Effect Of Substituent Position Research Articles

Efficient Ligand-Free, Palladium-Catalyzed Amidocarbonylation in Ionic Liquids: Facile Synthesis of N-Acyl-α-arylglycines

A ligand-free, palladium-catalyzed amidocarbonylation reaction of aromatic aldehyde, acetamide, and CO in ionic liquids [C4mim]PF6, [C6mim]PF6, [C8mim]PF6, and [C6mim]BF4 as solvents is developed. The yields decreased in the order [C6mim]PF6 > [C8mim]PF6 > [C4mim]PF6 > [C6mim]BF4, and substrate concentration affected the catalytic activity of amidocarbonylation. The excellent yield with up to 98% in amidocarbonylation of benzaldehyde was obtained using 15 mol% LiBr · H2O and 6 mol% H2SO4 at 80 °C. This reaction could proceed smoothly, resulting in several functionalized ortho-, meta-, and para-substituted N-acyl-α-phenylglycines in moderate to good yields, and o-tolualdehyde and m-tolualdehyde as substrates were amidocarbonylated for the first time in [C6mim]PF6. A significant dependence of product yield on both substituent position and electronic effect of aromatic aldehyde was observed. The ligand-free synthetic method and convenient separation of the products highlighted the versatility of this newly developed methodology.

Self-Assembly of Discotic Mesogens in Solution and in Liquid Crystalline Phases: Effects of Substituent Position and Hydrogen Bonding

The effects of functional group position on the phase behavior of discotic mesogens was examined for a series of dibenzophenazine derivatives bearing a carboxylic acid, methyl carboxylate, or nitro group. In all cases, changing the position of the group from the "top" to the "side" of the aromatic core led to dramatic differences in the phase behavior, both in terms of the stability of the liquid crystalline phases as well as the types of mesophases formed. For the non-hydrogen bonding ester and nitro derivatives, moving the substituent to the side of the core led to a lowering of the clearing temperatures or loss of liquid crystallinity. Carboxylic acid derivatives exhibit broad mesophases irrespective of the position of the acid group, but mesogens bearing this group on the side of the core exclusively form Col(h) phases, whereas those with an acid group on the top of the core exhibit more varied mesomorphism, with the formation of Col(h), Col(r), and nematic phases. Contrary to expectations, the presence of a carboxylic acid group on the side of the core does not appear to lead to the formation of dimeric structures in the liquid crystalline phase, although the columnar structures appear to be stabilized by intermolecular hydrogen bonding along the columns. These derivatives also form pi-stacked dimers in solution; the structure of these dimers are consistent with the proposed structure of the columnar phases.

Carbon Dioxide Solubility Enhancement through Silicone Functionalization: “CO2-philic” Oligo(dimethylsiloxane)-substituted Diphosphonates*

Carbon dioxide has received significant attention as a potential environmentally benign medium to replace hazardous organic compounds, but is a relatively poor solvent. The addition of siloxane substituents provides an attractive and inexpensive means to solubilize a wide variety of compounds in CO2. By synthesizing and testing a family of gem-diphosphonate ligands that have been rendered CO2-philic by incorporation of a number of related, discrete dimethylsiloxane oligomers, we show that small variations in substituents have a significant effect on the CO2-philicity of the ligand. To our knowledge, this is the first systematic study of the effect of siloxane substituent size, branching, and position on the affinity of a ligand for CO2. In addition, we present a general approach to the preparation of novel gem-diphosphonate ligands.

Substituent position effect on the properties of new unsymmetrical isomeric diarylethenes having a chlorine atom

Three new unsymmetrical photochromic diarylethenes bearing a chlorine atom at para-, meta- and ortho-position of one terminal benzene ring, namely {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(4-chlorophenyl)-3-thienyl]}perfluorocyclopentene ( para 1o), {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(3-chlorophenyl)-3-thienyl]}perfluorocyclopentene ( meta 2o), and {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(2-chlorophenyl) -3-thienyl]}perfluorocyclopentene ( ortho 3o), have been synthesized. The substituent position effect on their properties, including photochromism, fluorescence both in solution and in PMMA amorphous film and their electrochemical properties were investigated in detail. The results elucidated that the chlorine atom and its substituent position had a remarkable effect on the absorption characteristics, photochromic reactivity, fluorescence, as well as the electrochemical performances of these diarylethene compounds. For diarylethenes 1, 2 and 3, the cycloreversion quantum yields were gradually increased when the chlorine atom was attached to the para-, meta- and ortho-positions of the one terminal benzene rings; but their molar absorption coefficients both of their open-ring and closed-ring isomers were remarkably decreased. The fluorescent properties of para-substituted diarylethene embedded in poly(methyl methacylate) (PMMA) amorphous film showed good fluorescent switches (quenched to 28%). Furthermore, the cyclic voltammograms experiments elucidated that the electrochemical properties of these diarylethene derivatives were also remarkably dependent on the chlorine atom position effect, which may be attributed to the different electron-inducing ability and steric effect when the chlorine atom was substituted on the different position of the terminal benzene ring.

