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Search for "EPR" in Full Text gives 68 result(s) in Beilstein Journal of Organic Chemistry.

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition

  • Yulia V. Khoroshunova,
  • Denis A. Morozov,
  • Andrey I. Taratayko,
  • Polina D. Gladkikh,
  • Yuri I. Glazachev and
  • Igor A. Kirilyuk

Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200

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  • the range of 54–75%. Of note, the use of a similar three-step procedure for the synthesis of 1 from 19 increased the yield of this nitroxide from 20% [6] to 60% (Scheme 8). The EPR spectra of nitroxides 12a–c and 1 acquired in a deoxygenated buffer revealed a significant difference in line widths (see
  • Table 1 and Supporting Information File 1, Figures S7–S10), with the broadest lines expectedly being shown by 12b. Introduction of spirocyclohexane moieties to α-carbons of pyrrolidine nitroxides was found to cause strong broadening of lines in the EPR spectra, presumably owing to unresolved hfc on the
  • hydrogens at positions 2 and 6 of the cyclohexane ring [22]. It has been reported that EPR spectra of pyrrolidine or imidazolidine nitroxides with pair(s) of geminal ethyl groups at α-carbon atoms may feature large doublet hyperfine splittings [23][24][25]. For imidazolidine nitroxides, these splittings
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Published 27 Aug 2019

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells

  • Ayato Yamada,
  • Manabu Abe,
  • Yoshinobu Nishimura,
  • Shoji Ishizaka,
  • Masashi Namba,
  • Taku Nakashima,
  • Kiyofumi Shimoji and
  • Noboru Hattori

Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84

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  • addition to their ease of handling, nitroxides are highly sensitive to electron paramagnetic resonance (EPR) spectroscopy and redox reactions. Therefore, nitroxides have been developed and utilized in diverse and crucial applications, not only in chemistry, but also in biology, physiology, and energy
  • stable in benzene below 320 K (47 °C), as confirmed by electron paramagnetic resonance (EPR) spectroscopic analysis. Significant thermal decomposition of 2a and 2b was observed at ≈340 K (67 °C), as indicated by the typical EPR signals (see Supporting Information File 1, Figure S1). The photophysical
  • 365 nm light (6.02 × 1015 photons s−1) under atmospheric conditions (Figure 1). Clean release of the TEMPO radical was confirmed by measuring the electron paramagnetic resonance (EPR) signals of the typical nitroxide, AN = 15.5 G (g = 2.00232, Figure 1 and Figure 2c). The first-order rate constant for
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Published 10 Apr 2019
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  • intermediate IV. Finally, this intermediate is split by a nucleophilic attack of hydroxyl radicals to afford byproducts (including acetic acid, acetanilide, and formic acid) and desired product. The proposed mechanism was confirmed by EPR spectrum. The SSA catalyst is an inexpensive and reusable solid acid
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Published 01 Nov 2018

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

  • Hendrik V. Schröder and
  • Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

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  • -type arrangement in the dimer [34]. Furthermore, the equilibrium between a paramagnetic monomer and a diamagnetic dimer makes the use of electron paramagnetic resonance (EPR) spectroscopy ideal to follow the dimerization process [36]. Mixed-valence and radical-cation interactions in the solid state are
  • formed with a radical-cation dimer (10●+)2 stabilized in the cavity of the host molecule 9. The presence of the radical-cation dimer complex (10●+)29 was demonstrated by NMR, UV–vis and EPR spectroscopy. This was a novelty because stable TTF radical-cation dimers, which are usually only weakly associated
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Published 20 Aug 2018

Phosphoramidite building blocks with protected nitroxides for the synthesis of spin-labeled DNA and RNA

  • Timo Weinrich,
  • Eva A. Jaumann,
  • Ute M. Scheffer,
  • Thomas F. Prisner and
  • Michael W. Göbel

