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Search for "quantum chemical calculations" in Full Text gives 98 result(s) in Beilstein Journal of Organic Chemistry.

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

  • Christian Muschelknautz,
  • Robin Visse,
  • Jan Nordmann and
  • Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 599–612, doi:10.3762/bjoc.10.51

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  • quantum chemical calculations on the DFT level (B3LYP functional, 6-31G* basis set) [40]. The computed Kohn–Sham frontier molecular orbitals of compound 8a clearly indicate a charge transfer from the aminovinyl dominated donor fragment in the HOMO to the indolone-centered LUMO, which is generally
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Published 05 Mar 2014

Decandrinin, an unprecedented C9-spiro-fused 7,8-seco-ent-abietane from the Godavari mangrove Ceriops decandra

  • Hui Wang,
  • Min-Yi Li,
  • Félix Zongwe Katele,
  • Tirumani Satyanandamurty,
  • Jun Wu and
  • Gerhard Bringmann

Beilstein J. Org. Chem. 2014, 10, 276–281, doi:10.3762/bjoc.10.23

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  • combination with quantum-chemical calculations. Decandrinin is the first 7,8-seco-ent-abietane. Keywords: abietane; absolute configuration; Ceriops decandra; circular dichroism; decandrinin; Rhizophoraceae; Introduction Ceriops decandra is a mangrove of the family Rhizophoraceae. It is widely distributed
  • NMR investigations, and by circular dichroism (CD) and optical-rotatory dispersion (ORD) spectroscopy in combination with quantum-chemical calculations. Results and Discussion Decandrinin (1) was obtained as a colorless solid. Its molecular formula was established as C20H28O4 by HRMS (ESI) (m/z
  • because there would be several atoms between the concerned protons (Figure S9 in Supporting Information File 1). Therefore, the relative configuration of 1 was identified as shown in Figure 1. The absolute configuration of 1 was assigned by CD and ORD spectroscopy in combination with quantum-chemical
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Published 27 Jan 2014

New hydrogen-bonding organocatalysts: Chiral cyclophosphazanes and phosphorus amides as catalysts for asymmetric Michael additions

  • Helge Klare,
  • Jörg M. Neudörfl and
  • Bernd Goldfuss

Beilstein J. Org. Chem. 2014, 10, 224–236, doi:10.3762/bjoc.10.18

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  • and the OMG group for generous support. We would also like to thank Dr. Nils Schlörer for the NMR measurements, Dr. Matthias Leven for competent advice on quantum chemical calculations and Dipl. Chem. Falco Fox for the preparation of precursors. We thank the RRZK Cologne for computing time.
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Published 21 Jan 2014

Less reactive dipoles of diazodicarbonyl compounds in reaction with cycloaliphatic thioketones – First evidence for the 1,3-oxathiole–thiocarbonyl ylide interconversion

  • Valerij A. Nikolaev,
  • Alexey V. Ivanov,
  • Ludmila L. Rodina and
  • Grzegorz Mlostoń

Beilstein J. Org. Chem. 2013, 9, 2751–2761, doi:10.3762/bjoc.9.309

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  • . Victor Baranovski and Dr. Andrey Mereshchenko (St. Petersburg State University) for their help in quantum chemical calculations, and Prof. Anthony Linden (University of Zurich) for the X-ray analysis of 1,3-dithiolane 3a. Skillful help by Dr. K. Urbaniak and Mrs. Małgorzata Celeda in the preparation of
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Published 02 Dec 2013

Thermochemistry and photochemistry of spiroketals derived from indan-2-one: Stepwise processes versus coarctate fragmentations

  • Götz Bucher,
  • Gernot Heitmann and
  • Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1668–1676, doi:10.3762/bjoc.9.191

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  • useful, but suitable to check the coarctate stereochemical rules, is a peculiar fragmentation reaction that we discovered 15 years ago (Scheme 1) [9][10]. The reaction proceeds spontaneously at temperatures below −80 °C. Quantum chemical calculations of the parent reaction predict an activation barrier
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Published 15 Aug 2013

Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

  • Andreas Gansäuer,
  • Meriam Seddiqzai,
  • Tobias Dahmen,
  • Rebecca Sure and
  • Stefan Grimme

Beilstein J. Org. Chem. 2013, 9, 1620–1629, doi:10.3762/bjoc.9.185

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  • enthalpies and relative values for different compounds (trends) should have an error <1 kcal mol−1. Results and Discussion Theoretical methods and benchmarking Computational details The quantum chemical calculations have been performed with the TURBOMOLE 6.4 suite of programs [34]. All geometry optimizations
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Published 08 Aug 2013

