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

• moments within a molecule cancel each other out, the molecule will not be polar. Any molecule with an inversion centre, a horizontal mirror plane (σh), or multiple Cn axes will not have dipole moments and therefore will not be polar, (C1, Cs, C∞h, D∞h Cn and Cnv do not have a dipole moment). CO2 has a

• di-CF1 having the minimum level of fluorination, Table 1, compounds 2–5), and a HC control analogue (di-C5SS, Table 1, compound 6) containing no fluorine. The study also looked at the effects of replacing a terminal fluorine atom with hydrogen (n-CF3 to n-CF2H), hereby introducing a dipole moment at

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

• evolved [71]. In 1992, Yu and coworkers reported for the first time that microwave irradiation in combination with SPPS leads to enhanced reaction rates and hence, to a higher quality of the crude peptides [72]. Microwave energy is capable of activating any molecule containing a dipole moment, which is

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• [80][81][82]. The relative planarity of 1,2,3-triazoles, the strong dipole moment (~5 D) and the ability to both donate and accept hydrogen bonds indicate the physicochemical similarities with amide bonds (Scheme 25), however, they are inert towards oxidation, hydrolysis and enzymatic degradation [88

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

• Alexander Penger,
• Cortney N. von Hahmann,
• Alexander S. Filatov and
• John T. Welch

Beilstein J. Org. Chem. 2013, 9, 2675–2680, doi:10.3762/bjoc.9.303

• number of different ylides [16]. The reactions of α-pentafluorosulfanyl carbonyl compounds are governed by a combination of the substantial dipole moment and unique steric effects of the octahedral SF5 group. Aliphatic SF5-containing derivatives of biologically active compounds are not well-known. One

Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

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

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

• ), which lie in the range of 0.002 atomic units (au) to 0.04 au, and 0.024 au to 0.139 au to electrostatic hydrogen bonds, respectively. Moreover, the H atom associated with the hydrogen bond should have a loss of atomic charge [q(H)], an increased atomic energy [E(H)], a decreased atomic first dipole

• moment [M1(H)] and a decreased atomic volume [V(H)] in comparison to those of a H atom not involved in hydrogen bonding [23]. Spectroscopic (Raman, infrared and NMR) and theoretical studies on 2-fluorophenylboronic acid have already been performed previously for assignment purposes, because of the lack

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

• , 290, 280, and 273 K for 500 ps each, and their release of the guest was analysed from these trajectories. Results and Discussion AM1 Calculations The four conformers of empty β-CD The BCDO23rO6l structure turned out to be the lowest energy conformer, also having the lowest dipole moment of only 0.5618

• Debye (dipole-moment components x = 0.0; y = 0.0; −z = 0.5618) pointing from the O6 rim towards the O23 rim of the cone. This structure is so symmetric that all its Mulliken partial atomic charges on all types of oxygen atoms were identical, e.g., equal to each average number (Table 1). Second, with

• about 6 kcal mol−1 above, was conformer BCDO23rO6r. This oval structure has the highest dipole moment of 2.5639 D (x = +0.0268; y = +0.0236; z = −2.5637) and its O6 atomic charges display a range from −0.340 to −0.349 (average −0.344), but all O2 atoms still have the same charge of 0.325, and O3 and O4

A new family of four-ring bent-core nematic liquid crystals with highly polar transverse and end groups

• Kalpana Upadhyaya,
• Venkatesh Gude,
• Golam Mohiuddin and
• Rao V. S. Nandiraju

Beilstein J. Org. Chem. 2013, 9, 26–35, doi:10.3762/bjoc.9.4

• -core mesogens; cyanobiphenyl; dipole moment; liquid crystals; nematic phase; polarity; Introduction Following the discovery of chiral and polar properties of mesomorphic bent-core compounds [1][2][3][4][5][6] the area of design, synthesis and properties of banana or bent-shaped liquid crystals (LC