Beilstein J. Org. Chem. 2018, 14, 1563–1569, doi:10.3762/bjoc.14.133

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  • resulting spin-labeled palindromic duplexes could be directly investigated by PELDOR spectroscopy without further purification steps. Spin–spin distances measured by PELDOR correspond well to the values obtained from molecular models. Keywords: EPR; oligonucleotide; PELDOR; photolabile protection; TEMPO
  • ; Introduction EPR spectroscopy is well established to study the structure and dynamics of nucleic acids [1][2][3][4][5][6][7][8]. Although the information attainable by EPR is less detailed when compared to NMR, it is often complementary. While local conformations are normally obtained from NMR data, EPR can
  • hydroxylamines spontaneously reacted with air to form the nitroxide radicals in high yield [43]. Although the rigid spin labels introduced by Sigurdsson [31][32][33], Hopkins [27][29] and Engels [20][21] are generally considered advantageous for EPR studies, TEMPO-modified RNAs according to structures 1 and 3
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Published 26 Jun 2018

An unusual thionyl chloride-promoted C−C bond formation to obtain 4,4'-bipyrazolones

  • Gernot A. Eller,
  • Gytė Vilkauskaitė,
  • Algirdas Šačkus,
  • Vytas Martynaitis,
  • Ashenafi Damtew Mamuye,
  • Vittorio Pace and
  • Wolfgang Holzer

Beilstein J. Org. Chem. 2018, 14, 1287–1292, doi:10.3762/bjoc.14.110

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  • afforded the corresponding 2,2',4,4'-tetrahydro-3H,3'H-4,4'-bipyrazole-3,3'-dione, whereas it was shown by EPR spectroscopy and by cyclic voltammetry that the reaction obviously proceeds via a radical mechanism [32]. To the best of our knowledge, the only such dimeric species with ester functions at
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Published 04 Jun 2018

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

  • Satoru Mori and
  • Norio Shibata

Beilstein J. Org. Chem. 2017, 13, 2273–2296, doi:10.3762/bjoc.13.224

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  • accumulate in cancer cells due to the EPR (enhanced permeation and retention) effect [97][98]. This is a phenomenon in which new blood vessels around cancer cells allow macromolecules to pass easily through cells, causing the accumulation of molecules around cancer cells as a result. This effect is more
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Published 27 Oct 2017

Conformational study of L-methionine and L-cysteine derivatives through quantum chemical calculations and 3JHH coupling constant analyses

  • Weslley G. D. P. Silva,
  • Carolyne B. Braga and
  • Roberto Rittner

Beilstein J. Org. Chem. 2017, 13, 925–937, doi:10.3762/bjoc.13.94

Graphical Abstract
  • conformational equilibrium of the studied compounds. Frequency calculations with ZPE corrections were carried out to guarantee the absence of imaginary frequencies in the geometries. Spin-spin coupling constants (3JHH) were calculated for each conformer in the IEF−PCM model using the ωB97X-D functional and EPR
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Published 17 May 2017

Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

  • Stephen Hill and
  • M. Carmen Galan

Beilstein J. Org. Chem. 2017, 13, 675–693, doi:10.3762/bjoc.13.67

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  • red-shifted emission with increasing size. Moreover, the presence of defect sites, which are associated to the PL properties, is confirmed using room temperature electron paramagnetic resonance (EPR) spectroscopy, by the presence of free electrons in the spectra. Further functionalization of the
  • carboxylic acids that could be functionalised. Surface conjugation with PEG-diamine afforded a steric blocking, enhanced permeation and retention (EPR) shell, whilst providing an amine functionality for further surface conjugation. The anticancer drug methotrexate (MTX), which is a well-studied drug used to
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Published 10 Apr 2017

The reductive decyanation reaction: an overview and recent developments

  • Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

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  • NHC-boryl nitrile 74, EPR spectroscopy observations [122], and polar effects fit with this proposition. Neutral organic electron donors Powerful single-electron transfer reagents have been described. Kang et al. reported the decyanation of both malononitriles and α-cyanoesters using samarium(II
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Published 13 Feb 2017

Computational methods in drug discovery

  • Sumudu P. Leelananda and
  • Steffen Lindert

Beilstein J. Org. Chem. 2016, 12, 2694–2718, doi:10.3762/bjoc.12.267

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  • resonance (EPR) spectroscopy data has also been used in high-resolution de novo structure prediction [75][76][77]. Protein and small molecule databases Information about drug molecules and target structures is critical in using SBDD tools and many repositories collect and store such information about small
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Published 12 Dec 2016

Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

  • Nikolay O. Chalkov,
  • Vladimir K. Cherkasov,
  • Gleb A. Abakumov,
  • Andrey G. Starikov and
  • Viacheslav A. Kuropatov

Beilstein J. Org. Chem. 2016, 12, 2450–2456, doi:10.3762/bjoc.12.238

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  • protic solvents were studied by EPR spectroscopy. The formation of relatively stable paramagnetic protonated redox forms of the parent triad was very surprising. The character of spin-density distribution in the semiquinone–quinone and semiquinone–catechol redox forms indicates that the p-phenylene
  • ; EPR spectroscopy; extended tetrathiafulvalene; protonated semiquinone; Introduction The main idea that led to the creation of the system constructed of two o-quinone terminal moieties bridged with annulated extended tetrathiafulvalene (TTF) insertion, was an attempt to explore acceptor–donor–acceptor
  • drives electronic communication between paramagnetic centers at the termini. Coordination compounds and other derivatives containing the quinone-exTTF-quinone system in a paramagnetic state are numerous, and EPR spectroscopy seems best suited for the study of such objects. The coupling constants with
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Published 17 Nov 2016

One-pot synthesis of 4′-alkyl-4-cyanobiaryls on the basis of the terephthalonitrile dianion and neutral aromatic nitrile cross-coupling

  • Roman Yu. Peshkov,
  • Elena V. Panteleeva,
  • Wang Chunyan,
  • Evgeny V. Tretyakov and
  • Vitalij D. Shteingarts

Beilstein J. Org. Chem. 2016, 12, 1577–1584, doi:10.3762/bjoc.12.153

Graphical Abstract
  • being used as components of liquid crystal mixtures [3][4][5][6][7][8], lubricants [9], media for conformational analysis using NMR [10][11][12] and EPR [13] techniques, and nanoparticles-doped liquid crystals [14]. The classic multistage approaches to these compounds, including successive biphenyl
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Published 25 Jul 2016

Recent developments in copper-catalyzed radical alkylations of electron-rich π-systems

  • Kirk W. Shimkin and
  • Donald A. Watson

Beilstein J. Org. Chem. 2015, 11, 2278–2288, doi:10.3762/bjoc.11.248

Graphical Abstract
  • synthesized in very good yields (Scheme 16). Interestingly, the CuCl/phenanthroline catalyst system was also capable of cross coupling styrenes with α-bromocarbonyls and α-bromonitriles. EPR studies confirmed the presence of radical intermediates. Additions to alkynes Recently, ATR type catalysts have also
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Published 23 Nov 2015

Recent advances in copper-catalyzed C–H bond amidation

  • Jie-Ping Wan and
  • Yanfeng Jing

Beilstein J. Org. Chem. 2015, 11, 2209–2222, doi:10.3762/bjoc.11.240

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  • donor to provide a methyl radical as the precursor of the methyl cation which was crucial for the subsequent annulation. The radical process of the reaction was also supported by the EPR experiment (Scheme 25). While most of the known C–H amidation-based cascade reactions afforded six-membered or
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Published 17 Nov 2015

Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst

  • Redouane Beniazza,
  • Natalia Bayo,
  • Florian Molton,
  • Carole Duboc,
  • Stéphane Massip,
  • Nathan McClenaghan,
  • Dominique Lastécouères and
  • Jean-Marc Vincent

Beilstein J. Org. Chem. 2015, 11, 1950–1959, doi:10.3762/bjoc.11.211

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  • mercury lamp (type TLC = thin-layer chromatography, 365 nm), or by a 23 W fluorescent bulb, or by ambient/sunlight. In water, a much poorer hydrogen atom donating solvent, the photoreduction of 1 proved inefficient. Interestingly, EPR studies revealed that complex 1 could nonetheless be effectively
  • (Scheme 3), precluded the use of UV–vis spectroscopy to quantitatively analyze the reductive process. For such an analysis, EPR spectroscopy was thus employed to assess the extent of copper reduction. In Figure 3, the EPR spectra of solutions of 1 (d9, S = 1/2) recorded by irradiating the samples directly
  • in the probe at room temperature are presented. Control experiments conducted in THF and aqueous solutions of 1 (Figure 3a and b, respectively), confirmed the results gathered by UV–vis spectroscopy, i.e., fast reduction in THF and essentially no reduction in water. In water solution, the EPR spectra
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Published 21 Oct 2015

