Computational study of singlet and triplet sulfonylnitrenes insertion into the C―C or C―H bonds of ethylene

Formation of N‐sulfonylaziridines, N‐ethylidenesulfonamides, N‐vinylsulfonamides and 4,5‐dihydro‐1,2,3‐oxathiazole 2‐oxides by the reaction of singlet and triplet trifluoromethyl‐, methyl‐ and tosylnitrenes with ethylene is studied computationally at the B3LYP/6‐311++G(d,p) level of theory in both gas phase and in solution. Singlet sulfonylnitrenes react with ethylene via [1 + 2]‐cycloaddition exothermically to give N‐sulfonylaziridines. Triplet sulfonylnitrenes are formed from the singlet ones by the intersystem crossing with the energy barrier not exceeding 2.5 kcal/mol and react in a stepwise fashion by C‐addition or H‐abstraction. The C‐addition gives rise to the formation of N‐sulfonylaziridines or N‐ethylidenesulfonamides depending on the S―N―C_sp3―C_sp2 dihedral angle, with the barrier to rotation about the N―C_sp3 bond not exceeding 2.5 kcal/mol. The H‐abstraction results in N‐vinylsulfonamides. Transformation of N‐sulfonylaziridines to N‐ethylidenesulfonamides requires to overcome the barrier of 57–60 kcal/mol, N‐ethylidenesulfonamides to 4,5‐dihydro‐1,2,3‐oxathiazole 2‐oxides—74–80 kcal/mol and N‐vinylsulfonamides to N‐ethylidenesulfonamides—about 64 kcal/mol. The use of the polarizable continuum model does not lead to a change of the course of the reaction of trifluoromethanesulfonylnitrene with ethylene and only slightly affects the relative energies of the products, intermediates and transition states. Copyright © 2014 John Wiley & Sons, Ltd.     

A theoretical study on the reaction mechanism and kinetics of allyl alcohol (CH2 = CHCH2OH) with ozone (O3) in the atmosphere

Volatile organic compounds (VOCs) play a major role in the physical and chemical process of the tropospheric chemical reactions in both polluted and remote environments. A theoretical work has been presented on the VOC of allyl alcohol with O₃ molecule is investigated using density functional theory methods. The reaction profile is initiated through the cycloaddition of ozone which leads to the formation of primary ozonide with minimal relative energy barrier of 1.31 kcal/mol which decomposes to form carbonyl molecule and carbonyl oxide. Carbonyl oxide, i.e. criegee intermediates reacts with various atmospheric species to produce more hazardous and toxic end products to the environment. The condensed form of Fukui function was calculated to predict reactive sites of the primary and secondary reaction profile. The rate coefficient using CVT with SCT over the temperature range of 258–358K is analysed and also to study the atmospheric effects of allyl alcohol in the atmosphere. The predicted rate coefficient for the favourable reaction pathway of k_p1 found to be 1.190 ×10^?15 cm³/molecule/sec and comparable with the experimental result at 298 K. The atmospheric lifetime of allyl alcohol was found to be around 10 hours in addition to that global warming potentials are compared with the CO₂.     

Organocatalysis: quantum chemical modeling of nucleophilic addition to α,β‐unsaturated carbonyl compounds

One of the successful transformations within the field of organocatalysis, the organocatalytic asymmetric addition of nitromethane to α,β‐unsaturated aldehydes and ketones, has been studied by quantum chemical modeling. The level of accuracy of the hybrid density functional theory method B3LYP/6‐31G(d) was compared to a high level ab initio benchmark for this reaction. It is concluded that B3LYP/6‐31G(d) performs very well for this reaction type, giving good estimates of critical energies. The reaction between acrolein and nitromethane was studied in detail. The reaction mechanism revealed an intermediate oxazolidin structure, which is currently unknown. Alkyl substitution in various positions on the amine catalyst or α,β‐unsaturated carbonyl compound influences the reactivity in a predictive fashion. The iminium ion, prop‐2‐en‐iminium, is less activated towards nucleophilic attack compared to protonated acrolein. Copyright © 2007 John Wiley & Sons, Ltd.     