Host–guest complexes of mixed glycol-bipyridine cryptands: prediction of ion selectivity by quantum chemical calculations, part V

  • Svetlana Begel,
  • Ralph Puchta and
  • Rudi van Eldik

Beilstein J. Org. Chem. 2013, 9, 1252–1268, doi:10.3762/bjoc.9.142

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  • , nondynamic quantum chemical calculations, performed in the absence of solvent molecules and focusing on the system itself, were utilized very successfully for the careful examination of the supramolecules, excluding possible disturbing side effects. The current work extends our explorations into the outlined
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Published 27 Jun 2013

Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

  • Jianhuai Ye,
  • Yoshihisa Fujiwara and
  • Manabu Abe

Beilstein J. Org. Chem. 2013, 9, 925–933, doi:10.3762/bjoc.9.106

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  • categorized as Type-1 diradicals [1][27], which possess a π-single-bonding character (–π–, closed-shell character) between the two radical sites. The role of the alkoxy group (OR) on the lifetime (k = 1/τ) was investigated by combined studies of experiments and quantum chemical calculations [26][28]. The
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Published 14 May 2013

Synthesis, photophysical and electrochemical characterization of terpyridine-functionalized dendritic oligothiophenes and their Ru(II) complexes

  • Amaresh Mishra,
  • Elena Mena-Osteritz and
  • Peter Bäuerle

Beilstein J. Org. Chem. 2013, 9, 866–876, doi:10.3762/bjoc.9.100

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  • nonemissive [Ru(tpy)2]2+ center of the metallodendrimer. Quantum chemical calculations. In order to gain insight into the structural properties, the electron density distribution of the frontier orbitals of both complexes was analyzed by density functional theory (DFT) using the B3LYP/LANL2DZ basis set
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Published 06 May 2013

Direct alkenylation of indolin-2-ones by 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles: a novel approach

  • Sandeep Kumar,
  • Ramendra Pratap,
  • Abhinav Kumar,
  • Brijesh Kumar,
  • Vishnu K. Tandon and
  • Vishnu Ji Ram

Beilstein J. Org. Chem. 2013, 9, 809–817, doi:10.3762/bjoc.9.92

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  • desired product. NaH in THF was found to be the most suitable for the alkenylation of indolin-2-ones. Reaction in the presence of other bases led to the formation of 1-aryl-3-methoxy/methylthio-5H-dibenzo[d,f][1,3]diazepin-6(7H)-ones. Quantum chemical calculations have been performed to explain the nature
  • isolated compound. Single-crystal X-ray studies revealed that out of the three tautomeric forms, the 8y is the most suitable structure based on the bond lengths. Quantum chemical calculations have been performed in order to gain information regarding the relative energy difference, which in turn reflects
  • -oxindoles. Furthermore, the synthesis of 8y and its relative stability with respect to the other tautomers has been confirmed by single-crystal X-ray analysis and quantum chemical calculations. X-ray diffraction displayed various C−H…π, C−H…O and Ar-H…π intermolecular interactions. These interactions have
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Published 25 Apr 2013

Caryolene-forming carbocation rearrangements

  • Quynh Nhu N. Nguyen and
  • Dean J. Tantillo

Beilstein J. Org. Chem. 2013, 9, 323–331, doi:10.3762/bjoc.9.37

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  • about putting this proposal to the test using quantum chemical calculations [8]. Results and Discussion Structure validation: We first computed 1H and 13C chemical shifts for 1 to assure ourselves that the assigned structure was reasonable [9][10]. Our calculated chemical shifts and the reported data
  • biosynthetic precursor to 1. Despite the apparent reasonability of this proposed mechanism, our quantum chemical calculations indicated that the pathway as formulated in Scheme 1 is not energetically viable (see below). Computed mechanism: The first deviation from the proposed mechanism in Scheme 1 was
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Published 13 Feb 2013

Metal-mediated aminocatalysis provides mild conditions: Enantioselective Michael addition mediated by primary amino catalysts and alkali-metal ions

