Effect Of Fluorine Substituents Research Articles

Theoretical anharmonic Raman and infrared spectra with vibrational assignments for monofluoroaniline isomers

The ortho- meta-, and para-fluoro substituted anilines are prototype molecules for investigation of the interactions of both the amino group and the fluorine atom with the aromatic ring. The molecular structures, natural atomic charges and theoretical anharmonic Raman and infrared spectra of the three fluoroaniline isomers have been calculated by using the density functional B3LYP method with the extended 6-311++G(df,pd) basis set. The Raman and infrared spectra of 2FA, 3FA, and 4FA have been recorded. The detailed vibrational assignments of the experimental spectra have been made on the basis of the calculated potential energy distributions, PEDs. The effect of fluorine substituent on the aniline ring geometry and charge distribution, the nature of the characteristic “marker bands” and a quenching of intensities of some bands are discussed. It is shown that the frequencies of the NH 2 stretching vibrations depend on the degree of pyramidalization of the C–NH 2 group, in the isomers. In 2FA and 3FA, the NH 2 stretching frequencies are higher than those in 4FA. This corresponds to a more flattened structure of the amino group in 2FA and 3FA, in comparison to 4FA.

Donor–acceptor dyes with fluorine substituted phenylene spacer for dye-sensitized solar cells

A new series of organic sensitizers LJB-H, LJB-Fo and LJB-Fm with triphenylamine, 3,4-ethylenedioxythiophene plus various functionalized phenylenes, and cyanoacrylic acid as the donor, π-spacer, and anchoring group, respectively. These organic sensitizers exhibit much higher molar extinction coefficients than the parent LJ1 dye as well as reveal a remarkable fluorine substituent effect. LJB-Fm with fluoro substitution at the meta position relative to cyanoacrylic acid possesses a lower S0–S1 gap and weaker coupling with the TiO2 electrode (cf.LJB-H and LJB-Fo). Conversely, due to the resonance effect with respect to cyanoacrylic acid, the ortho-F-substituted LJB-Fo has a larger energy gap but stronger TiO2 affinity. As a result, LJB-Fo shows better DSSC performance with Jsc = 15.58 mA cm−2, Voc = 787 mV, FF = 0.67 and η = 8.22%.

ChemInform Abstract: vic-Difluorination of Fluoroalkenes with Xenon Difluoride: The Effect of Fluorine Substituents on the Reaction of Alkenes with Xenon Difluoride.

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ChemInform Abstract: Transition States for Surface-Catalyzed Chemistry

Fluorine substituent effects have been used to probe the nature of the transition states for the several elementary reaction steps occurring on metal surfaces. The reactions described include β-hydrogen elimination in adsorbed alkoxide and alkyl groups, coupling of alkyl groups, and dehalogenation of alkyl chloride and iodides. The substituent effect method can provide a connection between heterogeneous catalysis, surface science, and computational molecular simulation of surface reactions.

Selective Reduction of Carbonyl Compounds with B-Trifluoromethanesulfonyldiisopinocampheylborane in Ethyl Ether

In the previous reports, 1-4 we showed that Lewis acidity of trisubstituted borane derivatives, a series of new MeerweinPonndorf-Verley (MPV) type borane reagents, plays a role in part on their reactivity toward the reduction of carbonyl compounds: for example, the strong electron-withdrawing effect of fluorine substituent of B-trifluoroacetoxydiisopinocampheylborane (Ipc2BO2CF3) makes it much more reactive than Ipc2BOAc itself. This phenomenon strongly indicates the reaction proceeds by the activation of carbonyl group through coordination of Lewis acidic boron atom followed by hydride transfer from β-hydrogen source to the carbonyl acceptor via the six-membered transition state, quite similar to the mechanism which is generally accepted in the original MPV reaction using aluminum isopropoxide. 5 From such mechanistic point of view, we extended to design other derivative B-trifluoromethanesulfonyldiisopinocampheylborane (Ipc2BOSO2CF3). Evidently, trifluoromethanesulfonyl group is one of the strongest electron-withdrawing ones. Accordingly, we examined the general reducing characteristics of the reagent in order to understand its nature and explore its role in organic synthesis.

