Conformational study of L-methionine and L-cysteine derivatives through quantum chemical calculations and ³J_HH 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

• introduced. Using the IEF−PCM implicit solvent model, small changes in the populations of conformers of 1 are observed when the solvent dielectric constant (ε) is increased. However, these slight variations do not affect the total populations of conformers a, b and c, and thus, it is an indicative that the

• studied media. In isolated phase, the conformer 3-trans-Ia represents 45.6% of the conformational equilibrium of 3, but when the dielectric constant of the medium is increased, this geometry is destabilized and has its population decreased to 34.8%. The same tendency is observed for 4-trans-Ia, which has

• investigated through experimental 3JHH coupling constant obtained from 1H NMR spectroscopy and the corresponding calculated ones (Table 6). For the compound 3, the experimental data show that the 3JHaHb1,obs and 3JHaHb2,obs coupling constants vary when the dielectric constant of the solvent (ε) is increased

The synthesis of α-aryl-α-aminophosphonates and α-aryl-α-aminophosphine oxides by the microwave-assisted Pudovik reaction

• Erika Bálint,
• Ádám Tajti,
• Anna Ádám,
• István Csontos,
• Konstantin Karaghiosoff,
• Mátyás Czugler,
• Péter Ábrányi-Balogh and
• György Keglevich

Beilstein J. Org. Chem. 2017, 13, 76–86, doi:10.3762/bjoc.13.10

• B3LYP/6-31G (d,p) method. In the solvent-free reaction, the dielectric constant of the P reagent was estimated as 78.3553. This value was taken into account as an implicit solvent effect. First, the tautomeric equilibria of dialkyl phosphites and diphenylphosphine oxide were studied (Table 8). It was

Synthesis, structure, and mechanical properties of silica nanocomposite polyrotaxane gels

• Kazuaki Kato,
• Daisuke Matsui,
• Koichi Mayumi and
• Kohzo Ito

Beilstein J. Org. Chem. 2015, 11, 2194–2201, doi:10.3762/bjoc.11.238

• generating systems, nanocomposites should satisfy both a high dielectric constant that is assured by the nanoparticles and a low elastic modulus [7]. Mechanically interlocked supramolecular polymers, such as polyrotaxane [8][9], can control the interface between the matrix polymer and the nanoparticles

Mechanism, kinetics and selectivity of selenocyclization of 5-alkenylhydantoins: an experimental and computational study

• Biljana M. Šmit,
• Radoslav Z. Pavlović,
• Dejan A. Milenković and
• Zoran S. Marković

Beilstein J. Org. Chem. 2015, 11, 1865–1875, doi:10.3762/bjoc.11.200

• used. Full geometry optimizations, without any symmetry constraints, and frequency calculations were performed for all species in acetonitrile as solvent (dielectric constant = 35.688) using the SMD solvation model [44]. SMD is a continuum solvation model based on the quantum mechanical charge density

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity

• Karolina Żukowska,
• Eva Pump,
• Aleksandra E. Pazio,
• Krzysztof Woźniak,
• Luigi Cavallo and
• Christian Slugovc

Beilstein J. Org. Chem. 2015, 11, 1458–1468, doi:10.3762/bjoc.11.158

• stabilized in solvents with high dielectric constants (such as CH2Cl2) than in solvents with low dielectric constants [27], the trans–cis energies were calculated in toluene (as an example for a solvent with low dielectric constant). In this case, 5a is still preferably in the cis configuration (cis-5a is

Formation of nanoparticles by cooperative inclusion between (S)-camptothecin-modified dextrans and β-cyclodextrin polymers

• Thorbjørn Terndrup Nielsen,
• Catherine Amiel,
• Laurent Duroux,
• Kim Lambertsen Larsen,
• Lars Wagner Städe,
• Reinhard Wimmer and
• Véronique Wintgens