Enantio‐differentiating reactions of a racemic γ‐lactone enolate with chiral esters. A DFT investigation

The acylation of lithium (±)‐spiro‐γ‐lactone enolate 5 by the O‐protected methyl (?)‐(S)‐lactate or the O‐protected methyl (+)‐(S)‐mandelate occurs through enantio‐differentiating reactions. The (S,S)‐enolate 5 is the most reactive with the lactate whereas the (R,R)‐enolate 5 selectively reacts with the mandelate. According to theoretical calculations at the B3LYP/6‐31G(++)(d,p) level of theory of 40 intermediates of this Claisen condensation, the experimental results are compatible with a previous chelation of the ester by an auxiliary cation lithium arising from the medium. The addition reaction occurs through a chelation process mediated by the counterion of the enolate. More stable tetrahedral intermediates including two lithium cations result from an antiperiplanar transition state. These results clearly demonstrate that the presence of a second lithium cation (the first lithium cation is solvated by di‐isopropylamine and the second one is solvated by a THF molecule or a di‐isopropylamide anion) stabilizes the tetrahedral intermediate and is compatible with an antiperiplanar transition state according to the Felkin–Anh model. Copyright © 2010 John Wiley & Sons, Ltd.     

NH_3与MgH_2反应机理的密度泛函理论研究

采用密度泛函理论B3LYP方法研究了NH_3与MgH_2的放氢反应机理,在6-311G(d,p)基组水平上对反应物、中间体、过渡态及产物进行了全几何参数优化.频率分析和内禀反应坐标(IRC)计算证实了中间体和过渡态的正确性和相互连接关系.计算结果表明:反应分两步单通道的氢取代过程,且反应过程相类似,反应生成Mg(NH_2)_2和2H_2.两步氢取代反应所释放的H_2中两个H原子分别来源于NH_3和MgH_2.反应脱氢的关键在于克服N—H键断裂所需能量.     

NH3与MgH2反应机理的密度泛函理论研究

采用密度泛函理论B3LYP方法研究了NH3与MgH2的放氢反应机理,在6-311G(d, p)基组水平上对反应物、中间体、过渡态及产物进行了全几何参数优化。频率分析和内禀反应坐标(IRC)计算证实了中间体和过渡态的正确性和相互连接关系。计算结果表明。反应分两步单通道的氢取代过程,且反应过程相类似,反应生成Mg(NH2)2和2H2。两步氢取代反应所释放的H2中两个H原子分别来源于NH3和MgH2。反应脱氢的关键在于克服N—H键断裂所需能量。     

环戊二烯与二氢呋喃类化合物Diels-Alder反应的理论研究

采用量子化学密度泛函理论(DFT)在B3LYP/6-311++G **水平上对环戊二烯与2(5H)-呋喃酮、丁烯二酸酐和2,5-二氢呋喃的Diels-Alder反应机理进行了理论研究,并且考虑了溶剂化效应和取代基效应对反应机理及能垒的影响。结果表明,本文所涉及的环戊二烯与二氢呋喃类化合物的Diels-Alder加成反应是以协同方式进行的;羰基取代基的吸电子作用是造成产物中C(1)-C(2)、C(3)-C(4)键键长增加的主要原因;反应所涉及到的FMO相互作用主要是环戊二烯的HOMO与二氢呋喃类化合物的LUMO之间的相互作用,羰基对反应活化能的影响主要是通过降低呋喃类化合物的LUMO能级,减小与环戊二烯的HOMO的能级差异,从而有利于反应进行的;反应2的活化能垒最低,从动力学的角度考虑在室温下可以进行。     

环戊二烯与二氢呋喃类化合物Diels-Alder反应的理论研究

采用量子化学密度泛函理论(DFT)在B3LYP/6-311++G **水平上对环戊二烯与2(5H)-呋喃酮、丁烯二酸酐和2,5-二氢呋喃的Diels-Alder反应机理进行了理论研究,并且考虑了溶剂化效应和取代基效应对反应机理及能垒的影响。结果表明,本文所涉及的环戊二烯与二氢呋喃类化合物的Diels-Alder加成反应是以协同方式进行的;羰基取代基的吸电子作用是造成产物中C(1)-C(2)、C(3)-C(4)键键长增加的主要原因;反应所涉及到的FMO相互作用主要是环戊二烯的HOMO与二氢呋喃类化合物的LUMO之间的相互作用,羰基对反应活化能的影响主要是通过降低呋喃类化合物的LUMO能级,减小与环戊二烯的HOMO的能级差异,从而有利于反应进行的;反应2的活化能垒最低,从动力学的角度考虑在室温下可以进行。     

