取代基(NH2,OH,F)对锂氟类硅烯构型及稳定性的影响

用从头计算方法研究了3种锂氟类硅烯R2SiLiF(R=NH2,OH,F)各异构体的构型和能量.由于取代基NH2,OH和F与Si的共轭作用,这3种类硅烯的三元环构型的热稳定性下降,其下降程度按取代基排列为NH2＞OH＞F.因取代基R与Li原子间的相互作用,形成2个LiASiF(A=N,O,F)四元环,该四元环构型是这3种类硅烯的各异构体中最稳定的一种,其稳定程度按取代基排列为F＞OH＞NH2.取代基的诱导效应则影响各类硅烯的线性构型的热稳定性.     

钠卤类硅烯的结构与稳定性

本文用RHF/STO-3G解析梯度方法研究了钠卤类硅烯H2SiNaX(X=F,Cl)势能面的主要特征, 得到了它们的几种平衡构型及其异构化的过渡态构型。与锂卤类硅烯相似, 三元环构型和P-配合物构型是最稳定的构型; 其它的两种构型-σ-配合物和经典"四面体", 也是势能面上的极值点, 但能量相对较高, 不稳定。文中对各构型的特点进行了分析。     

钠氟类硅烯插入RH键(R=F,OH,NH2,CH3)反应的理论研究

用密度泛函方法研究了钠氟类硅烯插入R_H键(R=F,OH,NH2,CH3)的反应机理.4个反应的机制类似,反应经历了类硅烯的亲电接近、亲核插入和取代三个阶段之后,形成中间络合物,4个反应的势垒分别为0.9,61.7,114.6和190.6kJ/mol(经零点能校正).中间络合物可以解离为取代硅烷和NaF,这是一个无过渡态的过程.反应能分别是-122.6,-96.3,-6.8和50.2kJ/mol.     

类硅烯H2SiClBeCl的结构及异构化反应

用DFT和QCISD方法研究了类硅烯H2SiClBeCl的构型与异构化反应. 结果表明, 类硅烯H2SiClBeCl有三种平衡构型, 其中四面体构型能量最低, 是其存在的主要构型. 对平衡构型间异构化反应的过渡态进行了计算, 求得了转化势垒. 计算模拟了最稳定构型的红外光谱.     

不饱和类硅烯H2C=SiNaF的DFT研究

用密度泛函理论方法, 在B3LYP/6-31+G(d, p)水平上研究了不饱和类硅烯H2C=SiNaF的结构. 结果表明, 不饱和类硅烯H2C=SiNaF共有四种平衡构型, 其中非平面的p-配合物型构型能量最低, 是不饱和类硅烯H2C=SiNaF存在的主要构型. 对平衡构型间异构化反应的过渡态进行了计算, 求得了转化势垒. 计算预言了最稳定构型的振动频率和红外强度.     

不饱和类硅烯H_2CSiNaCl的密度泛函理论研究

采用密度泛函理论方法,在B3LYP/6-311G(d,p)水平上研究了不饱和类硅烯H2CSiNaCl的结构.结果表明,不饱和类硅烯H2CSiNaCl共有4种平衡构型,其中非平面的p-配合物型构型能量最低,是不饱和类硅烯H2CSiNaCl存在的主要构型.对平衡构型间异构化反应的过渡态进行了计算,求得了转化势垒.计算预言了最稳定构型的振动频率和红外强度.     

不饱和类硅烯H2C＝SiMBr (M＝Li, Na)的DFT研究

采用密度泛函理论方法, 在B3LYP/6-311G (d,p)水平上研究了不饱和类硅烯H₂C＝SiMBr (M＝Li, Na)的结构. 结果表明, 不饱和类硅烯H₂C＝SiLiBr与H₂C＝SiNaBr各有三种平衡构型, 其中非平面的p-配合物型构型能量最低, 是这两种不饱和类硅烯存在的主要构型. 对平衡构型间异构化反应的过渡态进行了计算, 求得了转化势垒. 计算预言了最稳定构型的振动频率和红外强度.     

不饱和类硅烯H2C=SiNaCl的密度泛函理论研究

采用密度泛函理论方法,在B3LYP/6-311G(d,p)水平上研究了不饱和类硅烯H2C=SiNaCl的结构.结果表明,不饱和类硅烯H2C=SiNaCl共有4种平衡构型,其中非平面的p-配合物型构型能量最低,是不饱和类硅烯H2C=SiNaCl存在的主要构型.对平衡构型间异构化反应的过渡态进行了计算,求得了转化势垒.计算预言了最稳定构型的振动频率和红外强度.     