• azobenzene or salicylideneimine or phenylbenzoate unit in one of the arms of the bent molecule by a polar cyanobiphenyl moiety lends stiffness to the molecule with a strong dipole moment in the lateral direction. The realization of such a molecular architecture leads to a reduction in rotational disorder as

• arm ends with a highly polar cyano group. The end cyano group in one of the arms of 1a–1c contributes to the large dipole moment. In highly polar calamitic cyanobiphenyl compounds [42][43] as well as in bent-core compounds possessing an end cyano moiety [44][45][46][47][48] the antiparallel short

Theoretical study on β-cyclodextrin inclusion complexes with propiconazole and protonated propiconazole

• Adrian Fifere,
• Narcisa Marangoci,
• Stelian Maier,
• Adina Coroaba,
• Dan Maftei and
• Mariana Pinteala

Beilstein J. Org. Chem. 2012, 8, 2191–2201, doi:10.3762/bjoc.8.247

• bonds were evidenced and, since there are no steric constraints to explain the difference between the A and B orientations in terms of stability, other forces must be considered. It is already known that cyclodextrin molecules have a rather high electric dipole moment; the correlation between this

• parameter and the complex stability by means of quantum-mechanical calculations has been previously reported [19][20]. The PP molecule has a permanent electric dipole, and the dipole–dipole interaction can make the difference between the A and B configurations. The decrease of the global dipole moment

• important to note that both in vacuo and in aqua, the guest molecules are deeply inserted in the β-CD cavity, according to the B configurations (Figure 10), and no hydrogen bonds can be evidenced. The decrease of the global dipole moment by the increase of binding energy, suggests again that dipole–dipole

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

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

• remarkable change in their physical properties, such as molecular geometry, dipole moment or absorption spectrum [12][13][14][15][16]. The isomerization process involves a decrease in the distance between the two carbon atoms in position 4 of the aromatic rings of azobenzene, from 9.0 Å in the trans form to

• 5.5 Å in the cis form (Figure 1) [17]. The trans-azobenzene is almost flat and has no dipole moment, whereas the cis isomer presents an angular geometry and a dipole moment of 3.0 D. One of the rings rotates to avoid steric repulsions due to facing of one of the π clouds of one aromatic ring to the

Liquid-crystalline heterodimesogens and ABA-heterotrimesogens comprising a bent 3,5-diphenyl-1,2,4-oxadiazole central unit

• Govindaswamy Shanker,
• Marko Prehm and
• Carsten Tschierske

Beilstein J. Org. Chem. 2012, 8, 472–485, doi:10.3762/bjoc.8.54

• distinct from that of compounds CB-Ox/n. Firstly, they have alkyl tails at both ends, and secondly, they incorporate a 1,3,4-thiadiazole unit, which is not strictly linear (bending angle 162°) [80] and within which the direction of the major dipole moment is perpendicular to the molecular long axis [80][81

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

• with the transition dipole moment directed along the long molecular axis. The electron density difference between HOMO and LUMO is shown in Figure 2; this reflects the balanced electron redistribution between the pyrimidine and phenyl moieties. Solid-state fluorescence Tris(8-hydroxyquinolinato

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

• of gauche− states was found. A possible reason for the lack of agreement between theory and experiment is the fact that calculations were performed in vacuum, whereas experiments were carried out in acetone. According to our calculations, the conformers of phleichrome (2) would have higher dipole

• 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

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

• −30 esu) showed a substantially higher dipole moment and first-order hyperpolarizability than chromophore 27a (Figure 9; μ = 10.9 D; β = 50.91 × 10−30 esu) due to a higher efficiency of D-A conjugation. Benzimidazole-derived chromophores In contrast to imidazoles, benzimidazoles possess fused benzene

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• equilibrium shifts further toward benzene oxide (more positive ΔG), suggesting that benzene oxide has the larger dipole moment. Methyl substitution at the 2- and 7-positions reverses the stability order, rendering the oxepine as the energetically favoured isomer due to the destabilizing eclipsing of the two

