A.A. Koridze, N. M. Astakhova, P. V. Petrovskii,
... 57Fe-enriched samples of ferrocene derivatives, α-ferrocenyl carbocations and carbonyl complexes with various σ- and π-hydrocarbon ligands. In the α-ferrocenyl carbocations the 57Fe resonances span a 1200 ppm range, ... in the stabilization. The 57Fe resonances in the carbocations [FcCH2][HSO4] (I), [FcCHMe][HSO4] (II), [FcCHPh][HSO4] ( ... their unbridged analogues. The 13C NMR spectra of carbocations V and VI reveal a temperature dependence due ... around the C(1)Cα exocyclic bonds. In carbocation VI the ruthenium atom effectively competes with the ...
Tópico(s): Metal complexes synthesis and properties
1983 - Elsevier BV | Journal of Organometallic Chemistry
Kenneth K. Laali, Maria A. Arrica, Takao Okazaki, Ronald G. Harvey,
A series of novel carbocations were generated from isomeric monoalkylated and dialkylated benz[a]anthracenes (BAs) by low-temperature protonation in FSO3H/SO2ClF. With the ... the C-7 or the C-12 protonated carbocations were observed (as the sole or major carbocation) in all cases. Protonation of the 12-methyl derivative (9) gave the C-7 protonated carbocation (9H+) as the kinetic species and the ipso-protonated carbocation (9aH+) as the thermodynamic cation. With the 12- ... sole species observed is the C-7 protonated carbocation (15H+). For 7-methyl-12-ethyl, 7-ethyl- ...
Tópico(s): Molecular Spectroscopy and Structure
2007 - American Chemical Society | The Journal of Organic Chemistry
B. Andes Hess, Lidia Smentek, Joseph P. Noel, Paul E. O’Maille,
... interplay of enzymes and the intrinsic reactivity of carbocation species at major branch-points along intramolecular cyclization ... Wagner-Meerwein rearrangements of the eudesm-5-yl carbocation during the cyclization of farnesyl pyrophosphate (FPP) catalyzed ... synthases. While the spirojatamane skeleton shares the same carbocation intermediate, this class of sesquiterpenes has not been ... for alternative rearrangements of the eudesm-5-yl carbocation, we carried out quantum mechanics (QM) analyses to ... states linking conformers of the eudesm-5-yl carbocation to the eremophilene, spirovetivane, and spirojatamane skeletons. Additionally, ...
Tópico(s): Allelopathy and phytotoxic interactions
2011 - American Chemical Society | Journal of the American Chemical Society
Gabriela L. Borosky, Kenneth K. Laali,
Structure−reactivity relationships and substituent effects on carbocation stability in benzo[a]anthracene (BA) derivatives have been studied computationally at the B3LYP/6-31G* and MP2/6-31G** levels. Bay-region carbocations are formed by O-protonation of the 1, ... process is energetically more favored as compared to carbocation generation via zwitterion formation/O-protonation, via single ... a radical cation, or via benzylic hydroxylation. Relative carbocation stabilities were determined in the gas phase and ...
Tópico(s): Free Radicals and Antioxidants
2006 - American Chemical Society | Chemical Research in Toxicology
David J. Hosfield, Yanming Zhang, D.R. Dougan, Alexei Broun, Leslie W. Tari, Ronald V. Swanson, John Finn,
... further demonstrate how nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme. Together, these FPPS ... further demonstrate how nitrogen-containing bisphosphonates mimic a carbocation intermediate to inhibit the enzyme. Together, these FPPS ... Fig 3A).Fig. 3Stereo illustration of the FPPS carbocation-binding site and structure-based three-metal ion ... with their negative dipoles directed toward the allylic carbocation-binding site. The nonmetal-ligated pyrophosphate oxygen that ...
Tópico(s): HIV/AIDS drug development and treatment
2004 - Elsevier BV | Journal of Biological Chemistry
... coordination sphere. W161 may stabilize the highly reactive carbocation generated during the reaction through quadrupole– charge interaction. ... site is required to protect the highly reactive carbocation intermediate, which must be shielded from solvent. C67 ... IPP, leading to the formation of an intermediate carbocation. Final deprotonation of the carbocation to form DMAPP could be accomplished via the ... help to reprotonate C67 after formation of the carbocation intermediate. This cluster is located in a region ...
