Fluorine effect in nucleophilic fluorination at C4 of 1,6-anhydro-2,3-dideoxy-2,3-difluoro-β-D-hexopyranose

• Danny Lainé,
• Vincent Denavit,
• Olivier Lessard,
• Laurie Carrier,
• Charles-Émile Fecteau,
• Paul A. Johnson and
• Denis Giguère

Beilstein J. Org. Chem. 2020, 16, 2880–2887, doi:10.3762/bjoc.16.237

• destabilize the adjacent carbocation center [41][42][43], avoiding 1,2-alkyl shift, and thus formation of byproduct 20. Similarly, the large dipole moment of the C–F bond at C2 influences the outcome of the deoxyfluorination at C4 [3]. For triflates 16 and 17, both dipoles (green arrows, Figure 3a) are

Conformational preferences of fluorine-containing agrochemicals and their implications for lipophilicity prediction

• Daniela Rodrigues Silva,
• Joyce K. Daré and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2020, 16, 2469–2476, doi:10.3762/bjoc.16.200

• lipophilicity with the molecular conformation. Keywords: dipole moment; fluorinated compounds; gauche effect; herbicides; log P; Introduction Whilst in the last years the agrochemical industry has encountered a period of downturn affected by new regulations, low crop prices, biochemical resistance, among

• employed to describe lipophilicity. It has been previously established that the lipophilicity of a compound depends greatly on the overall molecular polarity [15], which is often expressed as the molecular dipole moment (μ). In turn, the orientation of polar bonds also influences the overall polarity of an

• polar solvent (e.g. water), however, decreases the difference in energy among conformers and Igg becomes the most stable conformer in solution, i.e., a double gauche effect takes place (see data in parentheses in Figure 2). This is not surprising, since Igg has the highest dipole moment (data shown in

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• of ICT for electronic state modification in the excited state of the molecules [45]. In this state, all dyes have a notably higher dipole moment and a lower LUMO energy level as compared to their ground state [46][47][48][49]. Increasing the electron-donating strength of the various heterocyclic

• scalar product, μβ(2ω), of the vector component of the first hyperpolarizability tensor, β, and the dipole moment vector [58][59][60][61]. This product is derived according to Equation 1 considering γ0(−2ω,ω,ω,0), the third-order term, as negligible for the push-pull dyes under consideration. This

• exhibited a higher NLO response than their analogs 3–7. In order to obtain an insight into the NLO properties of the studied dyes, the first-order hyperpolarizability (β) and dipole moment (µ) were calculated at the B3LYP/6-31+G(d,p) level of theory in CHCl3. In general, a high NLO response for a typical

Naphthalene diimide bis-guanidinio-carbonyl-pyrrole as a pH-switchable threading DNA intercalator

• Poulami Jana,
• Filip Šupljika,
• Carsten Schmuck and
• Ivo Piantanida

Beilstein J. Org. Chem. 2020, 16, 2201–2211, doi:10.3762/bjoc.16.185

• absence of ICD bands within the naphthalene diimide absorption range (350–420 nm) suggested that the NDI transition dipole moment associated with the higher energy transition (NDI longer axis) was not well-oriented in respect to the DNA chiral axis [14]. At variance to ds-DNA, the addition of compound 4

Naphthalene diimide–amino acid conjugates as novel fluorimetric and CD probes for differentiation between ds-DNA and ds-RNA

• Annike Weißenstein,
• Myroslav O. Vysotsky,
• Ivo Piantanida and
• Frank Würthner

Beilstein J. Org. Chem. 2020, 16, 2032–2045, doi:10.3762/bjoc.16.170

• ). The transition dipole moment associated with the HOMO-to-LUMO transition in the visible range (red arrow) and with the higher energy transition (blue arrow) are respectively shown superimposed on the minimised structure. Interactions of 3a,b, and 5 with ds-DNA/RNA For a study of interactions with

• transition dipole moment with respect to the DNA chiral axis [50]. A positive sign observed for 3a suggests that the long axis of the NDI chromophore is perpendicular to the longitudinal axis of the base pairs (red arrow in Figure 8, for 3a), while a negative one observed for 3b suggests a parallel

• ). b) The molecular ground state dipole moment is indicated by the black arrow. The transition dipole moments calculated by TD-DFT (at the B3LYP/6-31+G** level of theory) for the lowest transitions in the visible range of the spectrum (indicated in the spectra by the red and blue arrows) are shown

Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines

• Vladimir Kubyshkin

Beilstein J. Org. Chem. 2020, 16, 1837–1852, doi:10.3762/bjoc.16.151

• . The existence of the minor conformations will also be relevant in the explanation of the amide-rotation barriers (vide infra). It should be noted that calculation of the net dipole is of little aid when accessing polarity of the model compounds 1–4 [77]. For example, the dipole moment calculated for

