A 'meta effect' in the fragmentation reactions of ionised alkyl phenols and alkyl anisoles

The competition between benzylic cleavage (simple bond fission [SBF]) and retro-ene rearrangement (RER) from ionised ortho, meta and para RC(6) H(4) OH and RC(6) H(4) OCH(3) (R?=?n-C(3) H(7) , n-C(4) H(9) , n-C(5) H(11) , n-C(7) H(15) , n-C(9) H(19) , n-C(15) H(31) ) is examined. It is observed that the SBF/RER ratio is significantly influenced by the position of the substituent on the aromatic ring. As a rule, phenols and anisoles substituted by an alkyl group in meta position lead to more abundant methylene-2,4-cyclohexadiene cations (RER fragmentation) than their ortho and para homologues. This 'meta effect' is explained on the basis of energetic and kinetic of the two reaction channels. Quantum chemistry computations have been used to provide estimate of the thermochemistry associated with these two fragmentation routes. G3B3 calculation shows that a hydroxy or a methoxy group in the meta position destabilises the SBF and stabilises the RER product ions. Modelling of the SBF/RER intensities ratio has been performed assuming two single reaction rates for both fragmentation processes and computing them within the statistical RRKM formalism in the case of ortho, meta and para butyl phenols. It is clearly demonstrated that, combining thermochemistry and kinetics, the inequality (SBF/RER)(meta) 相似文献   

Oxygen-17 NMR Spectroscopy: Effect of Substituents on Chemical Shifts and Width Line in Ortho Substituted Nitro Benzenes

¹⁷O-NMR spectra, of ortho, meta and para substituted nitrobenzene are reported. The ¹⁷O nucleus of NO₂ group in ortho derivatives absorb at lower field that meta and para compounds. Moreover, width line of ¹⁷O resonance appears to be strongly dependent by substituent position. The ¹⁷O chemical shifts are correlated with U. V. spectra and X-ray diffraction data.     

Intensity Behaviour in the Near Ultraviolet Spectra of Chloro and Fluoro Derivatives of the Benzene Chromophore

The Interaction Vector Model (IVM) is used to understand the behaviour of the intensity of the secondary transition of chloro derivatives of the benzene chromophore, extending the work to some fluoro derivatives. These latter molecules show a surprising result: the ortho and meta interaction vectors for fluoro disubstituted molecules point in directions opposed to what has been observed in the whole preceding works.     

A Comparative Study into Two Dual Fluorescent Mechanisms via Positional Isomers of N-hydroxyarene-1,8-naphthalimides

Three isomers of hydroxy substituted N-aryl-1, 8-naphthalimides based on N-aryl naphthalic anhydride fluorophore have been synthesized. The decrease in fluorescence intensity from ortho to para substitution of hydroxy group on N-aryl reveals that para substituted isomer undergoes ESEC (Excited State with Extended Conjugation) mechanism which is proved by low quantum yield and appearance of dual emission. The ortho isomer, however, has high quantum yield and no tautomer emission, indicating ESIPT (Excited State Intramolecular Proton Transfer) mechanism is not operating. Similarly, all these isomers show strong fluorescence quenching in presence of strong H-bonding solvents like DMSO and pyridine, but there was neither the shift of emission bands nor the appearance of new bands for proton transfer to these solvents. Thus, it also indicates the absence of excited state proton transfer mechanism. Both the ortho isomer, and to a greater degree the meta isomer, showed larger quenching constants (Kapp) with pyridine than DMSO. This trend opposes the hydrogen-bond affinity for these solvents with phenol and points to a 2-point recognition interaction. In addition, a naphthalimide derivative using 2-aminoimidazole was prepared and examined for optimal positioning of a six-membered ring hydrogen bond pattern. No dual fluorescence was observed for this compound either. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

TG-FTIR技术对水氯镁石结晶热解过程的研究

水氯镁石脱水是镁资源利用的关键.其中一种重要的方法是向水氯镁石中添加助剂形成复盐及络合物脱水.通过缓慢冷却水氯镁石及盐酸苯胺的过饱和水溶液制备了水氯镁石-盐酸苯胺结晶物.通过TGDTA-FTIR联用技术分析了盐酸苯胺、水氯镁石以及盐酸苯胺-水氯镁石结晶物的热解过程,定性检测每步分解的逸出气体以推测反应过程.结果显示:盐酸苯胺在400℃以前仅发生物理变化;水氯镁石的热解分阶段进行,205℃以前发生脱去四个结晶水,205℃以后在脱水反应的同时发生水解反应生成HCl;盐酸苯胺-水氯镁石结晶物分阶段脱水、脱盐酸苯胺,整个过程没有水解现象发生,能够得到高纯度无水氯化镁.     