Beilstein J. Org. Chem. 2015, 11, 147–154, doi:10.3762/bjoc.11.14

• increased D70HPβ-CD concentration (0–2 mM) is observed. This is typical for a decrease in local dielectric constant (i.e., shielding from water solvent) and thereby an indicator of inclusion of the pendant CPT in the apolar β-CD cavities. Ka values were determined by plotting the variation in FI at 430 nm

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

• Paweł Borowiecki,
• Daniel Paprocki and
• Maciej Dranka

Beilstein J. Org. Chem. 2014, 10, 3038–3055, doi:10.3762/bjoc.10.322

• (±)-3 as well as a good enzymatic activity and selectivity are retained, is being of particular significance for the overall success of the process. Five different apolar organic solvents (varying in log P, dielectric constant ε, dipolar moment μ) including: n-hexane, pentane, toluene, MTBE, and diethyl

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

• Roman Matthessen,
• Jan Fransaer,
• Koen Binnemans and
• Dirk E. De Vos

Beilstein J. Org. Chem. 2014, 10, 2484–2500, doi:10.3762/bjoc.10.260

• and C10 [44]. The use of acetonitrile as solvent is ideal when working in an undivided cell, thanks to its adequate oxidation stability and high dielectric constant. Anhydrous conditions and the easier oxidation of oxalate and formate, at a Pt anode, compared to butadiene and the cathodically

Photo, thermal and chemical degradation of riboflavin

• Muhammad Ali Sheraz,
• Sadia Hafeez Kazi,
• Sofia Ahmed,
• Zubair Anwar and
• Iqbal Ahmad

Beilstein J. Org. Chem. 2014, 10, 1999–2012, doi:10.3762/bjoc.10.208

• , dioxane and its mixtures with water, ethanol and pyridine [96][97][98]. The photodegradation of RF has been found to be more rapid in organic solvents as compared to aqueous solutions [97][99]. This could be linked to the physical properties of the solvents such as polarity, dielectric constant, viscosity

• , etc. [27][32][83][100][101]. The dielectric constant of the medium has been shown to affect complexation between RF and cloxacillin sodium in aqueous–ethanol media and found to decrease with an increase in temperature [102]. A 7–10% increase in the solubility of RF was observed when dissolved in

• photolysis of FMF was found to be affected by the dielectric constants of the solvents, i.e., greater the dielectric constant higher the rate of photolysis. This indicated the involvement of a polar intermediate along the reaction pathway [50]. The values of the second-order rate constants for the aerobic

Supercritical carbon dioxide: a solvent like no other

• Jocelyn Peach and
• Julian Eastoe

Beilstein J. Org. Chem. 2014, 10, 1878–1895, doi:10.3762/bjoc.10.196

• properties ordinarily required for an effective solvent, with a lower viscosity, dielectric constant [26][27] and surface tension in comparison to other common reference solvents. Also, as CO2 is a linear molecule with no net dipole moment there is significant difficulty dissolving polar and ionic species

• constant R and temperature T divided by molar volume (Vm). As CO2 also has a low dielectric constant, α/υ and δ, it is expected that fluorocarbons and CO2 will be more compatible than HCs and CO2. It can therefore be said that fluorocarbons are more CO2-philic than the corresponding hydrocarbons. A range

• dielectric constant) than the respective hydrocarbon counterparts. There has been success in the design and synthesis of non-fluorinated polymers and surfactants, with hydrocarbon based, siloxane based and carbonyl and oxygenated hydrocarbon surfactants and polymers successfully solubilised [11][12][13][26

Why a diaminopyrrolic tripodal receptor binds mannosides in acetonitrile but not in water?

