZPE of 42.5 (F), 26.2 (Cl), 20.2 (Br), and 15.2 kcal/mol (I). The results were consistent with the data of dynamic NMR spectroscopy. The P and M enantiomers are readily interconvertible (ΔE≠ZPE = 1.7–3.7 kcal/mol) by way of synchronous flips of the phenyl groups. The calculated barriers to alternative 1,3-halogen shifts in C5Ph5Hlg are considerably higher than those for 1,5-shifts: ΔE≠ZPE = 60.7 (F), 38.6 (Cl), 32.0 (Br), and 27.9 kcal/mol (I).

Optimal potential well for maximizing performance of bi-stable energy harvester

This letter provides an investigation on the combined influence of the potential barrier (ΔE) and separation gap of a double well (Δx) to maximize the performance of an electromagnetic bistable energy harvester (BEH). A concise method based on a high-fidelity orthogonal array sampling technique is further developed to facilitate the searching of the parameter-set corresponding to the desired potential well. According to numerical and experimental results, a barrier depth slightly lower than the threshold of interwell oscillation cooperating with a properly large separation gap is preferred for improving the power output, and enlarging the redundancy of the excitation intensity for inducing the well escape behavior. Compared to the potential well with the same barrier depth but a narrow separation gap of 1.7 mm, the optimal well with a larger Δx of 2.3 mm not only demonstrates a 60% higher output power at an acceleration of 1 g, but the intensity threshold for interwell oscillation is also reduced to 0.7 g. This work presents an insight and a method into shaping the potential well for the optimized performance and increased redundancy of a bistable configuration.

Roles of Precursor Conformation and Adatoms in Ullmann Coupling: An Inverted Porphyrin on Cu(111)

Surface diffusion, molecular conformation, and on-surface coupling reactions are key processes for building tailored molecular nanostructures such as graphene nanoribbons, polycyclic aromatic hydrocarbons, and one-dimensional/two-dimensional (2D) polymers. Here, we study the surface diffusion and coupling in situ of a chlorinated porphyrin, namely 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin (Cl4TPP), using a combined scanning tunneling microscopy (STM), density functional theory (DFT), and X-ray photoelectron spectroscopy approach. Using STM, we obtain surface migration and rotation barriers ΔE of 0.77 ± 0.09 and 0.93 ± 0.28 eV, respectively, indicative of covalent binding to the surface. In fact, we find that the precursors as well as all the reaction species exclusively (≈100%) adopt a peculiar “inverted” conformation covalently bonded to Cu(111). Using DFT, we have mapped two coupling reaction pathways: direct dechlorination and Cu adatom-mediated Ullmann coupling. We find that the latter is essential...

Non-Isothermal Crystallisation Kinetics of Carbon Black- Graphene-Based Multimodal-Polyethylene Nanocomposites.

The effect of carbon black (CB) and microwave-induced plasma graphene (g) on the crystallisation kinetics of the multimodal high-density polyethylene was studied under non-isothermal conditions. The non-isothermal crystallisation behaviour of the multimodal-high-density polyethylene (HDPE), containing up to 5 wt.% graphene, was compared with that of neat multimodal-HDPE and its carbon black based nanocomposites. The results suggested that the non-isothermal crystallisation behaviour of polyethylene (PE)-g nanocomposites relied significantly on both the graphene content and the cooling rate. The addition of graphene caused a change in the mechanism of the nucleation and the crystal growth of the multimodal-HDPE, while carbon black was shown to have little effect. Combined Avrami and Ozawa equations were shown to be effective in describing the non-isothermal crystallisation behaviour of the neat multimodal-HDPE and its nanocomposites. The mean activation energy barrier (ΔE), required for the transportation of the molecular chains from the melt state to the growing crystal surface, gradually diminished as the graphene content increased, which is attributable to the nucleating agent effect of graphene platelets. On the contrary, the synergistic effect resulting from the PE-CB nanocomposite decreased the ΔE of the neat multimodal-HDPE significantly at the lowest carbon black content.