SERS as a probe for adsorbate orientation on silver nanoclusters

Surface‐enhanced Raman scattering (SERS) spectroscopy has been used to characterize multilayers of three isomeric aromatic compounds adsorbed on silver nanoclusters. The three structural isomers, all of which adsorb in the carboxylate form onto the silver nanoclusters, bind in two different geometries to the silver surface. Different molecular configurations correlate to differences in bonding strength of these molecules to the silver surface, which can be probed by SERS. For ortho‐hydroxybenzoic acid (salicylic acid), we observed red shifts of major SERS peaks in comparison to the normal Raman vibrations of nonadsorbed crystalline material. For this molecule the steric hindrance between the adjacent carboxylate and hydroxyl groups causes the carboxylate group to rotate from the common flat geometry of benzene substituents on surfaces and bond directly through one of the oxygen atoms to the surface. In this case, strong coordinative bonding between the carboxylate group and the metal surface causes the red shifts in the SERS peaks. For para‐, and meta‐hydroxybenzoic acid, the steric hindrance is less likely since the two functional groups are not at adjacent positions, and therefore these molecules adsorb on the silver surface in a totally flat geometry. For these molecules, in contrast to the ortho isomer, the CO₂ interacts with the surface through an extended π bond, and these molecules are physically adsorbed in the common flat position. Therefore, for the meta and para substituents, we do not observe significant red shifts in the SERS spectrum. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of Self‐Stabilized Poly(N‐(3‐Amidino)‐Aniline) Particles and their CO2‐Responsive Properties

Novel CO₂‐responsive conductive polymer particles based on poly(N‐(3‐amidino)‐aniline) (or PNAAN) are reported in this work. A CO₂‐responsive N‐(3‐amidino)‐aniline (NAAN) monomer is firstly synthesized with the pendant amidine group at the meta‐position of aniline (AN) and subsequently polymerized into the PNAAN polymer by chemical oxidation. Self‐assembly of PNAAN in turn forms the polymer particles. In the strong or weak acid media, the amidine group protonates into cationic amidinium and self‐stabilizes the PNAAN particles without the use of any stabilizers. The reaction media are found to affect the polymerization rate and self‐assembly of particles, and hence the size and size distribution of the resultant particles. The particles synthesized in strong basic media show CO₂‐responsvie properties since the H⁺ released by dissolved CO₂ (dCO₂) can protonate the amidine group into hydrophilic amidinium group and result in swelling of the PNAAN particles. Zeta‐potential measurements show the reversible change of particle surface charges in the presence and absence of dCO₂. Dynamic light scattering (DLS) measurements show the particle size linearly changed with dCO₂ concentration in the range of 5 × 10^?4 and 2.5 × 10^?2 atm. This is the first reported CO₂‐responsive polyaniline (PANI) particles for dCO₂ sensing or reversible fixation of CO₂.     

Micellar effects on aromatic nucleophilic substitution by the ANRORC mechanism. Hydrolysis of 2‐chloro‐3,5‐dinitropyridine

The hydrolysis of 2‐chloro‐3,5‐dinitropyridine by sodium hydroxide in the presence of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl) and sodium dodecyl sulfate (SDS) has been studied. The reaction follows a consecutive reaction path involving the formation of a long‐lived intermediate 3 and finally giving the product, 3,5‐dinitro 2‐pyridone 2 . The mechanism follows an addition of the nucleophile, ring opening and ring closure (ANRORC) reaction path. The rate constant was observed to be first‐order dependent on [OH^?]. The rate of reaction increased on increasing [CTABr] and, after reaching to the maxima, it started decreasing. The anionic SDS micelles inhibited the rate of hydrolysis. The results of the kinetic experiments were treated with the help of the pseudophase ion exchange model and the Menger–Portnoy model. The added salts, viz. NaBr, Na‐toluene‐4‐sulphonate, and (CH₃)₄NBr on varying [CTACl] and [SDS] inhibited the rate of reaction. The various kinetic parameters in the presence and absence of salts were determined and are reported herewith. Copyright © 2011 John Wiley & Sons, Ltd.     