• Diogo Vila-Viçosa,
• Oscar Francesconi and
• Miguel Machuqueiro

Beilstein J. Org. Chem. 2014, 10, 1513–1523, doi:10.3762/bjoc.10.156

• lists were updated every 5 steps (10 fs). Electrostatic long range interactions were treated with a generalized reaction field [47] with an ionic strength of 0.1 M and a relative dielectric constant of 54 for systems with water [48] and 35.84 for systems solvated with acetonitrile [49]. The v-rescale

• force field. The model compound pKa value used (10.64 for all equivalent amino groups) is the pKa of the dimethylamine [54]. It was used a dielectric constant of 2 for the solute and 80 for the solvent. Grid spacing of 0.1 nm, in the coarser calculation, and 0.025 nm, in the focusing procedure, were

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• (polarizable continuum model) method; the IEFPCM (integral equation formalism PCM) method coupled to UA0 radii was used. The mechanisms were studied with both EtOAc and DMF solvents with a dielectric constant ε of 5.99 and 37.21, respectively. The hardness η is related to the hard–soft-acid-basis (HSAB

Temperature measurements with two different IR sensors in a continuous-flow microwave heated system

• Jonas Rydfjord,
• Fredrik Svensson,
• Magnus Fagrell,
• Jonas Sävmarker,
• Måns Thulin and
• Mats Larhed

Beilstein J. Org. Chem. 2013, 9, 2079–2087, doi:10.3762/bjoc.9.244

• (specific heat capacity, dipolar moment, dielectric constant and tan δ) as explanatory variables (Table 2, model 1). This full model provided an adjusted R2 value of 0.985 (Table 2, model 1). Removing non-significant variables (99.9% level) from this model gave a new model (Table 2, model 2) with an

• sensor 2 In accordance with the results for IR sensor 1, a linear multiple regression model was constructed with the set temperature, flow rate and solvent properties (specific heat capacity, dipolar moment, dielectric constant and tan δ) as explanatory variables (Table 3, model 1). This comprehensive

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

• carbon dioxide to deliver product 8 without undergoing further cyclization to yield either 6 or 7, possibly due to the lower dielectric constant of THF (7.42) compared to methanol (32.7) (Scheme 3). As is evident from Scheme 3, there are three possible tautomeric forms for 8, viz. 8x, 8y, 8z for the

Microwave-assisted three-component domino reaction: Synthesis of indolodiazepinotriazoles

• Rajesh K. Arigela,
• Sudhir K. Sharma,
• Brijesh Kumar and
• Bijoy Kundu

Beilstein J. Org. Chem. 2013, 9, 401–405, doi:10.3762/bjoc.9.41

• % isolated yield, which was characterized as 2-[2-(4-methylphenyl)ethynyl]-1-(oxiran-2-ylmethyl)-1H-indole (4a, Table 1, entry 4). In contrast, use of the polar aprotic solvent DMF with high dielectric constant produced both intermediates 4a/5a as well as the annulated product 6a. Interestingly, a

The β-cyclodextrin/benzene complex and its hydrogen bonds – a theoretical study using molecular dynamics, quantum mechanics and COSMO-RS

• Jutta Erika Helga Köhler and
• Nicole Grczelschak-Mick

Beilstein J. Org. Chem. 2013, 9, 118–134, doi:10.3762/bjoc.9.15

• vacuo (.energy files) and the COSMO-RS structure (.cosmo files), the latter being optimised in a dielectric field with the dielectric constant of water (the value of the dielectric constant is a variable in the COSMO-RS program and can be chosen by the user). Up to now it was possible to calculate

A bisazobenzene crosslinker that isomerizes with visible light

• Subhas Samanta,
• Harris I. Qureshi and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2012, 8, 2184–2190, doi:10.3762/bjoc.8.246

• -isomers (force constant 16). Molecular dynamics runs were performed in vacuo, essentially as described previously [36], with a distance-dependent dielectric constant, and 1–4 scale factors of 0.833 for electrostatic and 0.5 for van der Waals interactions, a step size of 1 fs and 300 K as the simulation

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• reversibly interconverted, with at least one of the reactions being induced by light excitation, between two forms with different absorption spectra [15]. These two forms differ also in many other physical properties, such as their redox potential, fluorescent intensity, acid/base strength, dielectric

