Dacheng Feng

The cooperativity between hydrogen and halogen bond in the XY···HNC···XY (X, Y = F, Cl, Br) complexes

The cooperativity between hydrogen and halogen bonds in XY···HNC···XY (X, Y = F, Cl, Br) complexes was studied at the MP2/aug-cc-pVTZ level. Two hydrogen-bonded dimers, five hydrogen-bonded dimers, and ten trimers were obtained. The hydrogen- and halogen-bonded interaction energies in the trimers were larger than those in the dimers, indicating that both the hydrogen bonding interaction and the halogen bonding interaction are enhanced. The binary halogen bonding interaction plays the most important role in the ternary system. The hydrogen donor molecule influences the magnitude of the halogen bonding interaction much more than the hydrogen bonding interaction in the trimers with respect to the dimers. Our calculations are consistent with the conclusion that the stronger noncovalent interaction has a bigger effect on the weaker one. The variation in the vibrational frequency in the HNC molecule was considered. The NH antisymmetry vibration frequency has a blue shift, whereas the symmetry vibration frequency has a red shift. A dipole moment enhancement is observed upon formation of the trimers. The variation in topological properties at bond critical points was obtained using the atoms in molecules method, and was consistent with the results of the interaction energy analysis.

Theoretical studies on the structures and isomerization of silylenoid H2SiNaCl

Abstract The structures and isomerization of silylenoid H 2 SiNaCl were studied by ab initio molecular orbital theory at RHF/6-31G(d) and MP2/6-311G(d,p) levels. Three equilibrium structures and two isomeric transition states were located. Based on the MP2/6-311G(d,p) calculations, harmonic frequencies of various isomers were obtained and further single-point calculations were performed at the QCISD(T)/6-311G(d) and MP2/6-311+G(3df,2p) levels, respectively. G2(MP2) theory was used for calculations on energies. Isomerization paths for isomers were investigated by intrinsic reaction coordinate (IRC) calculations at MP2/6-311G(d,p) level. Changes (Δ H and Δ G ) of thermodynamic functions, equilibrium constant K ( T ), A factor and reaction rate constant k of the isomerization reaction among isomers of H 2 SiNaCl were calculated and then thermodynamic and kinetic properties were analyzed. The stability, reactivity and existence of various equilibrium structures were also discussed in this paper.

Theoretical investigations of the H···π and X (X = F, Cl, Br, I)···π complexes between hypohalous acids and benzene

The H···π and X (X = F, Cl, Br, I)···π interactions between hypohalous acids and benzene are investigated at the MP2/6-311++G(2d,2p) level. Four hydrogen-bonded and three halogen-bonded complexes were obtained. Ab initio calculations indicate that the X···π interaction between HOX and C6H6 is mainly electrostatically driven, and there is nearly an equal contribution from both electrostatic and dispersive energies in the case of XOH–C6H6 complexes. Natural bond orbital (NBO) analysis reveals that there exists charge transfer from benzene to hypohalous acids. Atom in molecules (AIM) analysis locates bond critical points (BCP) linking the hydrogen or halogen atom and carbon atom in benzene.

PARTIAL POTENTIAL ENERGY SURFACE AND ITS APPLICATIONS IN REACTIVE RESONANCES

The conception of partial potential energy surface (PPES) is presented in this paper. PPES can be abstracted from complete potential energy surface (CPES), therefore, it can be constructed with ab initio quantum chemical method. For the systems of H+H2→H2+H, I+HI→IH+I and I-+HI→IH+I-, the construction and applications of PPES are proposed as typical examples. It can be seen that the applications of PPES demonstrate remarkable virtues in the analysis of reaction mechanism and the formation of scattering resonance states.

Theoretical study on the isomeric structures and the stability of silylenoid (Tsi)Cl2SiLi (Tsi = C(SiMe3)3)