Concentration and temperature dependent interaction studies using dielectric and thermodynamic methods on mixtures of anisole with o-toluidine and m-toluidine

Molecular interactions in mixtures of anisole with o-toluidine and anisole and m-toluidine have been studied at three different temperatures using the dielectric method with measurements of the static permittivity and permittivity at optical frequency. From the measured values, the Kirkwood correlation parameter, Bruggeman parameter, excess permittivity and thermodynamic excess free energy were computed for the mixtures. Positive and negative values of excess permittivity were obtained for both mixtures. The excess free energy for the anisole+o-toluidine mixture is positive at all three temperatures, whereas mixed values (positive and negative) are obtained for the anisole+m-toluidine mixture. Alignment of the dipoles in both mixtures was identified by Kirkwood factors. The investigation shows that the interaction between the components changes systematically with concentration and temperature and the change is minimum.     

The influence of electronic and structural factors on the photoinduced electron transfer in sterically strained <Emphasis Type="Italic">meso</Emphasis>-nitrophenyl-substituted porphyrins

The electronic and structural factors affecting the efficiency of the photoinduced electron transfer in meso-nitrophenyl-substituted octaethylporphyrins are theoretically analyzed by semiempirical methods of quantum chemistry. It is shown that the experimental differences between the rate constants of electron transfer associated with the change in the position of the nitro group in the meso-phenyl ring (ortho, meta, or para positions) are determined by such factors as torsional vibrations of the phenyl ring around the single C₁-C_m bond, electronic properties of the phenyl group, rotations of the nitro group around the single C-N bond, and out-ofplane deformations of the porphyrin macrocycle. It is ascertained that the matrix elements of electronic interactions and the energies of excited charge-transfer states depend substantially both on the position of the nitro group in the meso-phenyl ring and on intramolecular vibrations of the phenyl and the nitro groups. In nonpolar media, the fluorescence quenching in the compounds under study occurs mainly due to the admixture of chargetransfer excitations to the lowest S ₁ state of porphyrin. Upon increasing polarity, the main channel of deactivation of excited singlet states is direct photoinduced electron transfer either through space (the ortho position) or through a bond involving the participation of orbitals of the phenyl spacer (the meta and para positions).     

Energy transfer and spin polarization of the carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes

A series of carotenoporphyrin dyads, in which the carotenoid is covalently linked to a tetraarylporphyrin at the ortho, meta or para position of one of the meso aromatic rings, has been studied using Time-Resolved Electron Paramagnetic Resonance (TREPR) spectroscopy. In parallel, an investigation has been carried, on two different photosynthetic antenna systems, the B800–B850 complex ofR. acidophila and the LHCII complex of higher organisms. The initial spin polarization of the carotenoid triplet-state, populated indirectly by laser excitation, has been detected. It has been demonstrated that the initial polarization is not a characteristic property of the carotenoid triplet-state, as previously stated, but depends on the donor-acceptor mutual orientation. The triplet energy transfer to the carotenoid from a chlorophyll or porphyrin triplet state is discussed on the basis of the observed spin polarization.     