PHOTOCHROMIC KINETICS OF ASYMMETRICAL DIARYLETHENES IN DIFFERENT SOLVENTS AND IN PMMA FILMS

Three new asymmetric photochromic diarylethenes bearing fluorine atoms at the ortho-, meta-, or para-position of one terminal phenyl group were synthesized, and their photochromism and kinetics of the photochromic cyclization/cycloreversion both in different solvents and in PMMA films were investigated. The results showed that the cyclization/cycloreversion process of these compounds were determined to be zeroth/first order reaction, and the reaction rates (k) were obtained from the slope of every line. The substituent position effect on the cycloreversion process of the three compounds was remarkable and the solvent polarity enhanced this effect. The values of reaction rates in PMMA films were quite different from those in solvents indicating that the kinetics processes of the three compounds taking place in PMMA films differs from the same processes occurring in common solvent.

Electron-withdrawing substituent position effect on the optoelectronic properties of new photochromic diarylethenes

Three new photochromic diarylethenes bearing cyano groups at the ortho-, meta-, or para-positions of both terminal phenyl rings, namely 1,2-bis(2-methyl-5-(2-cyanophenyl)-3-thienyl)perfluorocyclopentene (1a), 1,2-bis(2-methyl-5-(3-cyanophenyl)-3-thienyl)perfluorocyclopentene (2a), and 1,2-bis(2-methyl-5-(4-cyanophenyl)-3-thienyl)perfluorocyclopentene (3a), have been synthesized. The substituent position effects on their optoelectronic properties, including photochromism, fluorescence and electrochemical properties in solution, were investigated systematically. The molar absorption coefficient (ε = 7.48 × 104 L mol− 1 cm− 1), the absorption maxima and the quantum cyclization yield (Φ 0 − c = 0.53) of 3a are the biggest while its cycloreversion quantum yield (Φ c − 0 = 0.004) is the smallest. In hexane, the fluorescent emission peaks of diarylethenes 1a, 2a and 3a showed a bathochromic shift upon increasing concentration. The oxidations of diarylethenes 1a, 2a and 3a are initiated at 1.85, 1.58 and 1.58 V, respectively, which are higher than those of their closed-ring forms 1b, 2b and 3b (1.61, 1.43 and 1.49 V, respectively). The results indicate that the optoelectronic features of diarylethenes 1, 2 and 3 are distinctly different, which may be attributed to the different electron-withdrawing ability and steric effect of cyano groups with different substituted positions.

Synthesis and chlorine atom position effect on the properties of unsymmetrical photochromic diarylethenes

Unsymmetrical photochromic diarylethenes 1o– 4o have been synthesized, which diarylethenes 1o– 3o have a chlorine atom at ortho-, meta- and para-position of the terminal phenyl ring, respectively. The substituent position effect of chlorine atom on their properties, including photochromism both in solution and in the single crystalline phase and their electrochemical properties were investigated in detail. The results elucidated that the chlorine atom and its substituted position had significantly affected on the absorption characteristics, photochromic reactivity as well as the electrochemical performances of these diarylethene compounds. When the chlorine atom was introduced into the phenyl ring of these diarylethene systems, the cycloreversion quantum yields were effectively depressed; but, the molar absorption coefficients of the open-ring isomer and the differences of oxidation potential onsets between the open- and closed-ring isomers of these diarylethenes were significantly increased. Moreover, the position of the chlorine atom had also influenced evidently the above optical and electrochemical features.