Fluorine substituent effects on dihydrogen bonding of transition metal hydrides

Hydrogen and dihydrogen bonding of the fluorinated alcohol (CF(3))(2)CHOH with the transition metal complex WH(CO)(2)(NO)(PMe(3))(2) has been explored by a set of four exemplary density functional theory methods that comprises the BP86, PBE, B3LYP and TPSS functionals. The hydride, nitrosyl and carbonyl ligands of the tungsten complex have been considered as sites of protonation. The main effect of fluorination is an increased dihydrogen bond strength by about 15 kJ mol(-1). The [see equation in text] dihydrogen bond is about 10 kJ mol(-1) stronger than the [W]-NOH-OR hydrogen bond. Of the four DFT methods investigated, the BP86 functional provides the most satisfying quantitative as well as qualitative agreement with experiment. The geometry of the [see equation in text] linkage is significantly influenced by secondary dispersive intermolecular bonding. Linear and bent dihydrogen bonds are separated in energy only by about 1 kJ mol(-1), and represent local minima on the corresponding energy hypersurface.

Metathesis of fluorinated olefins by ruthenium alkylidene catalysts. Fluorine substituent effects on a Ru-carbene (alkylidene) complex stability: A computational study

Cross-metathesis reaction pathways of ethylene (2a), trans-1,2-dichloro-ethylene (2b) and fluorinated olefins trans-1,2-difluoro-ethylene (2c) and tetrafluoro-ethylene (2d), with norbornene (NB) using a (1,3-diphenyl-4,5-dihydroimidazol-2-ylidene) (PCy3)CI2Ru = CHPh (I) have been studied at B3LYP/LACVP* level of theory. The calculated ΔG of reactions for olefins 2a, 2b, 2c and 2d were of 2.5, −2.0, −11.9 and −31.6 kcal/mol, respectively. The calculations show that the natural charge at a Ru center is strongly dependent on substituent nature and can be a measure of the carbene stability. The stabilization of a metallacarbene is due to the stabilization of the metal center and not a carbene carbon itself.

Electron accepting abilities of arylborane derivatives: Effect of fluorine substituents

The structures of neutral monomeric RnBH3−n and the radical anions ▪ (R=C6H5 and C6F5) have been optimized using density functional theory (B3LYP and BP86 methods) in order to evaluate their neutral-anion energy separations as indicated by their adiabatic electron affinities (EAad), vertical electron affinities (EAvert), and vertical detachment energies (VDEs). Substitution of hydrogen by C6H5 or substitution of C6H5 by C6F5 is seen to increase greatly the neutral-anion energy separations. The B–C bond rotation barriers in the neutral C6X5BH2 derivatives (X=H, F) at 8–11kcal/mol are lower than those in the corresponding anions at 15–21kcal/mol. The highest neutral-anion energy separations are found in (C6F5)3B, consistent with its strong Lewis acidity relating to its use as a cocatalyst in olefin polymerization systems.

Additivity of Ring Distortions in Halogen-Substituted Aromatics: a Gas-Phase Electron Diffraction and Computational Study

The gas-phase structures of 1,2,3-trifluorobenzene, 1,3,5-trifluorobenzene, 2,6-difluoropyridine, and 2,6-dichloropyridine have been determined using electron diffraction and computational methods. The accuracy afforded by modern experimental methods has allowed subtle trends to be identified in the geometrical parameters of the rings. Comparisons have also been made between experimental and theoretical structures. Although the effects of multiple fluorine substituents on a benzene ring are shown to be more or less additive, distortions caused by replacement of a ring carbon atom by nitrogen and by halogen substituents are not.

The effect of fluorine substituents on the polymerization mechanism of 2-methylene-1,3-dioxolane and properties of the polymer products

Perfluoro-2-methylene-1,3-dioxolane ( III) was synthesized and polymerized with an initiator, perfluoro dibenzoyl peroxide, and a white solid product III-P was quantitatively isolated. The polymer was insoluble in organic solvents including fluorinated solvents such as Fluorinert FC 75 and hexafluorobenzene, but dissolved in hexafluorobenzene by heating at around 140 °C in a sealed ampoule. The X-ray measurement showed that III-P was semi-crystalline and melted at 230 °C. The IR spectrum of III-P indicated that the polymer obtained did not show carbonyl peak and it was the vinyl addition product. When the solid product was heated above the melting temperature and pressed under 100–200 kg/cm 2, we obtained an amorphous and flexible film, which is transparent from the UV region to the near IR region. The glass transition temperature was 110 °C and refractive indexes were 1.3443, 1.3434 and 1.3373 at 633, 839 and 1544 nm, respectively. The film did not degrade in concentrated sulfuric acid and aqueous sodium hydroxide solutions even heated at 80–90 °C for 2 days. The film was thermally stable and began to decompose at 300 °C under air atmosphere.

