共查询到20条相似文献,搜索用时 46 毫秒
1.
利用滴定量热技术并结合适当的热力学循环测定了乙腈溶液中7个取代的N-亚硝基吲哚化合物中N—NO键的异裂能和均裂能, 能量范围分别为206.1~246.2 kJ/mol和119.1~124.6 kJ/mol. 表明N-亚硝基吲哚均裂释放NO自由基(NO·)比异裂释放NO正离子(NO+)要容易得多, 通过热力学循环得到的相应自由基负离子中N—NO键的异裂能和均裂能的能量范围分别为25.5~34.4和5.0~40.5 kJ/mol, 表明所研究化合物的自由基负离子在室温下很不稳定. 相似文献
2.
利用滴定量热技术并结合适当的热力学循环测定了乙腈溶液中7个S-亚硝基-N-乙酰基-D,L-青霉胺二肽化合物中S—NO键的异裂能和均裂能, 其能量范围分别为234.5—246.2 kJ/mol和101.6—122.1 kJ/mol. 结果表明, 所研究的亚硝基硫醇化合物更容易通过S—NO键的均裂释放NO自由基(NO·). 通过热力学循环对7个亚硝基硫醇化合物自由基负离子中S—NO键的异裂能和均裂能进行估算, 能量范围分别为19.2—35.5 kJ/mol和-4.2—22.6 kJ/mol, 表明这些自由基负离子在室温下不稳定, 容易通过S—NO键的异裂释放出NO-. 相似文献
3.
本文选取10个取代的亚硝酸苄(醇)酯化合物, 通过滴定量热和电化学方法, 结合热力学循环, 研究了其在乙腈溶液中的NO化学亲和势, 即O—NO键的均裂能和异裂能. 相似文献
4.
《中国科学:化学》2016,(6)
铱氢络合物是诸多铱催化反应中的催化剂和关键中间体,Ir–H键的断裂与生成在这些反应中往往起到至关重要的作用.本文利用密度泛函方法(DFT)对多种茂基配位的铱氢络合物的铱氢键均裂能和异裂能(负氢解离)进行了系统研究.计算发现,铱中心贫电子有利于Ir–H键的均裂,而吸电子基团以及强p电子受体有利于减弱Ir中心电子密度.刚性螯环以及大位阻取代基可以通过释放空间位阻进一步减小其键能.而如2-苯基吡啶、联吡啶配体等配位的铱氢化合物,由于Ir中心d轨道可以与这些配体的芳香体系形成大p键,因此降低了这些物种的H~-解离焓.烯烃配体有利于均裂过程,却不利于异裂的H~-解离.膦配体对均裂过程影响不大,但是可以大大减小H~-解离焓.贫电子的B原子,有利于均裂,因会形成Ir–H–B的氢桥键,不利于解离H~-.Si原子相对富电子,对这两个过程均不利. 相似文献
5.
合成了α-位有第V、Ⅵ主族元素杂正离子取代基的甲苯系列(1)和苯乙酮系列(2)共11个Ylide前体化合物,用重迭指示剂法首次测定了其在二甲亚矾(DMSO)溶剂中的酸性解离常数PKa,同时结合碳负离子(即Ylide)氧化电位的测定,通过热力学循环估测了它们的气相均裂键能(BDE).根据这些PKa和BDE数据,对16个Ylide前体化合物的C-H键的均裂能和异裂能进行了比较,并讨论了a-杂正离子取代基对相关的Ylide和类-Ylide自由基的热力学稳定性的影响及结构效应 相似文献
6.
7.
合成了α-位有第ⅤⅥ主族元素杂正离子取代基的甲苯系列(1)和苯乙酮系列(2)共11个Ylide前体化合物,用重迭指示剂法首次测定了其在二甲亚砜(DMSO)溶剂中的酸性解离常数pK,同时结合碳负离子(即Ylide)氧化电位的测定,通过热力学循环估测了它们的气相均裂键能(BDE)根据这些pKa和BDE数据,对16个Ylide前体化合物C-键的均裂能和异裂能进行了(BDE),根据这些pKa和BDE数据, 相似文献
8.