H_2CO+OH~-反应的理论研究(英文)

用量化从头算方法在MP4(SDTQ)理论水平上首次考察了甲醛和氢氧根负离子反应的所有可能的反应通道.用6-311 G(3df,3pd)基组对所有的反应中间体、过渡态和产物开展了结构优化和单点能量计算,并经频率分析和内禀反应反应坐标计算(IRC)确认反应物、中间体、过渡态和产物的相关性.在H2CO OH-所有可能的反应通道中生成CHOO- H2的通道是该反应的最可几通道,而由于羰基的存在生成H3O-的通道更容易分解产生CHOO- H2.在高计算水平下计算的氢交换反应结果与文献报道相同.通过计算提出亲核加成过程的反应通道,主要产物生成H2和生成COOH-/HCOO-/OCHO-异构体.所有反应通道的反应几率顺序为COOH- H2>H3O- CO>HCHO OH->CHO- H2O>HCOO- H2>OCHO- H2.     

NH3与MH(M=Li,Na)反应机理的密度泛函理论研究

采用密度泛函理论B3LYP方法研究了NH3与MH(M=Li,Na)的放氢反应机理,在6-311G(2d,2p)基组水平上对反应物、中间体、过渡态及产物进行了全几何参数优化,频率分析和内禀反应坐标(IRC)计算证实了中间体和过渡态的正确性和相互连接关系。计算结果表明,NH3与MH(M=Li,Na)的反应均为单通道的氢取代反应,反应生成LiNH2(NaNH2)与H2。     

NH3与MH（M=Li,Na）反应机理的密度泛函理论研究

采用密度泛函理论B3LYP方法研究了NH₃与MH（M=Li,Na）的放氢反应机理.在6-311G（2d.2p）基组水平上对反应物、中间体、过渡态及产物进行了全几何参数优化.频率分析和内禀反应坐标（IRC）计算证实了中间体和过渡态的正确性和相互连接关系.计算结果表明,NH₂与MH（M=Li,Na）的反应均为单通道的氢取代反应,反应生成LiNH₂（NaNH₂）与H₂.     

A theoretical density functional study of association of Zn2+ with oxazolidine and its thio derivatives in the gas phase

We have performed density functional theory (DFT) calculations in order to study the gas‐phase interaction of oxo‐ and thio‐oxazolidine derivatives with Zn²⁺. The calculations were performed at B3LYP/6‐311+(2df,2p) level of theory. It has been found, in all cases, that the direct association of Zn²⁺ with the carbonyl and thiocarbonyl groups takes place at the heteroatom attached to position 2 irrespective of its nature. This preference has been attributed to the resonance effects caused by the nearest heteroatoms (oxygen and nitrogen). The most stable complexes correspond to structures with Zn²⁺ bridging between the heteroatom at position 2 or 4 of the 4‐ or 2‐enol (or the 4‐ or 2‐enethiol) tautomer and the dehydrogenated ring nitrogen atom, N3. Zn²⁺ association has a clear catalytic effect on the tautomerization processes which connect the oxo–thione forms with the enol–enethiol tautomers. Hence, although the enol–enethiol tautomers of oxazolidine and its thio derivatives should not be observed in the gas phase, the corresponding Zn²⁺ complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Zn²⁺ binding energies. Copyright © 2010 John Wiley & Sons, Ltd.     

NH_3与CaH_2反应机理的密度泛函理论研究

基于密度泛函理论(DFT)当中的B3LYP(杂化密度泛函)方法,于6-311G(d,p)基组水平上对NH_3与CaH_2的反应机理进行了计算分析,对反应过程中的反应物、中间体、过渡态及产物进行了全几何参数优化,得到其构型和基本参数.对得到的中间体和过渡态进行频率分析和内禀反应坐标(IRC)计算,以证实中间体和过渡态的正确性和相互连接关系.使用QCISD方法在6-311G(d,p)基组水平对各驻点的单点能进行计算,给出能量信息.计算结果表明:CaH_2与NH_3主要以摩尔比为1:2进行反应,分两步氢取代过程,生成产物Ca(NH2)2和2H2.反应所释放的H2中两个H原子分别来源于CaH_2和NH_3,反应的关键是脱氢,主要在于克服N—H键断裂所需能量.相比较而言从NH_3中脱氢比从—NH2中脱氢较易.     

