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1.
Yu WS Cheng CC Cheng YM Wu PC Song YH Chi Y Chou PT 《Journal of the American Chemical Society》2003,125(36):10800-10801
The excited-state intramolecular proton transfer (ESIPT) reaction in five-membered N-H...N hydrogen-bonding systems has been explored through design and syntheses of a series of 5-(2-pyridyl) 1-H-pyrazoles 1a-d. The ESIPT mechanism was confirmed through spectroscopy, relaxation dynamics, and corresponding methylated analogues. The results demonstrate for the first time a unique system among ESIPT molecules, in which ESIPT incorporates an appreciably large energy barrier fine-tuned by the skeletal reorganization. This makes 1a-d systems ideal models for probing the reaction potential energy surface. 相似文献
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[reaction: see text] Proton transfer in ketonization of enolates is a critical step in a myriad of organic reactions. Its stereochemistry has been the object of our studies since we reported kinetic protonation from the less hindered face of the molecule under kinetic control some decades ago. Very recently, we have succeeded in reversing the stereochemistry using 2-pyridyl groups to deliver the proton. We now report intramolecular delivery by other moieties and control of intramolecular versus intermolecular proton delivery. 相似文献
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V.V.V.N.S. Rama Rao B.P.V. Lingaiah R. Yadla P. Shanthan Rao K. Ravikumar G.Y.S.K. Swamy K. Narsimulu 《Journal of heterocyclic chemistry》2006,43(3):673-679
1, 3‐Dipolar‐cycloaddition reaction of fluoro substituted 3‐aryl‐propynenitriles 1 with benzyl azide 2 afforded the expected 3‐benzyl‐5‐aryl‐3H‐[1,2,3]triazole‐4‐carbonitrile 3 and 1‐benzyl‐5‐aryl‐1H‐[1,2,3]‐triazole‐4‐carbonitrile 4 in good yield. However, 1,3‐dipolar cycloaddition of diazomethane 5 with 3‐aryl‐propynenitriles 1 resulted in the exclusive formation of N‐methyl‐pyrazole derivatives 6 and 7 . 相似文献
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Hossein Tavakol 《International journal of quantum chemistry》2011,111(14):3717-3724
Nine tautomers and eleven possible tautomeric interconversions of N′‐acetyl formohydrazide have been studied at B3LYP/6‐311++G** level of theory. From these calculations, optimized geometries, molecular parameters, IR frequencies, NMR chemical shifts, and energetic results are obtained. In all tautomers except tautomers 4, E isomer is more stable than Z isomer. Energetic data were used to calculate the energy barriers of tautomeric interconversions and very high energy barriers were obtained for all tautomeric interconversions. Moreover, study of solvent effects on relative stabilities of tautomers and transition states showed that they are similar to those in the gas phase. In addition, intermolecular proton transfer with the assistance of one to three water molecules has been studied and the results showed that activation barriers in water‐assisted tautomerism are in general lower than those in the gas phase. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
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Di Zhou Xiulin Zhu Jian Zhu Haishu Yin 《Journal of polymer science. Part A, Polymer chemistry》2005,43(20):4849-4856
Polymerizations of styrene with azobisisobutyronitrile initiation or thermal initiation have been performed in the presence of dithiocarbamates with different N‐groups, that is, benzyl 4,5‐diphenyl‐1H‐imidazole‐1‐carbodithioate ( 2a ), benzyl 1H‐1,2,4‐triazole‐1‐carbodithioate ( 2b ), benzyl indole‐1‐carbodithioate ( 2c ), benzyl 2‐phenyl‐indole‐1‐carbodithioate ( 2d ), benzyl phenothiazine‐10‐carbodithioate ( 2e ), benzyl 9H‐carbazole‐9‐carbodithioate ( 2f ), and benzyl dibenzo[b,f]azepine‐5‐carbodithioate ( 2g ). The results show that the structure of the N‐group of dithiocarbamates has significant effects on the activity of dithiocarbamates for the polymerization of styrene. 2a , 2b , 2c , 2d , and 2f are effective reversible addition–fragmentation chain transfer (RAFT) agents for the RAFT polymerization of styrene, and the polymerizations have good living characteristics. However, in the cases of 2e and 2g , the obtained polymers have uncontrolled molecular weights and broad molecular weight distributions. The polymerization rate is markedly influenced by the conjugation structure of the N‐group of the dithiocarbamate, and the polymerization rate of 2b is greater than that of 2a . For 2b , the rate of polymerization seems independent of the RAFT agent concentration. However, a significant retardation in the rate of polymerization can be observed in the case of 2c . 2d is more effective than 2c , and the substitution group of phenyl on this dithiocarbamate has obvious effects on the effectiveness of the controlled polymerization of styrene. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4849–4856, 2005 相似文献