Tópico(s): Enzyme Structure and Function
2001 - Springer Nature | The EMBO Journal
G. Ferguson, Lei Cheng, Lintao Bu, Seonah Kim, David J. Robichaud, Mark R. Nimlos, Larry A. Curtiss, Gregg T. Beckham,
... proposed reaction mechanisms for alcohol dehydration exhibit noncyclic carbocation intermediates or transition states that resemble carbocations, and several previous studies suggest that the tert- ... oxygen (i.e., an alkoxide). To determine if carbocations can exist at high temperatures in zeolites, where ... vapor-phase upgrading (∼500 °C), the stability of carbocations and the corresponding alkoxides were calculated with two ... tested are unreliable at finding minima for primary carbocations, and only secondary or higher carbocations can be ...
Tópico(s): Catalysis for Biomass Conversion
2015 - American Chemical Society | The Journal of Physical Chemistry A
Hans‐Ullrich Siehl, Thomas Müller,
... substitution β-substitution Solvolytic Studies α-silicon-substituted Carbocations in Solvolysis β-silicon-substituted Carbocations in Solvolysis α-disilanyl Carbocations in Solvolysis γ-silicon Effect δ-silicon Effect ... Substitution NMR Spectroscopic Characterization of α-silyl-substituted Carbocations 1-phenyl-1-trimethylsilylethyl Cation Diphenyl(trimethylsilyl)methyl ... the Tris(trimethylsilyl)cyclopropenylium Cation β-silyl-substituted Carbocations sp2-hybridized Carbocations Photochemical Generation and UV Characterization ...
Tópico(s): Inorganic and Organometallic Chemistry
1998 - Wiley | Patai's chemistry of functional groups
Elena Borodina, Huda Sharbini Kamaluddin, Florian Meirer, M. Mokhtar, Abdullah M. Asiri, Shaeel A. Al‐Thabaiti, S.N. Basahel, Javier Ruiz‐Martínez, Bert M. Weckhuysen,
... pool species consist of mainly highly methylated benzene carbocations at temperatures between 573 and 598 K, of both highly methylated benzene carbocations and methylated naphthalene carbocations at 623 K, and of only methylated naphthalene carbocations at temperatures between 673 and 773 K. The ... selectivity. In fact, monoenylic and highly methylated benzene carbocations are more selective to the formation of propylene, ... formation of the group of low methylated benzene carbocations and methylated naphthalene carbocations at higher reaction temperatures ( ...
Tópico(s): Chemical Synthesis and Characterization
2017 - American Chemical Society | ACS Catalysis
Hajime Sato, Bi‐Xiao Li, Taisei Takagi, Chao Wang, Kazunori Miyamoto, Masanobu Uchiyama,
... indicate that a sequential formation of secondary (2°) carbocations might be involved in some biosynthetic pathways, including ... we find that none of the putative 2° carbocation intermediates is involved in either of the biosynthetic pathways. In verrucosane biosynthesis, the proposed 2° carbocations (II and IV) in the early stage are bypassed by the formation of the adjacent 3° carbocations and by unusual skeletal rearrangement reactions, and in the later stage, the putative 2° carbocation intermediates (VI, VII, and VIII) are not present ...
Tópico(s): Natural product bioactivities and synthesis
2021 - American Chemical Society | JACS Au
Shani Zev, Prashant Kumar Gupta, Efrat Pahima, Dan Thomas Major,
Carbocations play key roles in classical organic reactions and have also been implicated in several enzyme families. A hallmark of carbocation chemistry is multitudes of competing reaction pathways, and ... to approach chemical accuracy for relative energies between carbocations. Here, we present an extensive study of the ... methods in describing the thermochemistry and kinetics of carbocations and their corresponding neutral alkenes both in the ... the findings in the gas-phase calculations of carbocations and alkenes, the best functionals are chosen and ...
