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Search for "quantum-chemical calculations" in Full Text gives 98 result(s) in Beilstein Journal of Organic Chemistry.
Muyocopronones A and B: azaphilones from the endophytic fungus Muyocopron laterale
Beilstein J. Org. Chem. 2020, 16, 2100–2107, doi:10.3762/bjoc.16.177
- experimental ECD spectra to elucidate the absolute configuration. In the quantum-chemical calculations, the generation of an excessive number of conformers was avoided using a molecular model in which the β-hydroxycarboxylic acid side chain at the C-7 position was simplified to an acetyloxy group (Figure 4A
One-pot synthesis of oxazolidinones and five-membered cyclic carbonates from epoxides and chlorosulfonyl isocyanate: theoretical evidence for an asynchronous concerted pathway
Beilstein J. Org. Chem. 2020, 16, 1805–1819, doi:10.3762/bjoc.16.148
- computational studies, such reactions of isocyanates may proceed through a concerted pathway. The remaining uncertainties in the mechanisms of the similar reactions inspired us to carry out quantum chemical calculations for the formation of oxazolidinone and five-membered cyclic carbonates. Results and
Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study
Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136
- ), respectively, was also investigated by DFT level quantum chemical calculations with the same parameters as in the case of the 1→2 rearrangement. The racemic RS and RR forms were taken into consideration, and the computations showed that the formation of the RS compound required an energy investment of ΔG#4e
Oxime radicals: generation, properties and application in organic synthesis
Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107
- example, based on N-containing heterocycles (isoxazolones, pyrazolones, pyrazolidin-3,5-diones, and 1,2,3-triazolones [52]), sulfones [65], and phosphonates [54] (Scheme 8). Based on the data of EPR spectroscopy [35][38][49][50][66] and quantum chemical calculations [67], the maximum spin density in
- isomers (E and Z) exist. The isomerization of oxime radicals proceeds much easier than for the corresponding oximes; the observation of individual isomers is generally possible only at low temperatures [68][69] (about 190 K). According to quantum chemical calculations, the oxime radicals have an increased
The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts
Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99
- providing supercomputer facilities. Funding The X-ray diffraction data were collected with financial support from the Ministry of Science and Higher Education of the Russian Federation using the equipment of the Center for Molecular Composition Studies of INEOS RAS. Quantum chemical calculations were
Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides
Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75
- double bond migration pathways were elucidated by quantum chemical calculations. Keywords: chlorophosphonium salts; isomerization; 2-phospholene oxides; 3-phospholene oxides; quantum chemistry; Introduction P-Heterocyclic derivatives are valuable targets in synthetic organophosphorus chemistry [1][2][3
- chemical calculations at MP2/6-31++G(d,p) and MP2/6-311++G(2d,2p) levels of theory, including the PCM solvent model with the parameters of THF. For these investigations, the 1-phenyl or 1-ethyl-3-methylphospholene oxides (1a or 1h) were considered as model compounds, but phospholene oxides incorporating
- isomerization remained incomplete under these conditions. It was found that methyl group(s) at positon 3 or 4 in the P-heterocyclic ring hinder the isomerization in all reaction pathways investigated. The mechanisms of acid- or base-mediated, as well as thermal isomerizations were elucidated by quantum chemical
Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0
Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40
- withdrawing moieties. Quantum chemical calculations showed only small contributions of the substituent placed at the meso-position to the electron density in the HOMO/LUMO pattern [81]. Presumably, coupling of lower occupied molecular orbitals with the HOMO on the one hand side and higher unoccupied MOs with
The reaction of arylmethyl isocyanides and arylmethylamines with xanthate esters: a facile and unexpected synthesis of carbamothioates
Beilstein J. Org. Chem. 2020, 16, 159–167, doi:10.3762/bjoc.16.18
- reactions, a mechanism is proposed in which the key steps are supported by quantum chemical calculations. Keywords: benzylamines; carbamothioates; density functional theory; intrinsic reaction coordinate analysis; isocyanides; sodium hydride; xanthate esters; Introduction Carbamothioates (thiocarbamates
- hypothesis. Computational studies on the proposed reaction mechanism Several possible reaction mechanisms were considered to account for the unexpected products obtained. Ultimately, we employed quantum chemical calculations to shed light on the most probable reaction pathway for the observed products, as
- simplify the quantum chemical calculations, the reactions shown in Scheme 2 involve a hydride as the nucleophile or base [34], although it is possible that dimethylamide, formed from the reaction of sodium hydride with DMF [35], could be the initiating nucleophile/base. All computations were carried out
Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?
Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290
- quantum-chemical calculations employing long-range corrected hybrid density ωB97X-D functional [42]. This dispersion-corrected functional displays very balanced overall performances and has demonstrated excellent treatment of noncovalent interactions [43], which are very important in our studied system
Azologization and repurposing of a hetero-stilbene-based kinase inhibitor: towards the design of photoswitchable sirtuin inhibitors
Beilstein J. Org. Chem. 2019, 15, 2170–2183, doi:10.3762/bjoc.15.214
- ortho methyl groups in 2f, intramolecular photocyclization could be prevented. To verify the hypothetical structures derived from irradiation of 2b, we carried out quantum chemical calculations of the double bond isomers (E)-2b and (Z)-2b as well as the oxidized compounds 8a and 8b. We used density
Tautomerism as primary signaling mechanism in metal sensing: the case of amide group
Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185
- 5. The quantum-chemical calculations for 4 and 5 have demonstrated that the stable enol tautomers exist as intramolecular C=O···HO bonded system, while in the K forms the ionophore part does not participate in hydrogen bonding and can be considered as a basic 2-alkyl substitution [9]. Consequently
- still not appear even after 1024 scans. Theoretical calculations Quantum-chemical calculations were performed using the Gaussian 09 D.01 program suite [17]. The M06-2X functional [18][19] was used with the 6-31++G** basis set for the calculations. This fitted hybrid meta-GGA functional with 54% HF
An azobenzene container showing a definite folding – synthesis and structural investigation
Beilstein J. Org. Chem. 2019, 15, 1534–1544, doi:10.3762/bjoc.15.156
- , whereas by the use of visible light the stretched trans,trans-isomer is formed. By means of quantum chemical calculations and CD spectroscopy we could show that the trans→cis isomerization is spatially directed; that means that one of the two different macrocycles performs a definite clockwise rotation to
- the other, caused by irradiation with UV light. For the cis→trans isomerization counterclockwise rotations are found. Furthermore, quantum chemical calculations reveal that the energy of the cis,cis-isomer is only slightly higher than the energy of the cis,trans-isomer. This effect can be explained by
- -containing macrocycles and the azobenzene bridges having two reactive bromides. The desired container could be isolated in a fair yield taking the multiple reaction pathways into account. Subsequent investigations by means of quantum chemical calculations, UV, CD and NMR spectroscopy revealed that the
Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction
Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138
- heterotriacenes 1 and 3 rationalize their unexpected higher melting point compared to 2 and 4. Quantum chemical calculations Quantum chemical DFT and TDDFT calculations (CAMB3LYP and B3LYP with the functional 6-31G++ (d,p)) were performed for the ground and excited state of heterotriacenes 1–4 in order to
- well soluble systems, which allowed for the determination of thermal, optical, and electrochemical properties. By single crystal X-ray structure analysis the geometric structure and packing motifs of selenolotriacenes 2–4 were determined. Quantum chemical calculations allowed for a deeper understanding
- conducted in reflectance mode. During recording the UV–vis–NIR spectra, the applied potential was kept constant. Instrumental artefacts due to the change of the detector were removed and marked in the spectra. Quantum chemical calculations were performed with the Gaussian 09 package: DFT and TDDFT with the
Synthesis of dipolar molecular rotors as linkers for metal-organic frameworks
Beilstein J. Org. Chem. 2019, 15, 1331–1338, doi:10.3762/bjoc.15.132
- be a completely unrealistic endeavour. Here we report on the synthesis of five different dipolar rotors (Figure 2) that are designed to meet the criteria 1–4 listed above, for the use as building blocks in the construction of functional MOFs. Results and Discussion Linker design and quantum chemical
- calculations Aiming at high dipole moments our design was inspired by recent reports of Müllen et al. who reported on very high dipole moments of 1,2-dicyano-4,5-diamino-substituted phenyl derivatives [35]. Unfortunately, amino substituents are not compatible with MOF growth. Cyano substituents could
Phylogenomic analyses and distribution of terpene synthases among Streptomyces
Beilstein J. Org. Chem. 2019, 15, 1181–1193, doi:10.3762/bjoc.15.115
- ionisation of the substrate FPP and the formation of a humulyl cation as an intermediate in the biosynthesis of pentalenene [45][46][48][49], while the later steps of the cyclisation cascade were subject to revision based on the findings of quantum chemical calculations [50][51]. The α-amorphene synthase
Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines
Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41
- with a possible character of TICT [55], which could explain a dual-fluorescence and fluorescence quenching in the high polarity media. The charge transfer nature of the transitions for the compounds 8c and 11c, compared to reference compounds 8a and 11a, was confirmed by quantum chemical calculations
- , 46.9, 55.3, 99.5, 101.6, 114.3, 116.2, 123.1, 126.7, 127.3, 146.7, 147.0, 156.6, 156.8, 159.8; HRMS–ESI (m/z): [M + H]+ calcd for C20H22N7O, 376.1880; found, 376.1887. Quantum chemical calculations The initial molecular geometries were generated by using a molecular mechanics method (force field MMF94