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Yusuke Sugihara Padraig O'connor Per B. Zetterlund Fawaz Aldabbagh 《Journal of polymer science. Part A, Polymer chemistry》2011,49(8):1856-1864
Chain transfer to solvent has been investigated in the conventional radical polymerization and nitroxide‐mediated radical polymerization (NMP) of N‐isopropylacrylamide (NIPAM) in N,N‐dimethylformamide (DMF) at 120 °C. The extent of chain transfer to DMF can significantly impact the maximum attainable molecular weight in both systems. Based on a theoretical treatment, it has been shown that the same value of chain transfer to solvent constant, Ctr,S, in DMF at 120 °C (within experimental error) can account for experimental molecular weight data for both conventional radical polymerization and NMP under conditions where chain transfer to solvent is a significant end‐forming event. In NMP (and other controlled/living radical polymerization systems), chain transfer to solvent is manifested as the number‐average molecular weight (Mn) going through a maximum value with increasing monomer conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
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J. Geno Samaritoni Scott Thornburgh Paul R. Graupner David H. Cooper 《Journal of heterocyclic chemistry》2007,44(6):1389-1393
Novel N2‐arylated pyrano[2,3‐c]pyrazol‐6‐ones 2 can be prepared in a selective manner by generating the anion of 1 ( R?H ) with lithium hexamethyldisilazide in DMF and quenching with activated aryl halides. Sterically demanding groups such as phenyl as in 5 reduce reactivity significantly while electronwithdrawing substituents such as trifluoromethyl and phenyl at C4 of the pyranone ring as in 10 and 15 render the pyranone carbonyl particularly susceptible to attack by nucleophiles resulting in ring‐opening to give novel crotonyl derivatives. Proof of structure required a variety of nmr methods involving proton, carbon, and nitrogen nuclei. 相似文献
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Effects of introduction of α‐carboxylate,N‐methyl,and N‐formyl groups on intramolecular cyclization of o‐quinone amines: Density functional theory‐based study 下载免费PDF全文
Ryo Kishida Adhitya Gandaryus Saputro Ryan Lacdao Arevalo Hideaki Kasai 《International journal of quantum chemistry》2017,117(23)
o‐Quinone amines, which are relevant to various biological processes, can undergo spontaneous intramolecular cyclization (ring closure reaction by amino‐terminated hydrocarbon side chain) that deactivates them toward another possible reactions, that is, thiol binding. Density functional theory‐based calculation is employed for obtaining the potential energy curves along the C? N bond formation in the intramolecular cyclization of various o‐quinone amines, viz., dopaminequinone, dopaquinone, N‐methyl‐dopaminequinone, N‐formyl‐dopaminequinone, and the corresponding methylene‐inserted analogues. The activation barrier is decreased by introduction of α‐carboxylate and N‐methyl group whereas increased by introduction of N‐formyl group. A negative correlation between the activation barriers and the level of highest occupied molecular orbital is pointed out. Furthermore, the methylene‐inserted analogues show decreased activation barriers. This is explained by reduction of steric repulsion in the transition state. 相似文献
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《Journal of heterocyclic chemistry》2018,55(1):44-64
This review explores the heterocyclic family of N‐nitrophenyl pyrazoles and indazoles covering mainly their structural aspects, with special emphasis on the X‐ray diffraction data. NMR spectroscopy and the theoretical calculations will also be briefly summarized. The synthesis and reactivity aspects will be reported when they are specific to these compounds. 相似文献
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Eiichi Masumoto Hiroshi Maruoka Fumi Okabe Sho Nishida Yuki Yoshimura Toshihiro Fujioka Kenji Yamagata 《Journal of heterocyclic chemistry》2011,48(1):96-104
Dihydropyridazinones 4a , 4b , N‐substituted dihydropyrazoles 5b , 5c , 5d , and O‐substituted pyrazoles 6a , 6b , 6c , 6d have been synthesized starting from spirocyclopropanepyrazole derivative 2 . Treatment of 2 with α‐chloro esters, e.g., methyl chloroacetate, ethyl chloroacetate, isopropyl chloroacetate, and tert‐butyl chloroacetate, in potassium carbonate/sodium iodide system caused ring opening and subsequent C‐ or N‐attack nucleophilic substitution to give the corresponding dihydropyridazinones 4a , 4b and N‐substituted dihydropyrazoles 5b , 5c , 5d . On the other hand, in the absence of sodium iodide, O‐substituted pyrazoles 6a , 6b , 6c , 6d were obtained from 2 via an O‐attack nucleophilic substitution. J. Heterocyclic Chem., 2011. 相似文献