Tópico(s): Enzyme Catalysis and Immobilization
2021 - American Chemical Society | Journal of Chemical Theory and Computation
Meng-En Chen, Shi‐Zhong Tang, Yue‐Hong Hu, Qin-Tong Li, Zhang‐Yan Gan, Jian-Wei Lv, Fu‐Min Zhang,
... of a limited amount of nitriles and producing carbocation intermediates via the C–H bond oxidation strategy ... in which a nitrile reacts with a reactive carbocation intermediate generally derived from alkyl alcohol, alkene, or ... acyl aza-quaternary carbon moiety from the tertiary carbocation intermediate.6–8 Such sterically hindered amides are ... C–H bond oxidation strategy for producing reactive carbocation intermediates can avoid the preparation of synthetic precursors ... transformation,29 it is challenging because the generated carbocation intermediate is highly unstable due to the destabilizing ...
Tópico(s): Synthesis and Biological Evaluation
2021 - Chinese Chemical Society | CCS Chemistry
Lanxuan Doan, Haruhiko Yagi, Donald M. Jerina, Dale L. Whalen,
... the reaction of water with the C-10 carbocation intermediate. Yet, the cis/trans ratio of tetrols from the reaction of the carbocation intermediate from the hydrolysis of chlorohydrin 5 is ... of diol epoxide 1, which hydrolyzes via a carbocation with the same connectivity as that formed in ... of chlorohydrin 5 yields a different distribution of carbocation conformations than that formed from the reaction of ... The energy barrier for the inversion of these carbocation conformations must be large relative to the energy ...
Tópico(s): Analytical Chemistry and Chromatography
2002 - American Chemical Society | Journal of the American Chemical Society
Guo‐Ping Yong, Chen Shen, Ya Qing Feng, Xuerui Zhang, Yumei Zhao,
... mild approach, we unprecedentedly synthesized three novel triarylmethyl carbocation radical salts, namely bisimidazo[1,2-a]pyridin-2-one-yl(2-pyridyl)methyl carbocation radical salt (1), bisimidazo[1,2-a]pyridin-2-one-yl(3-pyridyl)methyl carbocation radical salt (2), and bisimidazo[1,2-a]pyridin-2-one-yl(4-pyridyl)methyl carbocation radical salt (3). Single-crystal X-ray diffraction ... isomeric effects of pyridyl groups in the three carbocation radical salts are significant in the construction of ... chains consists of one repetitive unit having four carbocation radical moieties, giving a magnetic susceptibility value of ...
Tópico(s): Luminescence and Fluorescent Materials
2015 - Royal Society of Chemistry | CrystEngComm
Ji Duck Kim, Gyoonhee Han, Lak Shin Jeong, Hyun-Ju Park, Ok Pyo Zee, Young Hoon Jung,
... stability order of various alkyl, allyl, and benzyl carbocations was investigated using the novel technique for comparing the stability of carbocations in solution developed by using a simple CSI reaction with various ethers. The p-methoxycinnamyl carbocation was the most stable in our reaction system and the next stable carbocation was the p-methoxybenzyl carbocation. The stability of the other carbocations decreased with methacryl, t-butyl, cinnamyl, acryl, benzyl, 2° and allyl carbocations in that order.
Tópico(s): Chemical Reaction Mechanisms
2002 - Elsevier BV | Tetrahedron
Gregory M. Sandala, David M. Smith, Leo Radom,
... littorine to hyoscyamine. Two pathways involving radical and carbocation intermediates have been investigated in this regard, namely, ... of high energy for both the radical- and carbocation-based mechanisms (136.3 and 170.9 kJ ... 135.6 kJ mol−1). In contrast, the carbocation-based concerted pathway is found to be associated ... that its oxidation to generate the substrate-derived carbocation 3b ought to be facile. In an attempt ... the rearrangement barrier for both the radical- and carbocation-based concerted pathways, although the carbocation pathway continues ...
Tópico(s): Radical Photochemical Reactions
2008 - American Chemical Society | Journal of the American Chemical Society
... the various aspects of stabilities and reactivities of carbocations. The choice of an equilibrium constant for measuring the stability of a carbocation depends partly on experimental accessibility and partly on ... solvent. The majority of equilibrium constants measured for carbocation formation refers to the ionization of alcohols or ... kinetic methods for determining pKa and pKR for carbocations, by combining rate constants for their formation from ... rate constant for the reverse reaction of the carbocation with water, has provided the most important development ...