The structures and isomerization of silylenoid (Tsi)Cl2SiLi (Tsi = C(SiMe3)3) were studied by density functional theory (DFT) at the B3LYP/6‐31G(d) level. Four equilibrium structures and three isomeric transition states were located. The three‐membered ring and p‐complex structures, 1 and 2, are the two most stable forms. Two other local minima, the σ‐complex 3 and tetrahedron structure 4, should rearrange to 1 with very low barriers, and then to the most stable isomer 2. To exploit further the stability of silylenoid (Tsi)Cl2SiLi, the insertion reactions of 2 and silylene (Tsi)ClSi into the HF molecule have been investigated at the B3LYP/6‐31G(d) level, respectively. The results show that the insertion of 2 into HF is very similar to that of (Tsi)ClSi into HF, but the latter is more favorable. To probe the influence of the substituent Tsi on the stability of silylenoid (Tsi)Cl2SiLi, the isomers and insertion reaction of silylenoid CH3Cl2SiLi were investigated in a similar way of those with (Tsi)Cl2SiLi. The results indicate that silylenoid containing very bulky group Tsi exhibits unusual stability because of the severe steric hindrance produced by Tsi at the center to which it is attached.

Theoretical study on the one-carbon unit transfer from imidazolinium to 1,2-diaminobenzene

Abstract One-carbon unit transfer from 1-acetyl-3-methylimidazolinium to 1,2-diaminobenzene has been studied using PM3 method. The structures of the intermediates and transition states have been optimized. The results show that there are two pathways to transfer the one-carbon unit, and each pathway consists of six steps. They are the combination of two reactants, proton migration, splitting of five-membered ring, formation of benzimidazole ring, another proton migration and separation of C–N bond. And the proton migrating step is the rate limiting step.

THEORETICAL STUDY ON PARTIAL POTENTIAL SURFACE AND SCATTERING RESONANCE STATE OF THE ASYMMETRICAL H EXCHANGING X + H2O → XH + OH (X = Cl, F, H) REACTIVE SYSTEM

In the course of an extensive investigation aimed at understanding the detailed mechanism of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The system of concern is X + H2O → XH + OH (X = Cl, F, H), and it belongs to a type of asymmetrical H exchanging reaction. Because the concerned electronic number is quite small, it is usually regarded as a template constructed the model of theory or experiment. In this paper, compared with the symmetrical systems, we constructed the partial potential surfaces of asymmetrical systems in order to research their resonance states. All results are in good agreement with previous theoretical and experimental works.

Binding Properties of CO, NO, and O2 to P450 Heme: a Density Functional Study

The structural and binding properties of diatomic molecules CO, NO and O2 to P450 heme were investigated in two different models (labeled as M1 and M2) using density functional method at the B3LYP/6-31G(d) level. The effects of the serine residue near diatomic molecules XO were considered in the model M2. The results show that the serine residue near the heme enforced the binding of XO to heme. Frequency analysis indicates that the stretching vibrational frequency decreased as CO, NO, and O2 complex with heme.

THE PARTIAL POTENTIAL ENERGY SURFACE AND SCATTERING RESONANCE STATE OF THE STATE-TO-STATE REACTION Br + HBr(v) → BrH(v′) + Br

In this paper, the partial potential energy surface (PPESs) of the Br + HBr and Br- + HBr systems including the minimum energy path and the vibrational potential curves were constructed at MP2/6-311++G** level, based on the conception and constructing approach of the PPESs previously proposed. These results obtained from the PPESs were compared with those from the high resolved threshold photodetachment spectrum of the BrHBr- anion measured by Neumark et al., J Phys Chem94, 1377–1388, 1990. On the basis of the PPESs, the scattering resonance states of the Br + HBr(v) → BrH(v′) + Br state-to-state reaction were studied and the satisfactory results were obtained. Subsequently, we calculated the width and lifetime of the resonance states in this reaction by the one-dimensional square potential well model, and obtained some results consistent to the experiments.

Theoretical investigation on pentacoordinated silicon compounds of H3SiX (X=F, Cl, Br, I) with NH3

Abstract The halosilane–ammonia adducts H 3 SiX·NH 3 (X=F, Cl, Br) were studied with ab initio calculations at the G2(MP2) level. By following the G2(MP2) theory and using effective core potentials for F, Cl, Br, and I atoms, the adducts H 3 SiX·NH 3 (X=F, Cl, Br, I) were also calculated. The calculations show that each halosilane can form two kinds of adducts with NH 3 . One of them is an axial position adduct and the other is a Si–X bond side-adduct. The former is more stable and easy to be formed. The bonding properties of all adducts were analyzed and the influences of various halogen atoms on structures and stability of adducts were discussed in this paper. It is predicted that adducts of H 3 SiX (X=Cl, Br, I) with ammonia or amines will give conducting solutions in solvents, which is well agreed with the experimental results.