CX2+CH2O (X=F, Cl, Br)环加成反应的密度泛函理论计算

用密度泛函理论,在B3LYP/6-311 G(d)水平上研究了CX2 CH2O(X=F,Cl,Br)环加成反应一条三过渡态三中间体路径的反应机理,全参数优化了反应势能面各驻点的几何构型,用内禀反应坐标(IRC)和频率分析方法,对过渡态进行了验证.用高级电子相关校正的耦合簇[CCSD(T)/6-311 G(d)]方法对优化构型进行了单点能计算.采用经Wigner校正的Eyring过渡态理论和热力学方法,研究了该反应通道的热力学及动力学性质.从热力学和动力角度综合分析,该途径CF2与GH2O的环加成反应难以发生,而CCl2及CBr2与CH2O反应的适宜温度范围均为400～1000K,如此,反应既具有较大的自发趋势和平衡常数,又具有较快的反应速率.     

Copper(I)‐catalyzed reaction of unsymmetrical alkyne with HB(pin): a density functional theory study

With the aid of density functional theory calculations, we have investigated the mechanism of copper(I)‐catalyzed reaction between unsymmetrical alkyne 1‐phenyl‐1‐butyne and HB(pin). The results of the density functional theory calculations show that the reaction mechanism involves syn‐addition of catalyst ([NHC]CuH) (NHC = N‐heterocyclic carbene) to 1‐phenyl‐1‐butyne to form the alkenyl copper intermediates 2a and 5a , and then intermediates 2a and 5a react with HB(pin) to give intermediates 3 ( 3a , 3b ) and 6 ( 6a , 6b ), and finally elimination of catalyst completes the catalytic cycle and yields the α‐product P₁ and β‐product P₂ . We found that α‐product should be more favored than β‐product. The calculated results are consistent with the experimental findings. The present paper may provide a useful guide for understanding other analogous copper‐catalyzed hydroboration of unsymmetrical alkynes.     

A quantum chemical study on the OH radical quenching by natural antioxidant fisetin

In this work, the antioxidant ability of fisetin was explored toward hydroxyl (?OH) radical in aqueous and lipid solution using density functional level of theory. Different reaction mechanisms have been studied: hydrogen atom transfer, single electron transfer followed by proton transfer, and radical adduct formation, and sequential proton loss electron transfer. Rate constants for all possible reaction sites have been calculated using conventional transition state theory in conjunction with the Collins‐Kimball theory. Branching ratios for the different channels of reaction are reported for the first time. Results show that the reactivity of fisetin toward hydroxyl (^?OH) radical takes place almost exclusively by radical adduct formation regardless of the polarity of the environment. Also, the single‐electron transfer process seems to be thermodynamically unfavorable in both media.     

A spectroscopic study of the adsorption and reactions of methanol,formaldehyde and methyl formate on clean and oxygenated Cu(110) surfaces

The adsorption and reaction of methanoi (CH₃OH), methyl formate (CH₃OCHO) and formaldehyde (H₂CO) on clean and oxygen-covered Cu(110) surfaces has been studied with EELS, UPS and thermal desorption spectroscopy (TDS). The clean surface is relatively unreactive but adsorbed oxygen readily attacks the hydroxyl proton and formyl carbon atoms to generate the intermediate methoxy (CH₃O) and formate (HCOO). Methyl formate is split into two intermediates, methoxy and formate. By correlating the three techniques we analyse (a) the condensed multilayer at 90 K; (b) the weakly bound molecular monolayer states prior to dissociation or reaction and (c) the reactive intermediates at higher temperatures. Formaldehyde forms the surface polymer polyoxymethylene [(CH₂O)_n] in the monolayer on Cu(110) which subsequently reacts with oxygen to generate formate. No molecular formaldehyde was observed above 120 K. Correlation of the EELS and UPS results for polyoxymethylene shows that an earlier interpretation by Rubloff et al. [Phys. Rev. B14 (1976) 1450] of anomalous shifts in the formaldehyde UPS spectrum on surfaces is incorrect, and due simply to the new polymeric structure of surface formaldehyde. Methyl formate coordinates to copper via the carbonyl lone pair orbital and methanol via the oxygen lone pair orbital. No evidence was found for methyl formate synthesis by dimerization of formaldehyde (the Tischenko reaction) or dehydrogenation of methanol on the clean Cu(110) surface. These latter reactions are facile over copper catalysts at atmospheric pressure. The success of the oxidation experiments and the failure of the synthesis reactions in UHV is a consequence of the pressure dependence of the equilibrium constants for the different reactions. As found previously in Fischer-Tropsch studies, condensation reaction equilibria are pressure dependent and product formation is considerably suppressed at UHV pressures.     