Tópico(s): Biochemical Acid Research Studies
2010 - Elsevier BV | Advances in physical organic chemistry
... chemical shifts and spin–spin coupling constants in carbocation chemistry. Calculation of NMR parameters, such as chemical ... constants has evolved into an important tool in carbocation chemistry as well as in related fields, such ... chemical shifts for a great structural variety of carbocations some difficulties have been encountered for vinyl cations. ... detailed information on structures and stabilization modes of carbocations, and have provided deeper insights into intriguing questions and long-standing controversies in carbocation chemistry. The everlasting need for better experimental tools ...
Tópico(s): Advanced NMR Techniques and Applications
2007 - Elsevier BV | Advances in physical organic chemistry
Jason B. Bialecki, Carl S. Weisbecker, Athula B. Attygalle,
... intermediate complex. The fragmentation of this [p-toluenesulfonamide/carbocation] complex eliminates p-toluenesulfonamide and releases the carbocation (Pathway B). Computations carried out by the Hartree- ... is more favorable. However, a peak for the carbocation is observed only when the carbocation formed is relatively stable. For example, the spectrum ... remarkably stable methylbenzyl cation. The peaks for the carbocations are weak or absent in the spectra of most of N-alkyl-p-toluenesulfonamides because alkyl carbocations, such as the decyl cation, rearrange to more ...
Tópico(s): Radioactive element chemistry and processing
2014 - American Chemical Society | Journal of the American Society for Mass Spectrometry
Abstract Carbocations are intrinsically reactive species, and in early studies of their generation and properties the more accessible with ... studies to include factors which tend to destabilize carbocations. By using the carbocations CH and C 2 H as reference ions, ... studied by their effect on the thermodynamics of carbocations, their effect on reactivities, and by the spectroscopic properties of long‐lived carbocations. Destabilized carbocations of this type are receiving increasing attention and ...
Tópico(s): Analytical Chemistry and Chromatography
1984 - Wiley | Angewandte Chemie International Edition
Gabriela L. Borosky, Kenneth K. Laali,
... structure–reactivity relationships and fluorine substitution effects on carbocation stability in benzo[a]pyrene (BaP), benzo[e] ... are reported. The relative energies of the resulting carbocations are examined and compared, taking into account the ... of the epoxides and diol epoxides leads to carbocation formation by barrierless processes. Charge delocalization modes in the resulting carbocations were deduced via NPA-derived changes in charges, ... on the basis of charge density at different carbocation positions. Thus, fluorine substitution at sites bearing negative ...
Tópico(s): Synthesis and Biological Evaluation
2007 - Royal Society of Chemistry | Organic & Biomolecular Chemistry
... role of quantum calculations in the field of carbocations is reviewed mainly over the past 10 years. ... theoretical methods to the prediction of hydrocarbon and carbocation energies is presented, showing where problems can be ... density functional theory methods. Gas‐phase stabilities of carbocations are discussed along with the interpretation of their ... hyperconjugation, conjugation, and aromaticity/antiaromaticity effects. Interesting new carbocation structures and new bifurcation mechanisms are featured, along ...
Tópico(s): Advanced Chemical Physics Studies
2011 - Wiley | Wiley Interdisciplinary Reviews Computational Molecular Science
Stephen G. Davies, Timothy J. Donohoe,
... of the chromium tricarbonyl unit to stabilise benzylic carbocations and oxonium ions is described. We have investigated ... of a nucleophile onto chromium tricarbonyl stabilised benzylic carbocations and oxonium ions is described. 1. Introduction 2. Evidence for the Chromium Tricarbonyl Stabilisation of Benzylic Carbocations 3. Acyclic Systems without ortho Substitution 3.1 Carbocations 3.2 Oxonium Ions 4. Bicyclic Complexes 4. ... Systems 5. ortho Substituted Acyclic Compounds 5.1 Carbocations 5.2 Oxonium Ions 6. Miscellaneous Applications of ...
Tópico(s): Synthesis and Biological Activity
1993 - Thieme Medical Publishers (Germany) | Synlett
Jian Lv, Qichao Zhang, Xingren Zhong, Sanzhong Luo,
Stable carbocations such as tritylium ions have been widely explored as organic Lewis acid catalysts and reagents in organic synthesis. However, achieving asymmetric carbocation catalysis remains elusive ever since they were first ... come from their limited compatibility, scarcity of chiral carbocations, as well as the extremely low barrier to ... We reported here a latent concept for asymmetric carbocation catalysis. In this strategy, chiral trityl phosphate is employed as the carbocation precursor, which undergoes facile ionic dissociation upon mild ...