One-pot four-component synthesis of pyrimidyl and pyrazolyl substituted azulenes by glyoxylation–decarbonylative alkynylation–cyclocondensation sequences

• Charlotte F. Gers,
• Julia Rosellen,
• Eugen Merkul and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2011, 7, 1173–1181, doi:10.3762/bjoc.7.136

• planar, cyclic conjugation of 10 π-electrons. The dipole moment of 1a at μ = 1.08 D [20] is astoundingly large in comparison to that of naphthalene at μ = 0 D and can be rationalized by a significant contribution of cyclopentadienyl anion/tropylium cation resonance structures (Scheme 1) [19]. Since the

Predicting the UV–vis spectra of oxazine dyes

• Scott Fleming,
• Andrew Mills and
• Tell Tuttle

Beilstein J. Org. Chem. 2011, 7, 432–441, doi:10.3762/bjoc.7.56

• present. For instance, Oxazine 1 (10), Oxazine 4 (5), Resazurin (4), and Resorufin (2) have symmetry in the yz plane, and thus have vectors based almost exclusively on the y-axis. In more complex examples, the direction of dipole moment vector is predominately dictated by the positions of the amines

Anthracene appended pyridinium amide–urea conjugate in selective fluorometric sensing of L-N-acetylvaline salt

• Kumaresh Ghosh,
• Tanmay Sarkar and
• Asoke P. Chattopadhyay

Beilstein J. Org. Chem. 2010, 6, 1211–1218, doi:10.3762/bjoc.6.139

• ] and the popular b3LYP functional [38][39]. Similar calculations were also carried out on all the guests given in Table 2. For all the compounds, parameters such as global electrophilicity (ω), global electronegativity (χ), global hardness (η), dipole moment (µ) and the energies of HOMO and LUMO are

• with valine and alanine salts, DFT optimized geometry of 1 and MO energies, global hardness, global electronegativity, global electropositivity, dipole moment etc. are available. Supporting Information File 186: Detailed experimental data for 1 and 2. Acknowledgements We thank CSIR, Government of

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

• importance. In this class of molecule, the excited state is generally highly polar compared to the ground state due to intramolecular charge transfer from the donor to the acceptor group. The intramolecular charge transfer results in a large dipole moment in the excited state compared to that of the ground

• transfer quenching of fluorescence. Correlation of Stokes shifts with solvent polarity Solvent induced spectral shifts are often interpreted in terms of the Lippert–Mataga [43][44][45] equation, which describes Stokes shifts in terms of the change in the dipole moment of the fluorophore and the dependence

• and 1g are shown in Figure 5 as representative examples. From the slope of these plots the change in the dipole moment (Δμ) of the fluorophore upon electronic excitation (μES − μGS) was estimated assuming the molecular radius as the cavity radius [11]. The molecules under consideration are non

Chromo- and fluorophoric water-soluble polymers and silica particles by nucleophilic substitution reaction of poly(vinyl amine)

• Katja Hofmann,
• Ingolf Kahle,
• Frank Simon and
• Stefan Spange

Beilstein J. Org. Chem. 2010, 6, No. 79, doi:10.3762/bjoc.6.79

• dipolarity/polarizability. This correlates with a higher dipole moment of the electronically excited state. In contrast to 1-M, 1-P shows no significant influence of the π* term of the solvent on , whereas the influence of the β term is greater compared to that of 1-M. This effect reflects the impact of the

Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles

• Marjan Krasna,
• Matej Cvetko and
• Milan Ambrožič

Beilstein J. Org. Chem. 2010, 6, No. 74, doi:10.3762/bjoc.6.74

• magnetic field towards the perpendicular direction. Here we assume that originates from magnetic NPs, where μ0 is the magnetic permittivity constant and represents the magnetization of NPs due to the magnetic dipole moment . The resulting quadrupolar magnetic field free energy density change ΔfB is

