Xiaojun Tan

Theoretical studies on the alkylidene germylenoid H2C=GeLiF and its insertion reaction with R-H (R = F, OH, NH2, CH3)

The geometries and isomerization of the alkylidene germylenoid H2C=GeLiF as well as its insertion reactions with R-H (R = F, OH, NH2, CH3) have been systematically investigated at the B3LYP/6-311+ G* level of theory. The potential barriers of the four insertion reactions are 110.6, 145.0, 179.4, and 250.6 kJ/mol, respectively. Here, all the mechanisms of the four reactions are identical to each other, i.e., an intermediate has been formed first during the insertion reaction. Then, the intermediate could dissociate into the substituted germylene (H2C=GeHR) and LiF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies for the four reactions are 43.6, 78.8, 113.5, and 128.0 kJ/mol, respectively. Compared with the insertion reaction of H2C= Ge∶ and R-H, the introduction of LiF makes the insertion reaction occur more difficultly. Furthermore, the effects of halogen (F, Cl, Br) substitution and inorganic salts employed on the reaction activity have also been discussed. As a result, the relative reactivity among the four insertion reactions should be as follows: H-F > H-OH > H-NH2 > H-CH3.

A computational study of the addition reaction of cyclopropenylidene with methyleneimine

The reaction mechanism between cyclopropenylidene and methyleneimine has been systematically investigated at the MP2/6–31+G* level of theory, including geometry optimization, vibrational analysis, and energy property for the involved stationary points on the potential energy surface. The energies of the different species are calculated by the single point energy calculations of CCSD(T)/6-31+G*//MP2/6-31+G* level. It was found that an important initial intermediate (INTA) characterized by spiro-compound structure has been located along the three pathways (1), (2R), and (2L) firstly. After that, another common intermediate (INTB) has been formed via TSB. At last, three different products possessing three- and four-membered ring characters have been obtained through corresponding reaction pathways. In the first reaction pathway (1), a three-membered ring alkyne compound has been obtained. As for the other two reaction pathways (2R) and (2L), the four-membered ring conjugated diene compound has been produced. As a result, the energy barrier of the rate-determining step of the pathway (1) is lower than that of the pathway (2R) and (2L), and the ultima product of pathway (2R) and (2L) is more stable than that of the pathway (1).

Theoretical insights into the cycloaddition reaction mechanism between ketenimine and methyleneimine: An alternative approach to the formation of pyrazole and imidazole

AbstractThe cycloaddition reaction mechanism between interstellar molecules, ketenimine and methyleneimine, has been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method in order to better understand the reactivity of nitrogenous cumulene ketenimine with the C =N double bond compound methyleneimine. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. Calculations show that five-membered cyclic carbene intermediates could be produced through pericyclic reaction processes between ketenimine and methyleneimine. Through the subsequent hydrogen transfer processes, carbene intermediates can be isomerized to the pyrazole and imidazole compounds, respectively. The present study is helpful to understand the formation of prebiotic species in interstellar space. Graphical AbstractThe cycloaddition reaction mechanism between interstellar molecules, ketenimine and methyleneimine, has been systematically investigated theoretically. The products of this reaction are pyrazole and imidazole compounds, respectively.

Theoretical study on the reaction mechanism of azacyclopropenylidene with azetidine: an insertion process

The mechanism of reaction between azacyclopropenylidene and azetidine has been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method to better understand the azacyclopropenylidene reactivity with azetidine four-membered cycle. Geometry optimization, vibrational analysis, and energy properties for the involved stationary points on the potential energy surface have been calculated. It was found that at the first step of this reaction, azacyclopropenylidene can insert into azetidine cycle at its C-N or C-C bond to form spiro intermediate IM. It was found that azacyclopropenylidene insertion into C-N bond is easier than into C-C bond. Through the ring-opening step at C-C bond of azacyclopropenylidene fragment, IM can transfer to product P1, which is named as pathway (1). On the other hand, through the H-transferred step and subsequent ring-opened step at C-N bond of azacyclopropenylidene fragment, IM can turn into product P2, which is named as pathway (2). From the thermodynamics viewpoint, P2 allene is the dominating product. From the kinetic viewpoint, the pathway (1) of formation to P1 is primary.

Theoretical study on the reaction mechanisms between propadienylidene and R-H (R=F, OH, NH2, CH3): an alternative approach to the formation of alkyne

The reaction mechanisms between propadienylidene and R–H (R=F, OH, NH2, CH3) have been systematically investigated employing the second-order Moller–Plesset perturbation theory (MP2) method in order to better understand the reactivity of propadienylidene with those R–H compounds. We have investigated the reaction mechanisms and obtained the possible potential energy surface of these reactions, and we found the mechanisms of four reactions are identical to each other. Based on the calculated results, we can see that there are three steps along the reaction pathway of propadienylidene and R–H. The first step is that propadienylidene inserts into R–H bond to form an allene compound. The second- and third-steps are relevant to the H-transfer reaction, and the final product is alkyne.