Tópico(s): Synthetic Organic Chemistry Methods
2015 - American Chemical Society | Journal of the American Chemical Society
Paul C. Miklis, R. Ditchfield, Thomas A. Spencer,
An investigation of the interaction of carbocations with aromatic rings has been initiated by a computational study of complexation of methyl cation with benzene to determine if this is ... a practical, reliable approach for the study of carbocation−π interactions. Although none of the π complexes ... binding. With respect to the postulated stabilization of carbocation intermediates in biochemical reactions via π interactions with ... that very substantial stabilization can be afforded to carbocations positioned appropriately over any portion of a benzene ...
Tópico(s): Protein Structure and Dynamics
1998 - American Chemical Society | Journal of the American Chemical Society
Anubhav Kumar, Supratim Mondal, Shibdas Banerjee,
Carbocations are short-lived reactive intermediates in many organic and biological reactions that are difficult to observe. ... capture and nuclear magnetic resonance characterization of transient carbocations. We report here that water microdroplets can directly capture the fleeting carbocation from a reaction aliquot followed by its desorption ... spectrometry to detect a variety of short-lived carbocations (average lifetime ranges from nanoseconds to picoseconds) obtained ... microdroplets outperform organic microdroplets in the capture of carbocations. We provide a mechanistic insight demonstrating the survival ...
Tópico(s): Molecular Sensors and Ion Detection
2021 - American Chemical Society | Journal of the American Chemical Society
Giovanni Ghigo, Andrea Maranzana, Glauco Tonachini,
... two reaction pathways share an apparently identical intermediate carbocation. This has been dubbed the "memory effect", since the initial carbocation seems to "remember" its origin when undergoing further ... loss, multiphase rearrangements concertedly yield the two stablest carbocations, G and L. These carbocations are connected by a transition structure. The carbocation intermediates proposed in the literature do not correspond ... guided by geometrical aspects present in the starting carbocations. The dynamical study shows that (1) G and ...
Tópico(s): Free Radicals and Antioxidants
2013 - American Chemical Society | The Journal of Organic Chemistry
Gabriela L. Borosky, Kenneth K. Laali,
... understanding structure−reactivity relationships and substituent effects on carbocation stability in aza-polycyclic aromatic hydrocarbons, the epoxides, ... at the B3LYP/6-31G* level. Bay region carbocations were formed via the O-protonated epoxides in barrierless processes. Relative carbocation stabilities were determined in the gas phase and ... model method). Charge delocalization modes in the resulting carbocations were deduced by gauge-independent atomic orbitals (GIAO) ... ring positions bearing significant positive charge leads to carbocation stabilization by fluorine p-π back-bonding, fluorine ...
Tópico(s): Synthesis and Biological Evaluation
2005 - American Chemical Society | Chemical Research in Toxicology
Lei Wang, Wei Li, Jing Lu, Jingping Zhang, Hao Wang,
We have designed and synthesized a new carbocation precursor (carbinol) based on bis-pyrene derivative. The carbinol can be transformed to stable carbocations with quenched fluorescence and long wavelength absorption. The stable carbocations can be further used as fluoride anion detection ... chemical calculations and the results indicate that the carbocation mediated formation of C–F covalent bond leads to this dual responsive phenomenon. The bis-pyrene carbocations and corresponding F adduct was confirmed MALDI-TOF ...
Tópico(s): Fluorine in Organic Chemistry
2014 - Elsevier BV | Tetrahedron
Ken’ichi Takeuchi, Yasushi Ohga, Masayasu Yoshida, Keizo Ikai, Tadashi SHIBATA, Midori Kato, Akio Tsugeno,
... to detect the π-conjugative stabilization of bridgehead carbocations has been applied to eight 2-oxo (X = O) bridgehead carbocations. On the basis of the solvolytic behavior observed ... the π-conjugative stabilization of tertiary α-carbonyl carbocations is negligibly small, if present. Slightly more negative ... to complex conformations in the ground and incipient carbocations. PM3 calculations on some 2-methylene and 2-oxo bridgehead carbocations supported the experimental results. Comparison of the solvolysis ...
Tópico(s): Chemical Reactions and Mechanisms
1997 - American Chemical Society | The Journal of Organic Chemistry