基于平均影响值的反向传播神经网络方法用于提高密度泛函理论计算Y—NO键均裂能精度 总被引:1,自引:0,他引:1
将基于平均影响值(Mean impact value,MIV)的反向传播神经网络(Back propagation neural netowrk,BPNN)(MIV-BPNN)方法用于提高密度泛函理论(Density functional theory,DFT)计算Y—NO(Y=N,S,O及C)键均裂能的精度.利用量子化学计算和MIV-BPNN联合方法计算92个含Y—NO键的有机分子体系的均裂能.结果表明,相对于单一的密度泛函理论B3LYP/6-31G(d)方法,利用全参数下的BPNN方法计算92个有机分子均裂能的均方根误差从22.25 kJ/mol减少到1.84 kJ/mol,而MIV-BPNN方法使均方根误差减少到1.36 kJ/mol,可见B3LYP/6-31G(d)和MIV-BPNN联合方法可以提高均裂能的量子化学计算精度,并可预测实验上无法获取的均裂能值. 相似文献
9.
化学键的键裂能(也称离解能)定义为在标准条件下:键均裂前后各个物种生成热的代数和,即:DH~0(R—X)=△tH_(208)~0(X·())+△fH_(298)~0(R·())—△fH_(298)~0,(RX())(1) 因此测量化学键的键裂能等价于测量自由基的生成热。Benson等经过近三十年,准确测 相似文献
10.
Δ-和Λ-[Ru(bpy)2(HPIP)2+两种异构体对小牛胸腺DNA不同键合速率的CD光谱证明 总被引:2,自引:0,他引:2
Wilson[1]于1997年发表了关于DNA导电性的评论性文章, 介绍了各种学派的观点. 争论焦点在于DNA是否为导体. 将两种配合物键合于DNA作为接头, 通过研究电子转移可确定DNA是否为导线, 其中配合物和DNA键合模式是研究的关键. Barton[2]和Norden[3]均认为2+ 配合物能强烈插入DNA中. 我们[4]曾从改变辅助配体角度出发, 研究2+和DNA的作用, 结果证明2+具有更强的插入能力, 并结合文献把键合模式归纳为3类, 即静电键合、沟面键合和插入键合[5]. 最近, 我们报道了新体系2+/DNA/2+(bpy=2,2′-bipyridine), 其中2+和2+均可插入DNA中. 2+是光诱导电子给予体, 2+是电子接受体, 荧光光谱证明前者的电子通过DNA中的π电子转移给后者, 导致后者荧光猝灭, 结果支持DNA是导线的观点[6]. 2+中的PIP芳香环和DNA碱基芳环组成π电子的堆积力[7], 从而增强了对DNA的插入能力. 相似文献
11.
用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%. 相似文献
12.
Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields. 相似文献
13.
Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction
Laurent Gavara Thomas Boisse Jean-Pierre Hénichart Adam Daïch Philippe Gautret 《Tetrahedron》2010,66(38):7544-5571
In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments. 相似文献
14.
The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula. 相似文献
15.
Rebecca J. Burton Mandy L. CrowtherNeal J. Fazakerley Shaun M. FilleryBarry M. Hayter Jason G. KettleCaroline A. McMillan Paula PerkinsPeter Robins Peter M. SmithEmma J. Williams Gail L. Wrigley 《Tetrahedron letters》2013
The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines. 相似文献
16.
KMnO4-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields. 相似文献
17.
N. A. Nedolya 《Chemistry of Heterocyclic Compounds》2008,44(10):1165-1219
The review contains a concise historical account and information on the most significant researches undertaken by the staff
at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry
of Heterocyclic Compounds.
Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008. 相似文献
18.
A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL. 相似文献
19.
Regiospecific and direct imidation of the methyl C(sp3)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products. 相似文献
20.
A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions. 相似文献