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

  • David W. Manley and
  • John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

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  • -carboxylic acid, was isolated and characterized. That the derived C-centered radicals R• were intermediates was implied by EPR detection of Ph3C• (from Ph3CCO2H) and the PBN spin adduct of CH3• radicals from acetic acid [38]. The first successful applications of SCPC to the formation of novel organic
  • valence band holes [61]. Electron transfer from the carboxylate π-orbitals to a hole trap site supplies surface bound RXCH2-CO2• radicals. Rapid β-scissions of these species yield the desired free RXCH2• radicals. That these species are intermediates has been confirmed by detection of their EPR spectra in
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Published 09 Sep 2015

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

  • Huixin Jiang,
  • Virginia Mazzanti,
  • Christian R. Parker,
  • Søren Lindbæk Broman,
  • Jens Heide Wallberg,
  • Karol Lušpai,
  • Adam Brincko,
  • Henrik G. Kjaergaard,
  • Anders Kadziola,
  • Peter Rapta,
  • Ole Hammerich and
  • Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

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  • were investigated by cyclic voltammetry, UV–vis–NIR and EPR absorption spectroscopical methods of the electrochemically generated oxidized species. The electron-accepting properties of the acetylenic cores were also investigated electrochemically. Keywords: alkynes; mixed valence; radiaannulene
  • low energy (2257 nm). We became interested in elucidating the dependence on acyclic versus cyclic bridging units in more detail by cyclic voltammetry and EPR/UV–vis–NIR spectroelectrochemistry. With regard to conformational flexibility and the lack of it, it deserves mentioning that Low and co-workers
  • acyclic components, 1a and 5 (−1.65 V and −2.35 V vs Fc/Fc+). UV–vis–NIR and EPR spectra of oxidized species The EPR and optical (UV–vis–NIR) properties of the oxidized species were studied by in situ spectroelectrochemistry in CH2Cl2 (Bu4NPF6) at a platinum mesh electrode. Even at low scan rate of 2 mV s
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Published 02 Jun 2015

IR and electrochemical synthesis and characterization of thin films of PEDOT grown on platinum single crystal electrodes in [EMMIM]Tf2N ionic liquid

  • Andrea P. Sandoval,
  • Marco F. Suárez-Herrera and
  • Juan M. Feliu

Beilstein J. Org. Chem. 2015, 11, 348–357, doi:10.3762/bjoc.11.40

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  • ) increases between −0.3 V and −0.1 V where a plateau is reached. This IR signal also behaves very similar as the EPR signal intensity upon changing potential reported by Domagala et al. [23]. Finally, it is important to remember that when a weak electric field is applied across a molecule, both the molecular
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Published 13 Mar 2015

TEMPO-derived spin labels linked to the nucleobases adenine and cytosine for probing local structural perturbations in DNA by EPR spectroscopy

  • Dnyaneshwar B. Gophane and
  • Snorri Th. Sigurdsson

Beilstein J. Org. Chem. 2015, 11, 219–227, doi:10.3762/bjoc.11.24

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  • being the least mobile. Furthermore, TA showed decreased mobility under acidic conditions for the sequences TA•C and TA•G, to the extent that the EPR spectrum of the latter became nearly superimposable to that of TA•T. The reduced mobility of the TA•C and TA•G mismatches at pH 5 is consistent with the
  • formation of TAH+•C and TAH+•G, in which protonation of N1 of A allows the formation of an additional hydrogen bond to N3 of C and N7 of G, respectively, with G in a syn-conformation. The urea-based spin labels UA and UC were more mobile than TA, but still showed a minor variation in their EPR spectra when
  • can be obtained by X-ray crystallography [1][2][3][4][5][6] and nuclear magnetic resonance (NMR) spectroscopy [7][8][9][10][11][12]. Electron paramagnetic resonance (EPR) and fluorescence spectroscopies are nowadays routinely used to study global structures and conformational changes under
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Published 09 Feb 2015