Models of necessity

• Timothy Clark and
• Martin G. Hicks

Beilstein J. Org. Chem. 2020, 16, 1649–1661, doi:10.3762/bjoc.16.137

• how well the results fit with the user’s own preferences and prejudices. Take, for instance, the concepts of polarization and charge transfer. Of these two closely related concepts, polarization is real and observable (e.g., through a change in dipole moment), whereas charge transfer is a qualitative

• net atomic charges) and of the bond. Physically, both result in the same change in dipole moment. Objectively, they are not distinguishable, as has been pointed out many times [33]. Quantum mechanics to Lewis or the reverse? The preceding section could easily be expanded into a complete book but

• . Conceptual distinction between polarization and charge transfer. The distinction depends entirely on the definition of the atoms, and even the bond. In both cases, the result is the same increase in dipole moment. The vertical dashed lines indicate notional borders between atoms. The two phenomena are

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• close dielectric constant (ε = 4.7 for CHCl3 and 8.9 for DCM) [28], the similar polarity index (P = 2.7 for CHCl3 and 3.1 for DCM) [29][30][31], and the very close dipole moment (1.15 for CHCl3, 1.14 for DCM) [32], the conformation of the compounds should be almost the same in the NMR solvent and in the

Synthesis, antiinflammatory activity, and molecular docking studies of bisphosphonic esters as potential MMP-8 and MMP-9 inhibitors

• Abimelek Cortes-Pacheco,
• María Adelina Jiménez-Arellanes,
• Francisco José Palacios-Can,
• José Antonio Valcarcel-Gamiño,
• Rodrigo Said Razo-Hernández,
• María del Carmen Juárez-Vázquez,
• Adolfo López-Torres and
• Oscar Abelardo Ramírez-Marroquín

Beilstein J. Org. Chem. 2020, 16, 1277–1287, doi:10.3762/bjoc.16.108

• small molecular volume increases the pharmacokinetic abilities of the compounds. In addition, 3 and 4 have a greater dipole moment compared to 5 and 6. The hydrogen-bond formation and the noncovalent interactions are influenced by the dipole moment. This means that an increased dipole moment can improve

• the binding properties of a molecule. Besides the dipole moment, 3 and 4 have the greatest chemical hardness of the bisphosphonates. This descriptor is related to the chemical susceptibility to an external potential. Therefore, the antiinflammatory activity of these compounds can be related to the

• size (volume), solvation (dipole moment), and chemical reactivity (hardness; probably related to a minor metabolic biotransformation). These descriptors can be associated with the better pharmacokinetic profile of the derivatives 3 and 4 by oral administration. Molecular docking As a second

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• , and its dipole moment in the benzene solution was measured (2.90 D). Besides the mentioned sterically hindered iminoxyl radicals 8 and 16, iminoxyl radicals with electron-withdrawing substituents at the C=NO• fragment also demonstrate increased stability compared to ordinary alkyl and aryl iminoxyl

Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

• Nuray Altinolcek,
• Ahmet Battal,
• Mustafa Tavasli,
• William J. Peveler,
• Holly A. Yu and
• Peter J. Skabara

Beilstein J. Org. Chem. 2020, 16, 1066–1074, doi:10.3762/bjoc.16.93

• . This indicates that the excited state dipole moment is much greater than the ground state dipole moment. Quantum yields The relative fluorescent quantum yields (ϕFL) of compounds 7a and 7b were determined in dichloromethane by using rhodamine B (ϕFL = 49% at λexc=355 nm) in ethanol as reference [45

Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes

• Zeguo Fang,
• Nawaf Al-Maharik,
• Peer Kirsch,
• Matthias Bremer,
• Alexandra M. Z. Slawin and
• David O’Hagan

Beilstein J. Org. Chem. 2020, 16, 674–680, doi:10.3762/bjoc.16.65

• the requirements for different LCD technologies. For the traditional twisted nematic (TN) LCD technology, devices require liquid crystals with display positive dielectric anisotropy by which the molecular dipole moment is oriented parallel to the long axis of the molecule, while for the current

• adopt conformations with low overall molecular polarities. A comparison of the Δε for 8 and 9 illustrates that incorporation of the third alpha-fluorine lowers the overall Δε value. This is presumably due to a resulting decrease in the overall molecular dipole moment () along the minor axis. When an

• structure to the more rigid spiro structure 11a, brought about a dramatic enhancement of the molecular dipole moment (μ||), resulting in a much more positive and increased parameter value (Δε = 4.8). This experimental value was close to the predicted calculated value (Δε = 4.3) as shown in Table 2. It is