• constant, dipolar moment, molecular shape, and so on. Traditionally, this type of organic system has been widely used for analytical purposes, but at the present moment, they are widely required for many technical uses, for instance, binary systems for logic gates in computing or signal transmission

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system

• Caterina Fraschetti,
• Matthias C. Letzel,
• Antonello Filippi,
• Maurizio Speranza and
• Jochen Mattay

Beilstein J. Org. Chem. 2012, 8, 539–550, doi:10.3762/bjoc.8.62

• energy terms, such that the T molecule, and the TH+ ion even more, are locked in the skew-boat. When the dielectric constant becomes high (water), torsional and solvation factors may become comparable to intramolecular electrostatic factors, with the consequence that conformational flexibility of the

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations

• Elisa Frezza,
• Silvia Pieraccini,
• Stefania Mazzini,
• Alberta Ferrarini and
• Gian Piero Spada

Beilstein J. Org. Chem. 2012, 8, 155–163, doi:10.3762/bjoc.8.16

• moment than those of cercosporin (1), therefore 2 should be more sensitive to solvent polarity (acetone has a dielectric constant of about 20 at room temperature). HTP predictions by the SC method Within the SC approach, the HTP of a chiral dopant in a nematic solvent is proportional to the so-called

On the control of secondary carbanion structure utilising ligand effects during directed metallation

• Andrew E. H. Wheatley,
• Jonathan Clayden,
• Ian H. Hillier,
• Alison Campbell Smith,
• Mark A. Vincent,
• Laurence J. Taylor and
• Joanna Haywood

Beilstein J. Org. Chem. 2012, 8, 50–60, doi:10.3762/bjoc.8.5

• condensed phase effects, using the CPCM model (at the B3LYP/6-311++G(2df,2dp) level) with a dielectric constant of 2.37, were included. Molecular structure of 6-Lil·PMDTA; H-atoms (excl. H8) omitted for clarity. Selected bond lengths (Å) and angles (°): O1–Li1 1.845(3), N2–Li1 2.116(4), N3–Li1 2.097(3), N4

NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas

• Damjan Makuc,
• Jennifer R. Hiscock,
• Mark E. Light,
• Philip A. Gale and
• Janez Plavec

Beilstein J. Org. Chem. 2011, 7, 1205–1214, doi:10.3762/bjoc.7.140

• surface. Relative energies in solution were calculated by means of Tomasi's polarized continuum model, where the dielectric constant of DMSO was used (ε = 46.7). Anion receptors 1–4 together with their atomic numbering scheme. 1H NMR spectra of 1 in the absence of anions (a) and upon addition of one

Anion–π interactions influence pK_a values

• Christopher J. Cadman and
• Anna K. Croft

Beilstein J. Org. Chem. 2011, 7, 320–328, doi:10.3762/bjoc.7.42

• hydrogen bonds to the parent acid. This does not occur to a significant extent in water, as the water forms strong hydrogen bonds with itself. The extent of homoconjugation that may occur can be gauged by the dielectric constant (ε) of the solvent, where a lower dielectric constant corresponds to a higher

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• solvents favouring the formation of the monometallic species [15]. Propylene carbonate is a polar aprotic solvent with a dielectric constant of 65 [81], and therefore the concentration of catalytically active bimetallic complex 1 will be reduced in this solvent resulting in less effective catalysis

• carbonate. The reason for the lack of formation of bimetallic complexes in propylene carbonate is probably due to the polarity of the solvent (dielectric constant 65 [81]), which will stabilise the highly polar V=O bonds present in the mononuclear species. Having determined the order with respect to

Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

• Ritesh Nandy and
• Sethuraman Sankararaman

Beilstein J. Org. Chem. 2010, 6, 992–1001, doi:10.3762/bjoc.6.112

• of the energy of the dipole on the dielectric constant and refractive index of the solvent. The Lippert–Mataga equation accounts for the general solvent effect and does not account for specific solvent–fluorophore interactions, for example, through hydrogen bonding etc. The Lippert–Mataga plot for 1c