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A. S. Brar Sukhdeep Kaur 《Journal of polymer science. Part A, Polymer chemistry》2006,44(5):1745-1757
The homopolymerization of N‐vinylcarbazole was performed with atom transfer radical polymerization (ATRP) with Cu(I)/Cu(II)/2,2′‐bipyridine (bpy) as the catalyst system at 90 °C in toluene. N‐2‐Bromoethyl carbazole was used as the initiator, and the optimized ratio of Cu(I) to Cu(II) was found to be 1/0.3. The resulting homopolymer, poly(N‐vinylcarbazole) (PVK), was formed after a monomer conversion of 76% in 20 h. The molecular weight as well as the polydispersity index (PDI) showed a linear relation with the conversion, which showed control over the polymerization. A semilogarithmic plot of the monomer conversion with time was linear, indicating the presence of constant active species throughout the polymerization. The initiator efficiency and the effect of the variation of the initiator concentration on the polymerization were studied. The effects of the addition of CuBr2, the variation of the catalyst concentration with respect to the initiator, and CuX (X = Br or Cl) on the kinetics of homopolymerization were determined. With Cu(0)/CuBr2/bpy as the catalyst, faster polymerization was observed. For a chain‐extension experiments, PVK (number‐average molecular weight = 1900; PDI = 1.24) was used as a macroinitiator for the ATRP of methyl methacrylate, and this resulted in the formation of a block copolymer that gave a monomodal curve in gel permeation chromatography. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1745–1757, 2006 相似文献
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Hiroyuki Hosomi Shigeru Ohba Yoshikatsu Ito 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):e144-e146
In the title four compounds, C13H11N·C7H4N2O6, (I), C15H15N·C7H4N2O6, (II), C16H17N·C7H4N2O6, (III), and C16H17N·C7H4N2O6, (IV), the donor and acceptor molecules are stacked alternately to form one‐dimensional columns. In (I), the N‐methyl group of the donor is nearly eclipsed with respect to one of the nitro groups of the neighboring acceptor in a column, whereas the N‐isopropyl, N‐butyl and N‐isobutyl groups are in anti positions with respect to one of the nitro groups of the neighboring acceptor in compounds (II)–(IV). 相似文献
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Thomas Steiner Antoine M. M. Schreurs Martin Lutz Jan Kroon 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):577-579
The title compounds contain very short intramolecular hydrogen bonds of the type C—O—H?O—N. The O?O distances are 2.425 (2) Å in picolinic acid N‐oxide (2‐carboxypyridine N‐oxide), C6H5NO3, (I), and 2.435 (2) Å in quinaldic acid N‐oxide (2‐carboxyquinoline N‐oxide), C10H7NO3, (II). In (II), this is associated with slight molecular distortion from planarity, while in (I), such an effect cannot be observed because the molecule crystallizes on a mirror plane. 相似文献
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The preparations of 4‐ and 5‐nitro‐1‐vinylimidazole ( 2 and 7 ) are described. Selective reduction of the nitro group using Fe/dil.HCl is achieved for the 4‐nitro derivative but this is not effective when ethoxymethylenemalononitrile is used to trap the amine. For 5‐nitroimidazole studies the N‐vinyl substituent is kept masked as a 2‐chloroethyl group, which remains unchanged during catalytic reduction of the nitro function (Pd/C), and is revealed by HCl elimination at a later stage. In this way, the 1‐deazapurine 13 and the tricyclic derivative 14 have been prepared. 相似文献
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M. Zupan V. Pirc A. Pollak B. Stanovnik M. Tier 《Journal of heterocyclic chemistry》1974,11(4):525-528
The free energies of activation about the =CH? NMe2 bond in N′-heteroaryl N,N-dimethylformamidines have been found in the range from 15.6 kcal/mole to 23 kcal/mole. 相似文献
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Transformation of N‐alkylated anilines to N‐aryloxamates was studied using ethyl 2‐diazoacetoacetate as an alkylating agent and dirhodium tetraacetate (Rh2(OAc)4) as the catalyst. The general applicability of the reaction as a synthetic method for N‐aryloxamates was studied with a number of substituted N‐alkylated anilines. The results revealed that the oxamate was formed by a radical reaction with molecular O2 and Rh2(OAc)4 as initiator. 相似文献