Mechanism for the reactions of sulfides and sulfoxides with hypochlorites: racemization and oxygen exchange of oxysulfonium salts and sulfoxides

Density functional theory computations have been performed on the oxidations of sulfides and sulfoxides with hypochlorite ion (OCl^?), hypochlorous acid, and alkyl hypochlorites to study the mechanism of the reactions. The OCl^? anion transforms sulfides to sulfoxides and sulfoxides to sulfones in oxygen transfers. The oxygen atom of QOCl hypochlorites (Q = H, Me, t‐Bu) attacks at the sulfur atom of the substrates, and oxysulfonium cation intermediates are formed; the departure of the leaving Cl^? is catalyzed by soft Lewis acids. The structures of the early transition states are determined by highest occupied molecular orbital–lowest unoccupied molecular orbital interactions. The sulfur compounds are the electron acceptors in the reaction with OCl^?, but they are the electron donors in the reactions with QOCl. The attack of Cl^? at the oxygen atom of oxysulfonium cation intermediates leads to the sulfide and QOCl precursors and can result in racemization, oxygen exchange, and reduction of oxysulfonium salts in reversible reactions. The attack of Cl^? at the sulfur atom of oxysulfonium salts produces λ⁴‐sulfane intermediates. Oxysulfonium cations can be transformed into sulfoxide products with the attack of Cl^? or water at the α‐carbon atom of the O‐alkyl group. The attack of water at the sulfur atom of oxysulfonium cation leads to hydrolysis or oxygen exchange reactions. Racemization and oxygen exchange of sulfoxides proceeds in similar reactions, through the formation of hydroxysulfonium cation intermediates in acidic media in the presence of Cl^?. Chlorosulfonium cations are of very high energy; their intermediacy can be ruled out in the reactions of sulfides with hypochlorites. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanistic study on Mo(CO)6‐catalyzed intramolecular [2 + 2] or [2 + 2 + 1] cycloaddition reaction of 5‐allenyl‐1‐ynes

By means of density functional theory, the Mo(CO)₆‐catalyzed intramolecular [2 + 2] or [2 + 2 + 1] cycloaddition reaction of 5‐allenyl‐1‐ynes was investigated. All the intermediates and transition states were optimized completely at B3LYP/6‐311++G(d,p) level (LANL2DZ(f) for Mo). Calculations indicate that the complexation of 5‐allenyl‐1‐ynes with Mo(CO)₆ occurred preferentially at the triple bond to give the complex M1 and then the complexation with the distal double bond of the allenes generates the complex M5 . In this reaction, Mo(CO)₆‐catalyzed intramolecular [2 + 2] cycloaddition is more favorable than [2 + 2 + 1] cycloaddition. The reaction pathway Mo(CO)₆ + R → M5 → T7 → M12 → M13 → T11 → M18 → P4 is the most favorable one, and the most dominant product predicted theoretically is P4 . The solvation effect is remarkable, and it decreases the reaction energy barriers. Copyright © 2011 John Wiley & Sons, Ltd.     

吡喃木糖热裂解机理的密度泛函理论研究

采用密度泛函理论理论方法 M062X/6-311++G(d,p),对吡喃木糖的热解反应机理进行了理论计算分析.针对吡喃木糖热解可能发生的化学反应共设计了九条可能的热解路径,并对各路径中的反应物、中间体和过渡态的几何结构进行了能量梯度全优化,并在梯度全优化的基础上计算了各热解反应路径的热力学和动力学参数.文中以两大类方式来设计反应路径:1)木糖首先经过过渡态TS1发生开环反应生成链状中间体2,该步的反应能垒为188.7 kJ/mol,对于中间体2共设计了五种可能的热解反应路径;2)考虑双键同时断裂的情况,木糖先发生脱水反应,接着按C-C和C-O键同时断裂的情况发生开环反应,针于这种情况共设计了四条可能的热解路径.计算结果表明,吡喃木糖热解的主要反应产物有乙醇、乙醛、糠醛、丙酮、酸类、CO_2和CO等小分子化合物.