The Effects of Fluorine and Chlorine Substituents across the Fjords of Bifluorenylidenes: Overcrowding and Stereochemistry

AbstractThe bistricyclic aromatic enes (BAEs) (E)‐ and (Z)‐1,1′‐difluorobifluorenylidene, 1,8,1′,8′‐tetrafluorobifluorenylidene, (E)‐ and (Z)‐3,3′‐difluorobifluorenylidene, 3,6,3′,6′‐tetrafluorobifluorenylidene, and their chlorinated analogues were subjected to a DFT study of overcrowding in their fjord regions. The B3LYP hybrid functional was employed to calculate energies and geometries of the twisted conformations of these BAEs. The diastereomers E11′F2 and Z11′F2 have identical twist angles (ω = 37.1°) and similar degrees of overcrowding, but differ in the degree and mode of pyramidalization, χ. In E11′F2, χ(C9) = +χ(C9′) = 7.0° (syn‐pyramidalization), while in Z11′F2, χ(C9) = –χ(C9′) = 1.0° (anti‐pyramidalization). By contrast, in E11′Cl2 and Z11′Cl2, ω = 40.6° and 42.7°, respectively. Introducing four halogen substituents results in higher twist angles: ω = 40.3° in 181′8′F4 and 52.6° in 181′8′Cl4. Surprisingly, Z11′F2 is more stable than E11′F2 (ΔH298 = –1.9 kJ/mol), whereas Z11′Cl2 is less stable than E11′Cl2 (ΔH298 = 2.2 kJ/mol). Both results are consistent with the experimental relative stabilities of these diastereomers. The unexpected stability of Z11′F2 is explained by a combination of steric and electronic effects. Calculations of Coulomb energies for point charge systems of atoms C, F, and H in the fjord regions shows stabilization of the (Z) diastereomer by –45.5 kJ/mol. The dipole–dipole interactions in the fjord region destabilize Z11′F2 by 6.4 kJ/mol relative to E11′F2. Careful examination of the NMR spectra of E11′F2 and Z11′F2 shows, in the latter, evidence of long‐range fluorine–fluorine coupling over seven bonds (11.4 Hz) and carbon–fluorine coupling over six bonds (4.8 Hz).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Effect of Fluorine Substituent on the Chitinase-catalyzed Polymerization of Sugar Oxazoline Derivatives

Abstract 6-Deoxy-6-fluoro sugar oxazoline derivatives were synthesized and evaluated their polymerizabilities with the catalysis of chitinase. The polymerizability of an N-acetyl-6-deoxy-6-fluoroglucosamine oxazoline was lower than that of non-fluorinated N-acetylglucosamine oxazoline, only providing the ring-opened hydrolyzate. The disaccharide oxazoline derivative of N,N′-diacetyl-6′-deoxy-6′-fluorochitobiose exhibited lower polymerizability with the enzyme compared to that of the non-fluorinated N,N′-diacetylchitobiose oxazoline, providing the corresponding fluorinated chitin derivative in good yields within 4 h. These results suggest that the fluorine atom-incorporation reduced the reactivity of the oxazolines.

Modern Synthetic Methods for Fluorine‐Substituted Target Molecules

AbstractFor Abstract see ChemInform Abstract in Full Text.

Modern Synthetic Methods for Fluorine‐Substituted Target Molecules

Fluorine has come to be recognized as a key element in materials science: in heat-transfer agents, liquid crystals, dyes, surfactants, plastics, elastomers, membranes, and other materials. Furthermore, many fluorine-containing biologically active agents are finding applications as pharmaceuticals and agrochemicals. Progress in synthetic fluorine chemistry has been critical to the development of these fields and has led to the invention of many novel fluorinated molecules as future drugs and materials. As a result of the electronic effects of fluorine substituents, fluorinated substrates and reagents often exhibit unusual and unique chemical properties, which often make them incompatible with established synthetic methods. Thus, the problem of how to control the unusual properties of compounds with fluorine substituents deserves much attention, so as to promote the design of facile, efficient, and environmentally benign methods for the synthesis of valuable organofluorine targets.

Fluorine-substituted unsymmetrical bent-core mesogens derived from resorcinol

Forty new bent-core compounds, unsymmetrically substituted about a central phenyl ring, were investigated for their mesomorphic properties. The effect of fluorine substituents in different positions of the phenyl rings of one of the arms of the bent-core compounds on the mesophases were examined in detail. Most of the compounds exhibit the lamellar antiferroelectric B2 mesophase. The mesophases were investigated by textural observation by polarizing microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.