DFT STUDY ON THE MECHANISM OF THE ADDITION REACTION BETWEEN CARBENE AND GLYCINE

The mechanism of addition reaction between the singlet carbene and glycine has been investigated at the B3LYP/6-311+G* level of theory, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Computational results suggest that there are two reaction pathways (1) and (2) during the addition process. In the pathway (1), carbene attacks the C=O bond from the H1C1C2 side of glycine to form an intermediate (IM1), which is a barrier-free exothermic reaction. Then, IM1 isomerizes to a product (Pro1) via a transition state (TS1) with a potential barrier of 25.7 kJ/mol. Similarly, in the pathway (2), carbene attacks the C=O bond from the H2C1C2 side of glycine to form an intermediate IM2. Subsequently, IM2 isomerizes to Pro2 via TS2, where the Pro2 and Pro1 are enantiomers actually. The calculated potential barrier of 51.3 kJ/mol is higher than that of the pathway (1). Correspondingly, the reaction energy for the both pathways is -258.5 kJ/mol. Additionally, the atoms in molecules (AIM) theory has also been performed to characterize the bonding interaction and structural features for the addition reaction.

Insights into the cycloaddition reaction mechanism between ketenimine and unsaturated hydrocarbon: A theoretical study

The cycloaddition reaction mechanisms between interstellar molecule ketenimine and unsaturated hydrocarbon (ethyne and ethylene) have been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. The calculated results show that it can be produced the five-membered cyclic carbene intermediates through pericyclic reaction processes between ketenimine and ethyne (or ethylene). For the reaction between ketenimine and ethyne, through the following H-transferred processes, carbene intermediate can be isomerized to the pyrrole compounds. For the reaction between ketenimine and ethylene, carbene intermediate can be isomerized to the pyrroline compounds. The present study is helpful to understand the reactivity of nitrogenous cumulene ketenimine and the formation of prebiotic species in interstellar space.

Theoretical study on the cycloaddition reaction mechanism between ketenimine and acetonitrile

The cycloaddition reaction mechanism between interstellar molecules ketenimine and acetonitrile has been sys- tematically investigated employing the second-order Moller-Plesset perturbation theory method in order to better understand the reactivity of heterocumulene ketenimine with acetonitrile. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. Calculations show that five-membered cyclic carbene intermediates could be afforded through pericyclic reaction processes between ketenimine and acetonitrile. Through the following intramolecular H-transfer processes, carbene intermediates can be isomerized to the corresponding 2-methylimidazole and 3-methylpyrazole derivatives, respectively. In addition, imidazole and pyrazole compounds can be produced through the intermolecular H-transfer processes on the basis of the formed cyclic carbene intermediates. The present study is helpful to understand the formation of prebiotic species in interstellar space.

Theoretical study on the cycloaddition reaction mechanism between ketenimine and hydrogen cyanide

The cycloaddition reaction mechanism between interstellar molecules ketenimine and HCN has been systematically investigated employing the second-order Moller-Plesset perturbation theory (MP2) method in order to better understand the reactivity of nitrogenous cumulene ketenimine with carbon-nitrogen triple bond compound HCN. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. The calculated results show that it can be produced the five-membered cyclic carbene intermediates through pericyclic reaction processes between ketenimine and HCN. Through the following H-transferred processes, carbene intermediates can isomerize to the pyrazole and imidazole compounds, respectively. The present study is helpful to understand the formation of prebiotic species in interstellar space.

INSIGHTS INTO THE REACTION MECHANISM BETWEEN AZACYCLOPROPENYLIDENE AND AZACYCLOPROPANE: A THEORETICAL STUDY

ABSTRACT The reaction mechanism between azacyclopropenylidene and azacyclopropane has been systematically investigated employing the second-order Moller-Plesset perturbation theory (MP2) method to better understand the azacyclopropenylidene reactivity with three-membered ring compound azacyclopropane. Geometry optimization, vibrational analysis, and energy property for the involved stationary points on the potential energy surface have been calculated. For the first step of this reaction, azacyclopropenylidene can insert into azacyclopropane at its C-N bond to form a spiro intermediate IM. Through the ring-opened step at C-C bond of azacyclopropenylidene fragment, IM can transfer to product P1, which is named as pathway (1). On the other hand, through the H-transferred step and subsequent ring-opened step at C-N bond of azacyclopropenylidene fragment, IM can turn into product P2, which is named as pathway (2). From the thermodynamics viewpoint, the P2 is the dominating product. From the kinetic viewpoint, the pathway (1) of formation to P1 is primary.