First-principles study of the formation of glycine-producing radicals from common interstellar species

Glycine, the simplest amino acid, has been intensively searched for in molecular clouds, and the comprehensive clarification of the formation path of interstellar glycine is now imperative. Among all the possible glycine formation pathways, we focused on the radical pathways revealed by Garrod (2013). In the present study, we have precisely investigated all the chemical reaction steps related to the glycine formation processes based on state-of-the-art density functional theory (DFT) calculations. We found that two reaction pathways require small activation barriers (ΔE‡ ≤ 7.75 kJ mol–1), which demonstrates the possibility of glycine formation even at low temperatures in interstellar space if the radical species are generated. The origin of carbon and nitrogen in the glycine backbone and their combination patterns are further discussed in relation to the formation mechanisms. According to the clarification of the atomic correspondence between glycine and its potential parental molecules, it is shown that the nitrogen and two carbons in the glycine can originate in three common interstellar molecules, methanol, hydrogen cyanide, and ammonia, and that the source molecules of glycine can be described by any of their combinations. The glycine formation processes can be categorized into six patterns. Finally, we discussed two other glycine formation pathways expected from the present DFT calculation results.

Investigation on the crystallization behavior and morphology of β-nucleated isotactic polypropylene/glass fiber composites

ABSTRACTThe isotactic polypropylene (iPP) with different uniformities of stereo-defect distribution was synthesized, and the β-nucleated iPP/glass fiber composites (TPPA-GF and TPPB-GF) were prepared. The influence of glass fiber on the non-isothermal crystallization kinetics, β-phase crystallization, and morphology behavior of the composites were investigated by means of differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), and wide angle X-ray diffraction (WAXD). The results revealed that for both TPPA-GF and TPPB-GF, as the amount of GF increases, the crystallization peak temperature and relative degree of crystallinity increase gradually, while crystallization peak width decreases gradually. Meanwhile, the half crystallization time t1/2 of both TPPA and TPPB decreases gradually, indicating that the addition of GF can accelerate the crystallization of both TPP-A and TPP-B. Moreover, the addition of glass fiber decreases the energy barriers ΔE and makes the composites to crystallize easier. The results of melting behavior study and WAXD indicate that high cooling rate leads to relatively low crystallization temperature and low thermal stability, resulting in higher β-phase content with relatively low thermal stability, while low cooling rate leads to high crystallization temperature and high thermal stability, which is more favorable for the formation of less amount of β-phase with high thermal stability. For both TPPA and TPPB, the higher the content of glass fiber, the lower the βc. The addition of glass fiber not only reduces the content of β-phase but also destroys its spherulite morphology. It was also observed that the glass fiber is more uniformly dispersed in TPPB compared with TPPA.

Sulfonation mechanism of benzene with SO3 in sulfuric acid or oleum or aprotic solvent: Obeying the transition state theory via a trimolecular electrophilic substitution clarified by density functional theory calculation

It is found that the benzene sulfonation in sulfuric acid is a brief two-step reaction by DFT calculation at the B3lyp/6-311++G(d,p) level. First, a H2SO4 molecule generates a SO3 and a H2O molecule through a hydroxyl-oxygen protonation completed by another H2SO4 molecule. The protonation requires to cross a barrier ΔE∗ of 10kcal/mol. Then, the SO3 molecule accomplishes the sulfonation through a trimolecular electrophilic substitution. The trimolecular system is C6H6+SO3+H2SO4. The H2SO4 is a catalyst; it is not only a proton acceptor, but also a donor. In aprotic solvents the trimolecular system is C6H6+2SO3, but in liquid SO2 the system is C6H6+SO3+SO2. The trimolecular sulfonations all follow the transition state theory. SO3 is the electrophile. The three molecules first form spontaneously a trimolecular π-complex, and then across a transition state (TS) and complete the sulfonation. The calculation shows that in addition to SO2 as solvent, in other polar solvents the barriers are 1–5kcal/mol, thus the sulfonations are actually a spontaneous reaction. These calculation results are in agreement with the kinetic and experimental results. Based on this study, the popular benzene sulfonation mechanism in textbooks needs to be corrected.