类硅烯的结构与反应性的理论研究——Ⅰ.类硅烯H_2SiLiCl的构型及其异构化

本文用RHF/3-21G解析梯度方法研究了类硅烯H_2SiLiCl的结构,得到了三个平衡构型和两个异构化的过渡态构型,并用6-21G基组估计了能量,对其化学性质也进行了评价。计算结果表明,H_2SiLiCl的三元环构型是最稳定的几何构型;而它的经典四面体构型是不存在的。文中分析了各构型的特点,给出了电荷分布和前线分子轨道。此外,与H_2SiLiF进行了比较。对聚硅烷反应机理作了初步探讨。     

锂氟类硅烯与乙烯加成反应的理论研究

用从头计算方法研究了锂氟类硅烯与乙烯的加成反应Ｈ_２ＳｉＬｉＦ＋Ｃ_２Ｈ_４→Ｈ_２ＳｉＣ_２Ｈ４＋ＬｉＦ．该反应的过渡态和类卡宾与乙烯的反应相似。反应前后的能量差经零点能校正后仅为－２．４ｋＪ／ｍｏｌ（ＭＰ２／６－３１Ｇ￣＊／／６－３１Ｇ￣＊）．本文分析了孩反应的热力学和动力学性质，计算了反应热力学函数的变化、平衡常数、Ａ因子以及速率常数。     

Effect of Alkyl,Aryl, and <Emphasis Type="Italic">meso</Emphasis>-Aza Substitution on the Thermal Stability of BODIPY

The effect of peripheral alkyl, aryl, and meso-aza substitution on the thermal stability of BODIPYs in an argon or oxygen atmosphere has been analyzed using thermogravimetric study results. It has been shown that an increase in the length of 2,6-alkyl substituents to seven carbon atoms is accompanied by the growth of BODIPY thermal stability by 80°C. The greatest increase in the destruction temperature of BODIPY (by 100°C) is attained via the introduction of phenyl groups in the 1,3,5,7-positions of its dipyrromethenmethene framework. meso-Aza substitution does not almost produce any effect on the thermal stability of BODIPY dyes. The BODIPY destruction beginning temperature decreases by 60–90°C in the presence of air oxygen. The thermal stability of BODIPY tends to decrease with reducing degree and symmetry of alkyl substitution in the dipyrromethene framework. A lower thermal stability of BODIPY in comparison with zinc(II) dipyrromethenates is due to the participation of fluorine atoms in intramolecular redox processes.     

Theoretical study of the thermal rearrangement of chloromethylsilanes, and its mechanism

The thermal rearrangement reactions of chloromethylsilane, (chloromethyl)dimethylsilane, and (chloromethyl)vinylsilane have been studied by use of the density functional theory method at the B3LYP/6-311G(d, p) level. The structures of the reactants, transition states, and the products were determined and fully optimized. The geometries of the different stationary points and the harmonic vibrational frequencies were calculated at the same level. The results showed that thermal rearrangement of the chloromethylsilanes occurred via one pathway. The chlorine atom migrated from the carbon atom to the silicon atom, and the hydrogen atom migrated simultaneously from the silicon atom to the carbon atom through a double-three-membered-ring transition state, forming methylchlorosilane, trimethylchlorosilane, and vinylmethylchlorosilane. The energy barriers of the three rearrangements calculated at the B3LYP/6-311G(d, p) level were 217.4, 201.6, and 208.7 kJ mol^?1, respectively. The effects of alkyl substituents on silicon atom are discussed. Changes of thermodynamic functions, equilibrium constant, and reaction rate constant were calculated in accordance with Eyring transition-state theory over the temperature range 400–1,500 K.     

Lewis acid-promoted cycloaddition reaction of cyclopropanes with allylsilanes

The treatment of cyclopropanes having donor and acceptor substituents at the vicinal positions on the cyclopropane ring with a Lewis acid readily generates a 1,3-zwitterion, which reacted with allylsilanes to produce cycloadducts and allylic products. It was found that the yield of the cycloadduct depends on the steric demand of the alkyl substituents on the silicon atom.     

Chelate von Chinolin-8-ol-Derivaten. VIII. Säure- und Komplexstabilitätskonstanten alkyl- bzw. alkenylsubstituierter Chinolin-8-ole

Chelates of 8-Quinolinol Derivatives. VIII. Acid and Complex Stability Constants of Alkyl and Alkenyl Substituted 8-Quinolinols For a series of 7-substituted alkyl and alkenyl 8-quinolinols as well as 2-, 5-, and 7-methyl-8-quinolinols the acid constants and the stability constants of the nickel and zinc chelates were determined potentiometrically in 75 vol-% dioxane-water mixture. Methyl groups, as expected, increase the basicity of both donor atoms of the 8-quinolinols, whereas alkyl substituents in 7-position cause a decrease in basicity of the quinoline N-atom. The influence of substituents on the complex stability is only small.     