Formulation development, stability and anticancer efficacy of core-shell cyclodextrin nanocapsules for oral chemotherapy with camptothecin

  • Hale Ünal,
  • Naile Öztürk and
  • Erem Bilensoy

Beilstein J. Org. Chem. 2015, 11, 204–212, doi:10.3762/bjoc.11.22

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  • enhanced permeation retention effect (EPR) [3]. In vitro release of CPT from both anionic and cationic nanocapsules were performed in phosphate buffered saline (PBS) medium at pH 7.4 and at pH 1.2 to mimic the conditions inside the body representing blood and stomach, respectively (see Supporting
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Published 04 Feb 2015

Preparation and evaluation of cyclodextrin polypseudorotaxane with PEGylated liposome as a sustained release drug carrier

  • Kayoko Hayashida,
  • Taishi Higashi,
  • Daichi Kono,
  • Keiichi Motoyama,
  • Koki Wada and
  • Hidetoshi Arima

Beilstein J. Org. Chem. 2014, 10, 2756–2764, doi:10.3762/bjoc.10.292

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  • and forms a hydrophilic layer on the surface of LPs [28]. It is not recognized by RES, which leads to a prolonged retention in circulation (stealth characteristics), and shows the enhanced permeability retention (EPR) effect [36]. PEG-LP is widely used as a drug carrier to realize the targeted drug
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Published 25 Nov 2014

Automated solid-phase peptide synthesis to obtain therapeutic peptides

  • Veronika Mäde,
  • Sylvia Els-Heindl and
  • Annette G. Beck-Sickinger

Beilstein J. Org. Chem. 2014, 10, 1197–1212, doi:10.3762/bjoc.10.118

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  • during SPPS allowing EPR (electron paramagnetic resonance) studies to investigate conformational changes during receptor binding [129]. Here, synthesis on solid support could be easily realized. Nevertheless, conditions for cleavage of the peptide conjugates from the resin had to be optimized owing to
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Published 22 May 2014

A new building block for DNA network formation by self-assembly and polymerase chain reaction

  • Holger Bußkamp,
  • Sascha Keller,
  • Marta Robotta,
  • Malte Drescher and
  • Andreas Marx

Beilstein J. Org. Chem. 2014, 10, 1037–1046, doi:10.3762/bjoc.10.104

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  • DNA and branched DNA networks, gave the possibility to conclude that DNA networks existed in solution in variable shapes. Next we employed electron paramagnetic resonance (EPR) spectroscopy for investigation of the DNA networks. EPR is a widespread technique for the studies of structural and dynamic
  • properties of biological macromolecules, e.g., DNA [48][49][50][51][52][53]. Since the systems studied in the current investigation are diamagnetic, nitroxide labels had to be inserted enzymatically [54][55]. EPR spectra of nitroxide labels are sensitive to dynamics on the picosecond to microsecond
  • conformational changes compared to the rest of the macromolecule. As the EPR-signal arises from these three processes, the interpretation of EPR spectra is rendered difficult. Measurements at a single frequency do not allow complete description of the spin label motion. However, a spectrum often can be
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Published 07 May 2014

Conformational analysis of 2,2-difluoroethylamine hydrochloride: double gauche effect

  • Josué M. Silla,
  • Claudimar J. Duarte,
  • Rodrigo A. Cormanich,
  • Roberto Rittner and
  • Matheus P. Freitas

Beilstein J. Org. Chem. 2014, 10, 877–882, doi:10.3762/bjoc.10.84

Graphical Abstract
  • ] analyses were also performed at the B3LYP/6-311++g(d,p) level of theory [19][22][23], including deletion of all antibonding and Rydberg-type orbitals. Spin–spin coupling constants were calculated at the BHandH/EPR-III level [24][25]. All these calculations were carried out using the Gaussian 09 program [26
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Published 16 Apr 2014
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