Synthesis, liquid crystalline behaviour and structure–property relationships of 1,3-bis(5-substituted-1,3,4-oxadiazol-2-yl)benzenes

• Afef Mabrouki,
• Malek Fouzai,
• Armand Soldera,
• Abdelkader Kriaa and
• Ahmed Hedhli

Beilstein J. Org. Chem. 2020, 16, 149–158, doi:10.3762/bjoc.16.17

• moments were also investigated. Keywords: dipole moment; fluorine; liquid crystal; oxadiazole; Introduction Liquid-crystalline (LC) materials have been known for over a century [1]. It is clear that architecture and functionalization are essential aspects in molecular engineering of liquid crystals [2

• high 2θ-region of Figure 4, slightly different values of the d-spacings calculated from these peaks suggest a weakly distorted hexagonal lattice [34]. Structure–conformation relationships Molecular dipole moment Calculated electric dipole moments of compounds 2 and 4 are reported in Table 3. The

• the vectors of the dipole moments of compounds 4c, 4b and 2b are shown. In Figure 7 we plotted the calculated dipole moments. To quantify the effect of terminal chains, we calculated the dipole moment µ0 of 1,3-bis(1,3,4-oxadiazol-2-yl)benzene (RC) as it contains no terminal tails and can serve as

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• relative to the ones of the DNA base pairs [75][76]. Considering a dipole moment of the donor–acceptor systems 3a–c along the long molecular axis, a binding mode in which the ligand is accommodated in the intercalation site with its long molecular axis perpendicular to the long axis of the binding site

• reminiscent of the high stereoselectivity observed for [2 + 2] photodimerizations in organized media or in the solid state [37][38][39][40][41]. Considering the pronounced donor–acceptor interplay in 3b and 3c and the resulting strong dipole moment, it may be proposed that these compounds form dimeric

• coupling of its transition dipole moment with the ones of the DNA bases. Overall, these data revealed a loose binding of the cyclobutane derivative 4b to DNA through outside-edge binding of the ligand that enabled the association of one or two aromatic units in the DNA grooves. Photoswitching of the DNA

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• with increasing solvent polarity in a range from green fluorescence (529 nm) in toluene to red fluorescence in DMSO (638 nm) (Figure 12). The observed positive emission solvatochromism is a consequence of a significant change in the dipole moment from the electronic ground to the vibrationally relaxed

• ). The Onsager radius a, assuming a spherical dipole to approximate the molecular volume of the molecule in solution, was estimated from the optimized ground-state structure of compound 6c obtained by DFT calculations. With an a value of 5.46 Å, the change in dipole moment was calculated to 11.6 D (3.87

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

• Aydan Yadigarli,
• Qimeng Song,
• Sergey I. Druzhinin and
• Holger Schönherr

Beilstein J. Org. Chem. 2019, 15, 2552–2562, doi:10.3762/bjoc.15.248

• optical transition. New types of solvatochromic plots of emission frequency against absorption frequency and vice versa afforded the Onsager radius-free estimation of the ground and excited states dipole moment ratio. With this approach the values of these dipole moments of 11.97 D and 18.30–19.16 D

• NR molecules in the ground state and slow sub-glass transition (Tg) relaxations in PMMA. Keywords: charge transfer; dipole moment; fluorescence; inhomogeneous broadening; oxazine dye; polarity probe; polymer permittivity; Introduction The chain and segment mobility as well as the permittivity of

• fluorescence (Figure 2a). This behavior for NR [35] is similar to donor–acceptor-substituted stilbenes [36][37], benzenes [38][39] and aminocoumarins [35][40][41]. This effect is caused by solvent relaxation around dipolar solutes that possess in the lowest excited state a substantially higher dipole moment

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• similar to that of hydrogen atoms. Due to these unique properties, the introduction of fluorine into a molecule can cause dramatic changes, such as the acidity or basicity of neighboring groups, dipole moment, and properties such as lipophilicity, metabolic stability, and bioavailability [1]. Consequently

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• MeCN at elevated temperature (60 °C), following the works of Hecht and co-workers [45][46]. The data is presented in Table 2. Additionally, we studied A3 in a wide range of temperatures in MeCN. The half-lives decrease from A1 to A3, an effect that correlates with the increase in dipole moment of the

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)₂A fluorescent dyes

• Keiichi Imato,
• Toshiaki Enoki,
• Koji Uenaka and
• Yousuke Ooyama

Beilstein J. Org. Chem. 2019, 15, 1712–1721, doi:10.3762/bjoc.15.167

• polarity (i.e., positive fluorescence solvatochromism). The Lippert–Mataga plots for OUY-2, OUK-2 and OUJ-2 indicate that the Δμ (= μe − μg) value, which is the difference in the dipole moment of the dye between the excited (μe) and the ground (μg) states, increases in the order of OUY-2 < OUK-2 < OUJ-2