Substituent effect on the amino–imino tautomerism of aminothiazoles

The effect of type and substituent position on the conformational, structure and amino–imino tautomerism of aminothiazoles in the gas, water and carbon tetrachloride phases has been studied using the B3LYP/6-311++G(d,p) and MP2(full)/6-311++G(d,p) levels. They showed that the amino form is more stable than the imino in the three phases. This was in a good agreement with the experimental data. The electron donating group (–CH 3); positioned at four and five, increased the amount of imino form. Despite the greater substituent stability of the imino, the amino tautomer was found to be the predominant species. The electron-withdrawing group attached to the exocyclic nitrogen increased the acidity of exocyclic –NH group, thus facilitating the hydrogen transfer to the endocyclic nitrogen atom. The total energy of the imino form was lower than that of the amino, exhibiting the coexistence of the two structures in the gas phase. The tautomerization became spontaneous in solutions at room temperature and the imino was the predominate.

Substituent position effect on the properties of isomeric photochromic diarylethenes bearing chlorine atoms

Three new isomeric photochromic diarylethenes, namely 1,2-bis[2-methyl-5-(4-chlorophenyl)-3-thienyl]perfluorocyclopentene ( 1o), 1,2-bis[2-methyl-5-(3-chlorophenyl)-3-thienyl]perfluorocyclopentene ( 2o), and 1,2-bis[2-methyl-5-(2-chlorophenyl)-3-thienyl]perfluorocyclopentene ( 3o) which bear two chlorine atoms at the para-, meta-, and ortho-position of both terminal phenyl groups, have been synthesized. The substituent position effect of chlorine atoms on their optoelectronic properties, including photochromic behavior and fluorescence, both in solution and in PMMA amorphous film, and electrochemical properties were investigated in detail. The results elucidated that the chlorine atoms and their substituent positions had a significant effect on the optoelectronic properties of these compounds. These diarylethene derivatives bearing two chlorine atoms have shown good photochromic behavior and fluorescent switching both in solution and in PMMA film. For diarylethenes 1– 3, the cycloreversion quantum yields were gradually increased when the chlorine atom was attached to the para-, meta- and ortho-positions of the two terminal benzene rings; but, their absorption maxima, cyclization quantum yields and the molar absorption coefficients both of their open-ring and closed-ring isomers were remarkably decreased one by one. Furthermore, the clear oxidation waves of diarylethenes 1c, 2c and 3c were observed at 1.01, 0.92 and 0.98 V by performing the cyclic voltammograms experiments.

Discotic liquid crystals of transition metal complexes 38†: peripheral chain substituent position effect on columnar mesophase and stacking structures of novel phthalocyanine-based liquid crystals

In order to clarify the peripheral chain substitution position effect on columnar mesophase and stacking structures, we have synthesized three novel series of discotic liquid crystals (1-3) having octakis(phenoxy)phthalocyaninato copper(II) as a central core and one peripheral chain at the para position (1), meta position (2) or ortho position (3) of each phenoxy group, and three more novel series of discotic liquid crystals (4-6) having the same central core and two peripheral chains at para and meta positions (4), meta and meta positions (5) or ortho and meta positions (6) of each phenoxy group. Their columnar mesophase and stacking structures were investigated with a polarizing optical microscope, a differential scanning calorimeter and a temperature-dependent X-ray diffractometer. According to the results, their columnar mesophase and stacking structures strongly depended on the peripheral chain substitution positions and the number of peripheral chains. Derivatives 3 and 5 are viscous isotropic liquid at room temperature. Derivatives 1, 2, 4 and 6 exhibit various kinds of columnar mesophases: 1 Colhd; 2 Colhd and Colho; 4 Colhd, Colrd(P21/a), Coltet.d and Cub ( Pn [ three bar ] m ); 6 Colhd, Colrd(P21/a) and Colrd(X). Moreover, derivatives 1, 4 and 6 exhibit disordered columnar mesophases. However, derivative 2 only exhibits an ordered columnar mesophase and its X-ray diffraction pattern shows a sharp reflection corresponding to a very short intracolumnar stacking distance of 3.33 Å. Thus, we can drastically change the mesophase and stacking structures by the peripheral chain substitution positions and the number of peripheral chains at each phenoxy group. This is a new way of controlling mesomorphic structure.

