Structures,vibrational spectra,and relative energetics of FC(O)ONO and FC(O)NO2 isomers at DFT and ab initio levels

The structural and vibrational parameters of FC(O)ONO and FC(O)NO₂ isomers were examined theoretically using the B3LYP/6-311+G(3df) and CCSD(T)/6-311G(d) methods. Four conformers of FC(O)ONO isomer and one FC(O)NO₂ isomer are found here. Among them, the trans–cis and cis–cis FC(O)ONO configuration are new conformers. The energetics were refined with G3//B3LYP and CBS-QB3 calculations. The trans–trans conformer of the FC(O)ONO isomer is found to be the lowest energy structure, with an estimated heat of formation of ?104.9 kcal mol^?1 at 0 K as determined from CBS-QB3 theory. The next lowest structure is the cis–trans FC(O)ONO lying 1.7 kcal mol^?1 above the trans–trans structural form. The highest energy structure is the FC(O)NO₂ isomer with a predicted heat of formation of ?84.8 kcal mol^?1. A comparison of the relative stability of the FCNO₃ isomers with the isomers of ClCNO₃ shows that the Cl analogues follow the same pattern of stability, as do the F isomers. However, the chlorine isomers are unstable relative to their fluorine analogues.     

Synthesis,Characterization and Reactions of 4‐Hydrazino‐2‐methylpyrimidino[4′5′:4,5]thiazolo[3,2‐a]benzimidazole

4‐Hydrazino‐2‐methylpyrimidino[4′,5′:4,5]thiazolo[3,2‐a]benzimidazole ( 4 ) was obtained from hydrazinolysis of the 4‐chloro derivative 3 with hydrazine hydrate. The hydrazino derivative 4 was further cyclized to the corresponding pyrazole 5 , pyrazolone 6 and 5‐methyl‐1,2,4‐triazolo[1″,5″:3′,4′]pyrimidino[5′,6′:5,4]‐thiazolo[3,2‐a]benzimidazole ( 9 ) and 5‐methy‐1,2,4‐triazolo[4″,3″:3′,4′]pyrimidino[5′,6′:5,4]thiazolo‐[3,2‐a]benzimidazole ( 10 ), respectively. The triazolo derivative 10 was isomerized to the triazolo derivative 9 under a variety of reaction conditions.     

Predictive abilities of scaled quantum-mechanical molecular force fields: application to 2-methylbuta-1,3-diene (isoprene)

The ab initio-based, scaled quantum-mechanical molecular force field (SQM-FF) analysis of the vibrational spectra of the s-trans and s-gauche conformers of 2-methylbuta-1,3-diene (isoprene), reported previously at the HF/6-31G//HF/6-31G computational level [Bock, et al. J Mol Struct 160: 337, 1987], has been updated in this article using a more complete set of experimental data on the s-gauche conformer along with revised results for the s-trans conformer obtained in the gas phase, in a low-temperature matrix, and in neat crystals. Geometrical parameters and the calculated wavenumbers derived from the SQM-FF at the MP2(FC)/aug-cc-pVDZ//MP2(FC)/aug-cc-pVDZ level are compared to experiment. The analyses performed are consistent with the presence of a twisted high-energy s-gauche conformer of isoprene.     

[Co(2,3-tri)(amp)Cl][ZnCl_4]体系中部分几何经式异构体的结构测定

利用单晶X射线衍射分析了Co23triampClZnCl423tri=N2Aminoethyl13propanediamineamp=2Aminomethylpyridine体系中的一异构体m3Co23triampClZnCl4·2.5H2O结构用二维核磁共振DQCOSY和NOESY技术联合解析了另两个异构体m2Co23triampClZnCl4及m4Co23triampClZnCl4在溶液中的结构。结构解析显示它们为该体系的三个几何经式异构体。解析的晶体结构属中心对称的空间群表明它是外消旋的对映体。     

New monomers and polymers via Diels-Alder cycloaddition

The series of new bis(naphthalic anhydrides) was prepared through Diels-Alder cycloaddition. The Diels-Alder cycloaddition was used as a synthetic route to new phenylated monomers as well as to polymers. All polymers synthesized revealed to be soluble in a wide range of organic solvents such as toluene, THF, chloroform, and displayed high thermostability. Therefore, they can be processed easily and are promising candidates for advanced coating systems as well as for electrooptical applications.     

1,3-和1,4-环己亚硝酸二酯电子轰击解离的结构效应

烷基亚硝酸二酯是一种重要的亚硝化剂,也是大气中NO_x污染物的来源之一,近年来引起了人们的广泛关注. 烷基亚硝酸二酯中两个ONO官能团对分子反应活性的影响以及在化学反应中的作用尚不清楚. 本文用电子碰撞电离质谱研究了1,3-环己亚硝酸二酯和1,4-环己亚硝酸二酯的解离过程. 实验结果发现两种结构异构体的分解产物不同：除了亚硝酸酯的特征碎片NO⁺(m/z=30)外,对于1,3-异构体,碎片离子m/z=43和71的丰度最高;而对于1,4-异构体,电子碰撞电离质谱谱图中解离产物m/z=29、57、85和97的强度较大. 对中性分子、分子离子以及中间产物的结构和电荷计算结果显示,1,3-环己亚硝酸二酯的分解清楚地显示出两步解离机制,即母体阳离子M⁺首先失去一个NO,然后中间离子(M-NO)⁺通过两个αC-βC键的断裂打开六元碳环;对于1,4-环己亚硝酸二酯,除了两步分解机制之外,还可以直接从母体阳离子M⁺发生αC-βC键的裂解. 研究结果有助于理解在大气反应及亚硝化合成反应中烷基亚硝酸二酯的分子结构对反应历程的影响.