Quantum-Chemical Investigation of Intermediates in the Addition of Phenylsulfenium Cation to Substituted Acetylenes

The reaction paths for the transformations of substituted acetylenes (X—CC—Y; X, Y = H, Me, Ph, CN) in reaction with phenylsulfenium cation were studied by quantum-chemical methods. It was shown that the reactions take place with the formation of acyclic and cyclic cationic intermediates. The factor that determines the structure and characteristics of these cations is the induction and polarizing action of the substituents in the acetylenes and to a lesser degree their electron-donor characteristics. The resonance effect of the phenyl substituent has a predominantly levelling action on the distribution of charges.     

N,N-二(2-苯并咪唑亚甲基)甲胺高氯酸盐的晶体和电子结构

合成了三齿配体N,N-二(2-苯并咪唑亚甲基)甲胺(MN3)的高氯酸盐.对该化合物进行了元素分析、紫外和红外表征;采用X射线衍射方法测定了该化合物的晶体结构,依据晶体结构数据使用G98程序对配体(MN3)进行了量子化学计算.     

A quantum-chemical study of regioselectivity of indolization of some unsymmetrical ketone phenylhydrazones

The heat of formation (H _f) of unsymmetrical ketone phenylhydrazones and their enehydrazine tautomers was calculated by the semi-empirical quantum-chemical AM1 method. It is concluded that from H _f values it is possible to judge the regioselectivity of indolization of unsymmetrical ketone phenylhydrazones.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 220–221, January, 1993.     

An electronic structure investigation of the BNO-BON-NBO system

The potential energy hypersurface of the ground triplet states of the BNO-BON-NBO system has been investigated using traditional ab initio electronic structure theory. The molecules studied have the molecular formula BON and include three linear and three angular species, and two transition states for the isomerization of an angular N-B-O to an angular B-O-N and a linear B-NO, respectively. All stationary points on the BNO-BON-NBO isomerization potential energy surface have been characterized employing UMP2, UMP4, and Gaussian-2 (G2) theory with the 6-311G(d), 6-311G(2d), and TZ2P basis sets. The isomerization for an angular N-BO to the linear B-NO has a lower energy barrier than that of the former to an angular B-ON. Energetics are presented with G2 energies. Two sets of resonance structures for both bent B-NO (boron nitrosyl) and B-ON (boron isonitrosyl) were proposed and the bonding in the two species was analyzed. For the purpose of comparison, the density functional theory based hybrid methods B3LYP/6-311G(d) and B3LYP/TZ2P have also been applied to both geometry optimization and single-point calculations. It is found that the B3LYP prediction of the nature of the linear B-O is contradictory to that made by all MPn(n = 2 and 4) calculations. The cause for this contradiction is discussed.     

Facts and artifacts about aromatic stability estimation

The stability of a set of 105 five-membered π-electron systems (involving aromatic, non-aromatic and anti-aromatic species) was evaluated using six isodesmic reactions of which two belong to the subclass of homodesmotic reactions, which are based on cyclic and acyclic reference systems. We demonstrate that the ‘Resonance Energies’ derived from isodesmotic schemes have obvious flaws and do not correct or cancel other contributions to the energy, such as the changes of hybridization, homoconjugation of heterosubstituted cyclopentadienes, conjugative interactions of CC or CX (X=N or P) with a π or pseudo π orbital at Y (Y=O, S, NH, PH), strain, etc. as effectively as possible. Likewise, ‘aromatic stabilization energies (ASE)’ derived from homodesmotic schemes based on the acyclic reference compounds do not give satisfactory results. We strongly recommend that only cyclic reference compounds should be used for ASE and other aromaticity evaluations. The analysis is based on ab initio optimized geometries at B3LYP/6-311+G^∗∗.     

Spin-orbit ab initio investigation of the ultraviolet photolysis of diiodomethane.

The UV photodissociation (<5 eV) of diiodomethane (CH(2)I(2)) is investigated by spin-orbit ab initio calculations. The experimentally observed photodissociation channels in the gas and condensed phases are clearly assigned by multi-state second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space-state interaction potential energy curves. The calculated results indicate that the fast dissociations of the first two singlet states of CH(2)I(2) and CH(2)I--I lead to geminate-radical products, CH(2)I (.)+I((2)P(3/2)) or CH(2)I (.)+ I*((2)P(1/2)). The recombination process from CH(2)I--I to CH(2)I(2) is explained by an isomerization process and a secondary photodissociation reaction of CH(2)I--I. Finally, the study reveals that spin-orbits effects are significant in the quantitative analysis of the electronic spectrum of the CH(2)I--I species.     

六氢吡啶和氨形成的氢键团簇C5H10NH(NH3)n(n=1～3)结构的从头算研究

在RHF/6-31G(d)水平下,对C5H10NH(NH3)n(n=1～3)氢键团簇的平衡构型进行了从头算研究,优化得到各种可能的平衡构型.C5H10NH(NH3)为线型氢键结构,而C5H10NH(NH3)2为三元环结构,C5H10NH(NH3)3为四元环结构.在MP2/6-31G(d)//B3LYP/6-31G(d)水平下,对最稳定构型C5H10NH(NH3)n(Ⅰ)(n=1～3)的分子轨道进行布居分析,并且对相应的占据轨道进行指认.C5H10NH(NH3)n(Ⅰ)(n=1～3)垂直电离势的计算结果表明,形成氢键团簇后,分子的垂直电离势降低.     

The Weak Interaction on CO2 …CO van der Waals Complex : A Theoretical Study

The geometries of van der Waals complex CO2…CO were optimized at DFT and second-order Moller-Plesset perturbation(MP2) levels with the large basis set,three stable structures were found.The most stable structure has a T-shape geometry in which the CO lies along the C2 axis of CO2,with the two C atoms direct contact and R(C…C)=0.3227nm.The corresponding energies of the most stable structure were calculated by means of MP2,MP4D,MP4DQ,MP4SDTQ,MP4SDQ,CCSD and CCSD(T) methods,The BSSE (basis set superposition error) wads eliminated by the Boys-Bernardi counterpoise correction(CP) method.According to thermodynamics data.van der Waals complex CO2…CO can found at a low temperature and or a high pressure,There is a little charge transferred between the two interacted subunits.In the most stable structure,CO2 is the acceptor and CO is the donor.