Computational characterization of enzyme-bound thiamin diphosphate reveals a surprisingly stable tricyclic state: implications for catalysis
Beilstein J. Org. Chem. 2019, 15, 145–159, doi:10.3762/bjoc.15.15
- . Keywords: binding site; DFT; enzyme mechanism; quantum chemical calculations; ThDP-dependent; Introduction Enzymes that depend on thiamin diphosphate (ThDP, Scheme 1) can be found in a wide range of metabolic pathways. Although they are known to catalyze the formation of C–N, C–O and C–S bonds, ThDP
1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation
Beilstein J. Org. Chem. 2018, 14, 2940–2948, doi:10.3762/bjoc.14.273
- ], exists exclusively as a Z-isomer (Figure 2b). Moreover, gas phase quantum chemical calculations show that the E-form is preferable for 5a (ΔE = EZ − EE = 1.66 kcal/mol), 6a (ΔE = 1.19 kcal/mol), and 7a (ΔE = 1.90 kcal/mol), while the Z-form dominates for 4a (ΔE = −2.62 kcal/mol, Figure 3). The
- of the Z-form through formation of a stronger hydrogen bond between the DMSO molecule and the NHb proton [11], which is sterically unhindered and accessible for the solvent. Indeed, X-ray data and quantum chemical calculations show that phenyl and naphthalene rings are almost perpendicular (Figure 2
Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules
Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190
- experiments and quantum chemical calculations, the wheels cannot be fully disengaged; however, the wheel–wheel interactions strongly differ for the different oxidation states. The controlled clutching and declutching of 23 by electrochemical stimuli is reminiscent of the operation of a macroscopic friction
Synthesis of new p-tert-butylcalix[4]arene-based polyammonium triazolyl amphiphiles and their binding with nucleoside phosphates
Beilstein J. Org. Chem. 2018, 14, 1980–1993, doi:10.3762/bjoc.14.173
- solution was filtered through a 1.2 µm filter and kept at 4 °C for 12 h. Polymerization was carried out by irradiating the solutions with 254 nm UV light (1 mW/cm2) for 15 min under vigorous stirring in 10 mm quartz cuvettes, placed in a thermostat holder at 25 °C. Quantum chemical calculations Quantum
- chemical calculations were done in several steps: selection of optimal conformers; organization of initial complex geometry; complex optimization procedure. The conformers search procedure has been done only for calix[4]arene’s triazolyl substituents due to complexity of the whole molecule. Conformers of
The phenyl vinyl ether–methanol complex: a model system for quantum chemistry benchmarking
Beilstein J. Org. Chem. 2018, 14, 1642–1654, doi:10.3762/bjoc.14.140
- -docking motifs via the phenyl and vinyl moieties, with an additional less populated OH∙∙∙P(phenyl)-bound isomer detected only by microwave spectroscopy. The correct prediction of the energetic order of the isomers using quantum-chemical calculations turns out to be challenging and succeeds with a
- electronically excited (S1) state is analyzed, in which a destabilization of the OH∙∙∙O structure compared to the S0 state is observed experimentally and theoretically. Keywords: dispersion interactions; IR spectroscopy; quantum-chemical calculations; rotational spectroscopy; structure determination; weak
- Fourier transform microwave (CP-FTMW) spectroscopy. Comparing spectroscopic results with quantum-chemical calculations is often mandatory for the interpretation of experiments. Furthermore, such comparison enables a critical evaluation of the approximations used, comparing the relative stability of
[3 + 2]-Cycloaddition reaction of sydnones with alkynes
Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113
- quantum chemical calculations (DFT/B3LYP-6-31G*) [81] steric effects were identified as the main factor influencing the ratio of both regioisomers. These calculations clearly proved the almost apolar character of both possible transition states giving 3- and 4-BPin substituted pyrazoles through bicyclic
Volatiles from three genome sequenced fungi from the genus Aspergillus
Beilstein J. Org. Chem. 2018, 14, 900–910, doi:10.3762/bjoc.14.77
- product 9 is observed. From A, a second cyclisation event results in D that yields 12 upon deprotonation. Alternatively, A can react by a 1,5-proton shift to E, followed by cyclisation to F and deprotonation to H. This mechanism is favoured by quantum chemical calculations [35] and provides a reasonable
An uracil-linked hydroxyflavone probe for the recognition of ATP
Beilstein J. Org. Chem. 2018, 14, 747–755, doi:10.3762/bjoc.14.63
- ratiometric fluorescent nature. First, we examined the possible structure and the supramolecular interactions by quantum chemical calculations of our target compound, UHF (uracil-hydroxyflavone) and ATP (see Figure 1 for structures). The theoretical results indicated the possibility of base-pairing
Investigations towards the stereoselective organocatalyzed Michael addition of dimethyl malonate to a racemic nitroalkene: possible route to the 4-methylpregabalin core structure
Beilstein J. Org. Chem. 2018, 14, 553–559, doi:10.3762/bjoc.14.42
- % determined by NMR). Using quantum chemical calculations, we propose approximate transition state models for the stereoselective Michael addition (Figure 2). Geometrical optimizations were performed at HF/6-31G* level and energies were further refined using M06-2X functional with 6-311+G** basis set
- purity of the major diastereomer (er 99:1). With the help of quantum-chemical calculations, we have proposed a transition state model for the Michael addition. Structures of pregabalin and methylpregabalin. Transition state models for the reaction of (R)-6 with dimethyl malonate using catalyst C7 (M06-2X
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