Insecticidal potency of certain organosilicon compounds

A small series of organosilicon compounds were screened for efficacy against the housefly Musca domestica. The activity of organosilicon compounds is attributed to the silicon atom, the presence of halogens and the alkyl groups.     

The radiation yields of radicals in solid organic substances containing heteroatoms

EPR has been used to measure the radiation yields of radicals (G_R) in various classes of organic compounds containing heteroatoms: dialkyl disulfides, diphenyl- and dibenzyl disulfide, alkyl derivatives of thiophene, thiophenecarboxylic acids, halogen derivatives of thiophene, and saturated heterocyclic compounds containing nitrogen, oxygen, and sulfur atoms. It has been shown that 1) G_R=0.2–1 per 100 eV in saturated disulfides and cyclic sulfides, while G_R=3–8 per 100 eV in the corresponding hydrocarbons, alcohols, oxides, and alkyleneimines; 2) the introduction of a sulfur atom into aromatic compounds does not alter the radiation stability; 3) disturbance of the conjugation of halogen atoms and of the carboxyl group with the thiophene ring leads to a decrease in the radiation stability. It is suggested that the increased stability of sulfur-containing compounds may be due to the excitation of the electrons in the S atom at the d-orbitals, which lie appreciably lower in the sulfur atom than in the atoms of oxygen, nitrogen, and carbon, and the subsequent dissipation of the excitation energy.     

Thermal properties of ligands, salts and metal complexes of linear oligopyrroles

The effect of structure on the thermal properties of dipyrrolylmethanes, dipyrrolylmethenes, bis (dipyrrolylmethenes), their salts, and chelates is analyzed proceeding from the results of thermogravimetric analysis. The common tendency is a decrease in the thermal stability of compounds with a disturbed symmetry of alkyl substitution of ligands and with a higher degree of their alkylation, with the increased size of alkyl substituents, with the nitrogen atom in the five-member cycles replaced by S or O. The opposite effect occurs at the change in the mode of attaching methylene spacer in going from 2,2′- to 3,3′-bis(dipyrrolylmethenes). The effects of the themostabilization of the ligands of linear oligopyrroles in the composition of chelates and HBr salts are evaluated quantitatively.     

Intra- and intermolecular hydrogen bonds in alkyl and silyl ethers: experimental and theoretical analysis

We have investigated the electronic impact of the R protecting group (TBS or PMB) in the conformational equilibrium of alpha-methyl substituted alcohols 1 (R = TBS) and 2 (R = PMB). The conformational analysis and (1)H NMR experiments for alcohols 1 and 2 reflect the tendency for the existence of hydrogen-bonded conformations. The intrinsic low basicity of silyl ethers does not affect the capacity of the oxygen attached to the silicon atom in forming intramolecular hydrogen bonds. We showed that the extents of the hydrogen bonds in silyl and alkyl ethers are determined by several properties, such as orbital interactions, lone pair hybridizations, and lone pair energies, and not just by the electronic occupancy of the donor atom. The populational analysis of NBO allowed understanding the intra- and intermolecular hydrogen bonds between the OH group and oxygen bonded to silicon as well as to alkyl ethers, concluding that there are distinct lone pair contributions.     

Mechanisms of thermal decomposition of organic monolayers grafted on (111) silicon

The thermal stability of different organic layers on silicon has been investigated by in situ infrared spectroscopy, using a specially designed variable-temperature cell. The monolayers were covalently grafted onto atomically flat (111) hydrogenated silicon surfaces through the (photochemical or catalytic) hydrosilylation of 1-decene, heptadecafluoro-1-decene or undecylenic acid. In contrast to alkyl monolayers, which desorb as alkene chains around 300 degrees C by the breaking of the Si-C bond through a beta-hydride elimination mechanism, the alkyl layers functionalized with a carboxylic acid terminal group undergo successive chemical transformations. At 200-250 degrees C, the carboxyl end groups couple forming anhydrides, which subsequently decompose at 250-300 degrees C by loss of the functional group. In the case of fluorinated alkyl chains, the C-C bond located between CH2 and CF2 units is first broken at 250-300 degrees C. In either case, the remaining alkyl layer is stable up to 350 degrees C, which is accounted for by a kinetic model involving chain pairing on the surface.     

Influence of the nature of the central atom of onium cations on the rate and selectivity of processes of their one-electron reduction

It was shown that the rate and selectivity of irreversible processes of electrochemical and chemical reduction of onium cations of elements of groups V-VII, containing alkyl and aryl substituents, increase with increasing principal quantum number of the central atom of the cation. This pattern is explained on the basis of the Marcus theory by a decrease in the energy of heterolytic dissociation of the bonds of the substituent to the central atom of the cation, leading to a decrease in the free energy and energy of reorganization of the reaction, as well as to an increase in their rate and selectivity.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 4, pp. 468–470, July–August 1987.