Free‐radical polymerization of dioxolane and dioxane derivatives: Effect of fluorine substituents on the ring opening polymerization

AbstractPartially fluorinated and perfluorinated dioxolane and dioxane derivatives have been prepared to investigate the effect of fluorine substituents on their free‐radical polymerization products. The partially fluorinated monomer 2‐difluoromethylene‐1,3‐dioxolane (I) was readily polymerized with free‐radical initiators azobisisobutyronitrile or tri(n‐butyl)borane–air and yielded a vinyl addition product. However, the hydrocarbon analogue, 2‐methylene‐1,3‐dioxolane (II), produced as much as 50% ring opening product at 60 °C by free‐radical polymerization. 2‐Difluoromethylene‐4‐methyl‐1,3‐dioxolane (III) was synthesized and its free‐radical polymerization yielded ring opening products: 28% at 60 °C, decreasing to 7 and 4% at 0 °C and −78 °C, respectively. All the fluorine‐substituted, perfluoro‐2‐methylene‐4‐methyl‐1,3‐dioxolane (IV) produced only a vinyl addition product with perfluorobenzoylperoxide as an initiator. The six‐membered ring monomer, 2‐methylene‐1,3‐dioxane (V), caused more than 50% ring opening during free‐radical polymerization. However, the partially fluorinated analogue, 2‐difluoromethylene‐1,3‐dioxane (VI), produced only 22% ring opening product with free‐radical polymerization and the perfluorinated compound, perfluoro‐2‐methylene‐1,3‐dioxane (VII), yielded only the vinyl addition polymer. The ring opening reaction and the vinyl addition steps during the free‐radical polymerization of these monomers are competitive reactions. We discuss the reaction mechanism of the ring opening and vinyl addition polymerizations of these partially fluorinated and perfluorinated dioxolane and dioxane derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5180–5188, 2004

Temperature Dependence of Physical Constants with Varied Molecular Length and Position of Fluorine Substituents in Phenyl-bicyclohexane Core Liquid Crystals

The effects of a fluorinated substituent on physical properties of phenyl bicyclohexane liquid crystals (LCs) are reported. Temperature dependence of the physical properties for different terminals and extents of fluorine substituents were compared. Electro optic measurements suggest that the molecular length and position of fluorine strongly influence the threshold voltage and anisotropic dielectric constant. However, the resulting temperature dependences of refractive indices, order parameters and splay elastic constants indicate that the fluorine substituents cause minor differences. The effect of symmetric fluorine substituents on the benzene ring was also discussed.

Analysis of vibrational spectra of 5-fluoro, 5-chloro and 5-bromo-cytosines based on density functional theory calculations

The geometry, frequency and intensity of the vibrational bands 5-fluoro, 5-chloro and 5-bromo-cytosines (5-FC, 5-ClC and 5-BrC) were obtained by the density functional theory (DFT) calculations with Becke3–Lee–Yang–Parr (B3LYP) functional and 6-31G* basis set. The effects of fluorine, chlorine and bromine substituents on the vibrational frequencies of cytosines have been investigated. The assignments have been proposed with the aid of the results of normal coordinate analysis. The observed and the calculated spectra are found to be in good agreement.

Ionic reaction of halogens with terminal alkenes: the effect of electron-withdrawing fluorine substituents on the bonding of halonium ions.

Ionic reactions of terminal alkenes with chlorine (Cl(2)), bromine (Br(2)), and iodine monochloride (ICl) are sensitive to the alkyl substituents, and the positions and number of vinyl fluorine atoms. These perturbations influence the symmetry of the halonium ion intermediates, which can be determined by the distribution of the Markovnikov to anti-Markovnikov products. A vinyl fluorine on the number-2 carbon favors an unsymmetrical intermediate with greater charge on the number-2 carbon unless the alkyl group is electron withdrawing. A vinyl fluorine on the terminal number-1 carbon favors positive charge development on that carbon unless a resonance stabilizing group is on the number-2 carbon. The symmetry of halonium ions with vinyl fluorines on both carbons-1 and -2 depends primarily on the characteristics of the alkyl substituent. Intermediates range from open-ions with the positive charge on carbon-2, to various bridged species, to open-ions on the terminal carbon.

The effect of fluorine substitution on the structure of oxiranes and on the energetics of the oxiranylcarbinyl radical ring opening

Fluorine substituent effects on the structure of oxirane and on the kinetic behavior of oxiranylcarbinyl radicals, as determined by DFT calculations, have been found to be similar to those observed for the analogous fluorinated cyclopropylcarbinyl radical systems. A structural and energetic analysis showed that a stereoelectronic effect involving preferential interaction of the semi-occupied atomic orbital of the radical with the weaker ring bond is the major factor that contributes to the regiochemistry of the ring opening of fluorinated oxiranylcarbinyl radicals. With low and potentially zero activation barriers, 3,3-difluorooxiranylcarbinyl radical and cation undergo ring opening with CO bond cleavage and CC cleavage, respectively.