A HeI photoelectron spectroscopy and theoretical study of 2,6-dichloropyrazine, 2,3-dichloropyrazine, 4,6-dichloropyrimidine and 3,6-dichloropyridazine

The electronic structures of C 4H 2Cl 2N 2 isomers have been studied by HeI photoelectron spectroscopy (PES) combined with the outer valence Green’s function (OVGF) calculations at 6-311++G(d,p) basis sets. The vertical first ionization potentials for 2,6-dichloropyrazine, 2,3-dichloropyrazine, 4,6-dichloropyrimidine and 3,6-dichloropyridazine are determined to be 9.93, 9.89, 10.45 and 10.07 eV, respectively, and the PE spectra were assigned based on molecular orbital analysis and by comparison with related compounds. The effects of chlorine substituent and different positions of nitrogen atoms in these C 4H 2Cl 2N 2 isomers have been carefully analyzed by comparing the C 4H 2Cl 2N 2 isomers with their matrixes (pyrazine, pyridazine, pyrimidine). The inductive effect of chlorine substituent leads to the stabilization of the nitrogen lone pair orbitals. The resonance effect predominates over the inductive effect, and the consequence is the destabilization of the π orbitals. Owing to the different positions, the effects of nitrogen atoms are different and lead to the different sequence of π orbitals.

Substituent position effect on the optoelectronic properties of photochromic diarylethenes

Photochromic diarylethenes bearing fluorine atoms at the ortho-, meta-, or para-position of both terminal phenyl rings have been synthesized. Effect of the substituent positions on their optoelectronic properties, including photochromism in solution, fluorescence, and electrochemical properties were investigated for the first time. The results indicated that the position of the fluorine substituent had remarkable impacts on molar absorption coefficient of the closed-ring forms of diarylethenes, quantum yields of the cyclization and cycloreversion reactions, fluorescence intensity, as well as the oxidation potential.

Preparation and Nonlinear Optical Properties of Inorganic−Organic Hybrid Films with Various Substituents on Chromophores

Four kinds of hydroxy-ended azobenzene-type chromophores containing different substituent groups as electron donor or electron acceptor were synthesized and further reacted with 3-isocyanatopropyltriethoxysilane (ICTES) to give alkoxysilane dyes via a urethane reaction. Following a sol-gel process of the alkoxysilane dyes, the inorganic-organic hybrid nonlinear optical (NLO) films were successfully prepared. Molecular structures of the resultant films were confirmed by elemental analysis, FTIR, and 1H NMR. The betaCT mu(g) values of the chromophores were evaluated by a solvatochromic method, and the second harmonic coefficients (d33) of the hybrid films were measured by in situ second harmonic generation (SHG) measurement. The hybrid films exhibited large optical nonlinearity and full transparency in the visible range. The effects of substituent group and position on betaCT mu(g) values of the chromophores and d33 values of the films were also discussed.

Bacterial Monooxygenase Mediated Preparation of Nonracemic Chiral Oxiranes: Study of the Effects of Substituent Nature and Position.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Effect of substituent position on the ethylene polymerization by Fe(II) and Co(II) pyridyl bis-imine catalysts

Polymerizations and oligomerizations of ethylene by using a series of bis(imino)pyridyl Co(II) and Fe(II) complexes {[(2-ArNC(Me)) 2C 5H 3N]MCl 2} (Ar=2,6-C 6H 3Me 2, 1; 2,5-C 6H 3Me 2, 2; 2,4-C 6H 3Me 2, 3; 2,3-C 6H 3Me 2, 4; MCo, a; Fe, b) bearing two methyl substituents on each imine aryl group are reported. These complexes, when activated with methylaluminoxane in aromatic or aliphatic hydrocarbon solvents, oligomerize or polymerize ethylene to α-olefins or high polymers with exceptionally high activities and selectivities. The activities and selectivities to α-olefins or high polymers are dependent on the catalyst structure and the type of metal. The steric bulk around the metal center is key to retarding chain transfer to obtain high molecular weight polyethylene.

Bacterial monooxygenase mediated preparation of nonracemic chiral oxiranes: study of the effects of substituent nature and position

Monooxygenation of styrene derivatives using recombinant E. coli biocatalyst is an efficient way to prepare the corresponding oxiranes. The electronic and geometric effects of the ring substituents are described and show the relaxed specificity of the enzyme and its high stereoselectivity.

Dications of Fluorenylidenes: The Effect of Substituent Electronegativity and Position on the Antiaromaticity of Substituted Tetrabenzo[5.5]fulvalene Dications.