• the fluorescence maximum and the dipole moment of dye molecule on the basis of the Lippert–Mataga equation (Equation 1) [44][45][46]: where Consequently, on the basis of Equation (1) and Equation (2), the change in the dipole moment, Δμ = μe − μg, between the ground (μg) and the excited (μe) states

• with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert–Mataga plots revealed that the difference in the dipole moment of the dye between the excited state and the ground state increases in the order of OUY-2 < OUK-2 < OUJ-2. Thus, the fact explains our findings that

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• -accepting structures. An increase in charge separation within ICT probes would occur upon excitation which results in a larger dipole moment in the excited state. The energy of the excited state with a larger dipole moment could be reduced by interaction with a high polarity environment and could be

Synthesis of dipolar molecular rotors as linkers for metal-organic frameworks

• Sebastian Hamer,
• Fynn Röhricht,
• Marius Jakoby,
• Ian A. Howard,
• Xianghui Zhang,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1331–1338, doi:10.3762/bjoc.15.132

• the central phenylene core. A combination of 1,4-dioxane annelation and dicyano substitution generates a theoretically predicted, very high dipole moment of 10.1 Debye. Moreover, the molecules are sufficiently small to fit into cavities of 10 Å3. Hence, the dipolar rotors should be ideally suited as

• linkers in MOFs with potential applications as ferroelectric materials and for optical signal processing. Keywords: benzothiadiazole; dipolar rotor; fluorescence; large dipole moment; metal organic framework linker; Introduction Rotors are among the fundamental functional units in engineering in our

• of the dipolar rotors must be compatible with MOF growth. Preconditions 1. and 2. are somewhat contradicting each other. In the most simple treatment, the dipole moment is proportional to the point charges times their distance. However, in a real chemical situation the distance between the charges

Efficient synthesis of pyrazolopyridines containing a chromane backbone through domino reaction

• Razieh Navari,
• Saeed Balalaie,
• Saber Mehrparvar,
• Fatemeh Darvish,
• Frank Rominger,
• Fatima Hamdan and
• Sattar Mirzaie

Beilstein J. Org. Chem. 2019, 15, 874–880, doi:10.3762/bjoc.15.85

• . The use of a protic solvent seems to be essential for the progress of the reaction and may related to the dipole moment and also the hydrogen-bonding ability of protic solvents. The spectroscopic data confirmed the formation of 4a. The X-ray crystallographic data of compound 4a confirmed the structure

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

• Andrejs Šišuļins,
• Jonas Bucevičius,
• Yu-Ting Tseng,
• Irina Novosjolova,
• Kaspars Traskovskis,
• Ērika Bizdēna,
• Huan-Tsung Chang,
• Sigitas Tumkevičius and
• Māris Turks

Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41

• showed pronounced changes with solvent polarity in terms of emission maxima and quantum yields, though the absorption spectra showed minor or no changes with increasing solvent polarity indicating small dipole moment in the ground state. A good linear correlation between the fluorescence QY and the

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

• ., polyaromatic hydrocarbons) induces a dipole moment; likewise, when a spherical charge distribution is deformed to an ellipsoid, a quadrupole is induced. Discussion of WMI, as found in the chemical literature, often suffers from a profound confusion of tongues due to the preference of a folkloristic [12

The phenyl vinyl ether–methanol complex: a model system for quantum chemistry benchmarking

• Dominic Bernhard,
• Fabian Dietrich,
• Mariyam Fatima,
• Cristóbal Pérez,
• Hannes C. Gottschalk,
• Axel Wuttke,
• Ricardo A. Mata,
• Martin A. Suhm,
• Melanie Schnell and
• Markus Gerhards

Beilstein J. Org. Chem. 2018, 14, 1642–1654, doi:10.3762/bjoc.14.140

• complex, however, we find that the B3LYP-D3(BJ)/def2-TZVP level of theory provides a better prediction of the magnitudes of the dipole-moment components. Experimentally, we only observe a-type transitions for this complex, which points to rather low values for μb and μc. SCS-CC2 calculations predict all

• three dipole-moment components to be of comparable magnitude. At the B3LYP-D3(BJ) level, μa is predicted to be significantly stronger than μb and μc. This change in magnitude for the dipole-moment components for different levels of calculation is more often observed for weakly bound complexes because

• the exact arrangement of the two monomers with respect to each other can have a major influence on the dipole-moment components. Also note that in none of the spectroscopic experiments, we observe the OH–E isomer that is also predicted to be of relatively low energy (cf. Table 1). The rotational