  • Matthias Leven,
  • Jörg M. Neudörfl and
  • Bernd Goldfuss

Beilstein J. Org. Chem. 2013, 9, 155–165, doi:10.3762/bjoc.9.18

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  • crystallographic data for compound 5. Acknowledgements We thank Eduard Maibach from the Merholz group for performing ESIMS measurements and evaluation of related data. We thank Lars Packschies and the RRZK for providing well furnished HPC systems for efficient quantum chemical calculations. We are grateful to the
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Published 23 Jan 2013

The chemistry of bisallenes

  • Henning Hopf and
  • Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

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Published 15 Nov 2012

Synthesis and evaluation of new guanidine-thiourea organocatalyst for the nitro-Michael reaction: Theoretical studies on mechanism and enantioselectivity

  • Tatyana E. Shubina,
  • Matthias Freund,
  • Sebastian Schenker,
  • Timothy Clark and
  • Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2012, 8, 1485–1498, doi:10.3762/bjoc.8.168

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  • -chemical calculations on the mechanism and the observed stereoselectivity. Results and Discussion Synthesis and application of new guanidine-thiourea catalyst 7 The syntheses of new guanidine-thiourea compound 7 was accomplished by known methods [36][38][40][54][55][56] as summarised in Scheme 1. (S,S)-1,2
  • -thiourea organocatalyst has been published up until now [50][51][52][53]. This encouraged us to synthesize and investigate the potential of new guanidine-thiourea 7 as organocatalyst for the nitro-Michael addition reactions. Here we report the first results of our investigations, accompanied by quantum
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Published 07 Sep 2012

A quantitative approach to nucleophilic organocatalysis

  • Herbert Mayr,
  • Sami Lakhdar,
  • Biplab Maji and
  • Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

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  • by quantum chemical calculations: The methyl cation affinities (MCAs) of the three carbenes 41–43 are 100–200 kJ mol–1 higher than those of the other Lewis bases in Figure 23 [96]. As the carbenes 41 and 42 have almost identical nucleophilicities and Lewis basicities, the question arose as to why
  • different behavior was analyzed by quantum chemical calculations (Figure 25b). In the same way that the nucleophilicity order of the carbenes (41 ≈ 42 > 43, Figure 23) parallels the order of the Lewis basicities (methyl cation affinities) of the model compounds (49c ≈ 49a > 49b, Figure 25b bottom), the
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Published 05 Sep 2012

Conformational analysis, stereoelectronic interactions and NMR properties of 2-fluorobicyclo[2.2.1]heptan-7-ols

  • Fátima M. P. de Rezende,
  • Marilua A. Moreira,
  • Rodrigo A. Cormanich and
  • Matheus P. Freitas

Beilstein J. Org. Chem. 2012, 8, 1227–1232, doi:10.3762/bjoc.8.137

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  • .8.137 Abstract Four diastereoisomers of 2-fluorobicyclo[2.2.1]heptan-7-ols were computationally investigated by using quantum-chemical calculations, and their relative energies were analyzed on the basis of stereoelectronic interactions, particularly the presence or otherwise of the F∙∙∙HO
  • bond. Keywords: conformational analysis; 2-fluorobicyclo[2.2.1]heptan-7-ols; hydrogen bond; 1hJF,H(O) coupling constant; quantum-chemical calculations; Introduction Intra- and intermolecular hydrogen bonds (HB) play an important role in determining the molecular arrangements and properties, as well
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Published 02 Aug 2012

Control over molecular motion using the cistrans photoisomerization of the azo group

  • Estíbaliz Merino and
  • María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

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  • molecular motion similar to a hinge, in which the two aromatic rings are arranged at an angle of 90°. The photoisomerization process involves three isomeric forms: (trans,trans), (trans,cis) and (cis,cis). The heats of formation of the three isomers were determined by ab initio quantum chemical calculations
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Published 12 Jul 2012

Toward unidirectional switches: 2-(2-Hydroxyphenyl)pyridine and 2-(2-methoxyphenyl)pyridine derivatives as pH-triggered pivots

  • Christina Tepper and
  • Gebhard Haberhauer

Beilstein J. Org. Chem. 2012, 8, 977–985, doi:10.3762/bjoc.8.110

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  • was investigated with the help of UV spectroscopy. Quantum chemical calculations at the B3LYP/6-31G* level of theory were performed to show that in the case of 2-(2-methoxyphenyl)-3-methylpyridine and 2-(2-hydroxyphenyl)-3-methylpyridine the rotation during the switching process proceeds
  • unidirectional rotation process caused by protonation, the methyl derivatives of 1–4, i.e., 5–8 (Scheme 2) were investigated by using quantum chemical calculations at the B3LYP/6-31G* level of theory. Due to the methyl group, all conformations with a dihedral angle θN–C–C–C(O) of 180° represent energy maxima
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Published 29 Jun 2012