Oxidation of 3,6-disubstituted tetrabenzo[5.5]fulvalenes by SbF5 results in the formation of dications that behave like two antiaromatic fluorenyl cations connected by a single bond. Both fluorenyl systems exhibit the paratropic shifts and nucleus independent chemical shifts (NICS) characteristic of antiaromatic species. Comparison with analogous 2,7-disubstituted tetrabenzo[5.5]fulvalenes reveals that the antiaromaticity of the substituted ring system can be altered substantially by changes in the placement of the substituents, possibly due to changes in the delocalization of charge in the system. Substituents in the 3,6-position decrease the antiaromaticity because of the increase in the benzylic resonance compared to 2,7-substituents.

Dications of fluorenylidenes. The effect of substituent electronegativity and position on the antiaromaticity of substituted tetrabenzo[5.5]fulvalene dications.

Oxidation of 3,6-disubstituted tetrabenzo[5.5]fulvalenes by SbF(5) results in the formation of dications that behave like two antiaromatic fluorenyl cations connected by a single bond. Both fluorenyl systems exhibit the paratropic shifts and nucleus independent chemical shifts (NICS) characteristic of antiaromatic species. Comparison with analogous 2,7-disubstituted tetrabenzo[5.5]fulvalenes reveals that the antiaromaticity of the substituted ring system can be altered substantially by changes in the placement of the substituents, possibly due to changes in the delocalization of charge in the system. Substituents in the 3,6-position decrease the antiaromaticity because of the increase in the benzylic resonance compared to 2,7-substituents.

Alkoxycarbonyl substituted ruthenium mono(bipyridine) complexes: steric effects of the bipyridine substituents

Mono(bipyridine) complexes of ruthenium ( n, n′-L 2-2,2′-bpy)Ru(CO) 2Cl 2 ( n=3, 4, 5, or 6; L=CO(O)Me or CO(O)Et) were synthesised and structurally characterised. The steric effects of the substituents L on the geometry and the energetics of the compounds were studied using both experimental and theoretical methods to clarify the effect of substituent position on complex behaviour and electrochemical properties. Calculations were carried out with the density functional hybrid B3PW91 method. The position of the substituent was found to strongly effect the geometry and the energy of the mono(bipyridine) complexes. Alkoxycarbonyl substituents at 3,3′- and 6,6′-positions caused strong structural distortion of the complexes. The strain caused by 6,6′-substituents was readily relaxed forming new chelating complex with tridentate ligand coordination. Varying the bipyridine substituent position also caused changes in the electrochemical properties of the compounds reflected by the variations in the HOMO–LUMO energy gap. Ligand modifications caused by changing the substituent locations offer possibilities to design complexes with the required structural or electrochemical properties.

Synthesis, characterization, and imaging performance of a new class of macrocyclic hepatobiliary MR contrast agents.

To investigate the effect of substituent lipophilicity, substituent position, and overall charge on the hepatobiliary clearance and tolerance of a series of aromatic ring-containing macrocyclic Gd chelates to select a candidate compound for evaluation as a hepatobiliary imaging agent. Hepatobiliary clearance was studied in rats. Tissue distribution and tolerance were studied in mice. Imaging was performed in cats, rabbits, and Rhesus monkeys using T1-weighted pulse sequences or T1-weighted breath-hold pulse sequences. All the compounds were excreted bimodally. Gd-2,5-BPA-DO3A (15d) was found to have the optimal combination of hepatobiliary clearance (47% in rats, 29% in mice) and tolerance (minimum lethal dose 5.0 mmol/kg). Initial imaging studies in cats demonstrated the feasibility of Gd-2,5-BPA-DO3A for hepatic imaging. In rabbits with implanted VX-2 adenocarcinoma as a model for metastatic liver disease, Gd-2,5-BPA-DO3A provided sustained hepatic signal intensity (SI) enhancement and lesion conspicuity over a 120-minute imaging time course. In Rhesus monkeys with normal liver function, Gd-2,5-BPA-DO3A afforded sustained hepatic SI enhancement and a time-dependent increase in gallbladder SI over the entire 90-minute imaging time course. Gd-2,5-BPA-DO3A provides dramatic and sustained SI enhancement of hepatic tissue in cats, rabbits, and Rhesus monkeys that was superior in all respects to the extracellular space MRI agent, Gd-HP-DO3A, that was employed as a control.