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• -fluorocarbonyl compounds, but the effect decreases with the decreasing dipole moment of the carbonyl group (4–6, Figure 1a) [2]. As well as stabilising certain conformations, dipole–dipole interactions can also be responsible for destabilising other conformations. For example, in 1,3-difluoroalkanes (e.g. 7

• liquid crystals. A liquid crystal is a fluid phase in which there is some orientational ordering of the molecules. Liquid crystal display (LCD) technology requires rod-shaped molecules that have a dipole moment perpendicular to the long axis of the molecule, and this is often achieved by incorporating

• molecular conformation as well as the molecular dipole moment. The difluoro compound 60 (Figure 15) can be viewed as a conceptual progression from the axially fluorinated liquid crystal 58. NMR and modelling data show that the fluoroalkyl chain of 60 adopts a zigzag conformation in which the two C–F bonds

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Ring-alkyl connecting group effect on mesogenic properties of p-carborane derivatives and their hydrocarbon analogues

• Aleksandra Jankowiak,
• Piotr Kaszynski,
• William R. Tilford,
• Kiminori Ohta,
• Adam Januszko,
• Takashi Nagamine and
• Yasuyuki Endo

Beilstein J. Org. Chem. 2009, 5, No. 83, doi:10.3762/bjoc.5.83

• angle θ between the ring and substituent increases in the series 25, 28 < 27 < 26 or –OR, –C(O)OR < –OOCR < –CH2R. Further analysis of the computational results demonstrates that molecular dipole moment μ increases in the following order: 26 < 25 < 27 < 28. The quadrupole moment tensor Qxx perpendicular

• molecular dipole moment in phase stabilization. Since p-carboranes are moderately electron withdrawing substituents, the alkoxy derivatives have a larger dipole moment than the alkyl derivatives [16]. Alternatively, the effect can be due to higher rigidity of 1-4, which attenuates the effect as compared to

• : ethoxybenzene (25), propylbenzene (26), phenyl acetate (27), and methyl benzoate (28) and pertinent molecular parameters: dihedral angle θ, dipole moment μ, and quadrupole moment tensor QXX perpendicular to the ring plane. Preparation of diesters 16[n]. Preparation of esters 18–20. Preparation of phenol 24

Influence of spacer chain lengths and polar terminal groups on the mesomorphic properties of tethered 5-phenylpyrimidines

• Gundula F. Starkulla,
• Elisabeth Kapatsina,
• Angelika Baro,
• Frank Giesselmann,
• Stefan Tussetschläger,
• Martin Kaller and
• Sabine Laschat

Beilstein J. Org. Chem. 2009, 5, No. 63, doi:10.3762/bjoc.5.63

• twisted conformation with a dihedral angle of 43.1° [3]. The different conformations together with differences of the polarisation and dipole moment between 2- and 5-phenylpyrimidines also lead to different mesomorphic properties as was shown by Lemieux for phenylpyrimidines tethered to terminal

• nucleophilic substitution. Depending on the terminal group and the tether lengths the formation of smectic A mesophases was observed for the chloro-, bromo- and azido derivatives. Surprisingly, the strong latent dipole moment of hydroxy and cyano derivatives and the ability of hydroxy derivatives to form

Functional properties of metallomesogens modulated by molecular and supramolecular exotic arrangements

• Alessandra Crispini,
• Mauro Ghedini and
• Daniela Pucci

Beilstein J. Org. Chem. 2009, 5, No. 54, doi:10.3762/bjoc.5.54

• -mesogenic 4,4′-disubstituted 2,2′-bipyridine ligands with Pt(II) salts confirmed the role of coordination chemistry in the metal-mediated formation of liquid crystals. Indeed the induction of a dipole moment upon coordination with an MX2 moiety, allowed most of the half-disc shaped complexes [LnPtX2

• depend on the size of the X group and on the dipole moment associated with the Pt-X bond, with the sequence, for the clearing points Cl