Synthesis, solid-state fluorescence properties, and computational analysis of novel 2-aminobenzo[4,5]thieno[3,2-d]pyrimidine 5,5-dioxides

  • Kenichirou Yokota,
  • Masayori Hagimori,
  • Naoko Mizuyama,
  • Yasuhisa Nishimura,
  • Hiroshi Fujito,
  • Yasuhiro Shigemitsu and
  • Yoshinori Tominaga

Beilstein J. Org. Chem. 2012, 8, 266–274, doi:10.3762/bjoc.8.28

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  • reproduced by a series of ab initio quantum-chemical calculations. Keywords: amino group; fluorescence; HOMO/LUMO; pyrimidine; solid-state; Introduction Solid-state fluorescent compounds are currently attracting considerable interest from both theoretical and practical standpoints [1][2][3][4]. Recently
  • pyrimidine derivatives. It is thought that these derivatives show strong fluorescence as a result of the presence of a hetero-π-electron conjugated system [7]. The electronic and emission spectra of these new compounds were analyzed computationally by using a series of ab initio quantum-chemical calculations
  • initio quantum-chemical calculations. The theoretical analyses quantitatively reproduced the S0→S1 and S1→S0 transitions. The associated HOMO/LUMO distributions and the transition characters were also elucidated theoretically. Experimental General Identifications of compounds and measurements of
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Published 16 Feb 2012

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

  • Jiří Kulhánek and
  • Filip Bureš

Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4

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  • ]). These chromophores were synthesized by Debus–Radziszewski synthesis (Scheme 1), as two series of compounds with different acceptors A (NO2 or CN groups), and were investigated by electrochemistry, UV–vis and IR spectroscopy (CN), and quantum-chemical calculations (Table 5). Considering all the above
  • were primarily investigated by electronic-absorption spectra, electrochemistry, X-ray analysis, and quantum-chemical calculations. The resulting data set was further processed by factor analysis to deduce the structure–property relationships. The most important structural factors affecting the (non
  • within the studied series. The photoinduced absorption, birefringence, and second-harmonic generation of chromophores 88c–93c (D = NMe2) embedded within polymethylmethacrylate matrices were studied and complimented by quantum-chemical calculations. These doped polymer films showed very efficient and
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Published 05 Jan 2012

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

  • Leping Liu,
  • Bo Xu and
  • Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

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  • transfer of 2-alkynyl-1,5-diketones. The discovery of a [4 + 2] cycloaddition of a furanium intermediate to a carbonyl group was further verified by quantum chemical calculations. The competing [2 + 2] and [4 + 2] reaction coordinates were computed for the simplified substrate 11a, shown in Scheme 10. In
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Published 13 May 2011

Syntheses and properties of thienyl-substituted dithienophenazines

  • Annemarie Meyer,
  • Eva Sigmund,
  • Friedhelm Luppertz,
  • Gregor Schnakenburg,
  • Immanuel Gadaczek,
  • Thomas Bredow,
  • Stefan-S. Jester and
  • Sigurd Höger

Beilstein J. Org. Chem. 2010, 6, 1180–1187, doi:10.3762/bjoc.6.135

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  • -condensed thiophene analogues. These assignments of the thiophene moieties as donors and the phenazine moieties as acceptors are confirmed by quantum-chemical calculations at the density-functional level. Additionally, one of the compounds forms a self-assembled monolayer on a HOPG surface, as imaged by
  • , when compared with the optical spectra of the quater- and sexithiophene [28] (Table 2, 19 and 20), a clear red-shift could be observed for both oligomer series, regardless if they are based on 10 or 11, due to the intramolecular donor-acceptor character of the compounds. Quantum chemical calculations
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Published 13 Dec 2010

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

  • Giorgio Bencivenni,
  • Riccardo Cesari,
  • Daniele Nanni,
  • Hassane El Mkami and
  • John C. Walton

Beilstein J. Org. Chem. 2010, 6, 713–725, doi:10.3762/bjoc.6.84

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  • explain the absence of the 19F high-frequency line in our spectrum. DFT computations of radical cation properties Quantum chemical calculations were carried out with the Gaussian 03 programme package [35][36]. Density functional theory with the UB3LYP functional was employed. The equilibrium geometries
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Published 09 Aug 2010
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