Computational studies of the effects of ortho‐ring and para‐ring activation on the kinetics of SNAr reactions of 1‐chloro‐2‐nitrobenzene and 1‐phenoxy‐2‐nitrobenzene with aniline

Computational studies are reported for reactions of 4‐substituted‐1‐chloro‐2,6‐dinitrobenzenes 1 , 6‐substituted‐1‐chloro‐2,4‐dinitrobenzenes 2 and some of the corresponding 1‐phenoxy derivatives 3 and 4 with aniline in the gas phase. The effects of substituent groups in the calculated energy values for reactants 1–4 , transition states structures, intermediates and products formed in the reactions between the compounds and anilines have been compared. Calculated bonds length and angles from optimized structures of the reactants were comparable with values reported for some of compounds 1–4 obtained by X‐ray crystal structures analysis. Generally, the decomposition of the Meisenheimer intermediate to the products requires more energy compared with the reactants except for when R = H. The order of stabilization of the intermediate was found to reflect the relative order of activation by substituents in the substrates. The 4‐substituted‐1‐chloro‐2,6‐dinitrobenzenes 1 and the phenoxy derivatives 3 were found to be more stable than their corresponding 6‐substituted analogues. This is an indication that the rate of nucleophilic attack at 1‐position will increase with increasing ring activation but may be reduced by steric repulsion at the reaction centre that increases in the order Cl < OPh. However, the steric hindrance to the steps involved in nucleophilic substitution by aniline is significantly increased when the substrates contain two ortho‐substituents. In most cases, the rate determining step is the decomposition of the σ‐adduct intermediate except with 1‐chloro‐2,6‐dinitrobenzenes 1 and 6‐substituted‐1‐chloro‐2,4‐dinitrobenzenes 2 , either because of reduction in ring activation or the presence of bulky ortho‐substituents in the chloro compounds 1 and 2 . Copyright © 2014 John Wiley & Sons, Ltd.     

Photochromism of new unsymmetrical isomeric diarylethenes bearing a methoxyl group

Three new unsymmetrical isomeric diarylethenes having a methoxyl substituent at ortho‐, meta‐, and para‐position of the terminal benzene ring, namely 1‐(2,5‐dimethyl‐3‐thienyl)‐2‐[2‐methyl‐5‐(2‐methoxylphenyl)‐3‐thienyl]perfluorocyclopentene ( 1o ), 1‐(2,5‐dimethyl‐3‐thienyl)‐2‐[2‐methyl‐5‐(3‐methoxylphenyl)‐3‐thienyl]perfluorocyclopentene ( 2o ), and 1‐(2,5‐dimethyl‐3‐ thienyl)‐2‐[2‐methyl‐5‐(4‐methoxylphenyl)‐3‐thienyl]perfluorocyclopentene ( 3o ), have been synthesized. The substituent position effect of methoxyl group on their properties, including photochromism and fluorescence both in hexane solution and in PMMA film, and their electrochemical properties, were investigated in detail. These diarylethenes showed good photochromism both in solution and in PMMA film. For the same photochromic diarylethene backbone, the electron‐ donating methoxyl substituent can effectively depress the cyclization quantum yields and increase the cycloreversion quantum yields compared to those of diarylethenes bearing chlorine atoms reported previously. Diarylethenes 1o – 3o showed clear fluorescent switches by photoirradiation both in hexane and in PMMA film. In addition, cyclic voltammetry tests showed that the electron‐donating methoxyl group at different position on the terminal benzene ring had a significant effect on the electrochemical properties of these isomeric diarylethenes. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrocarbon ions with triplet ground states

The N.M.R. spectra of meta dichloro and meta dibromo benzenes are analysed in the nematic phase of 4-methoxy benzylidene-4-amino-α-methyl cinnamic acid-n-propyl ester at room temperature.

The direct couplings are found to be of negative sign. The molecules orient preferentially with the aromatic plane along the direction of the magnetic field and the C ₂-symmetry axis perpendicular to it.

The relations between the various direct couplings and the inter-proton distances are reported. The ratio of the distance between the meta protons along the axis perpendicular to the C ₂ symmetry and the ortho protons is determined precisely. The other ratios could not be determined to any reasonable precision. The reasons are discussed.

The angles between the C-H bonds of the equivalent protons and the C-C bonds in both the molecules are determined on the assumption of the C-H bond lengths and the ring geometry of benzene.     

Study of the Proton Magnetic Resonance of Methoxy-Tamoxifen Towards Ortho-Substitution

The objective of the work was to study the proton magnetic resonance of derivatives of methoxytamoxifen towards ortho substitution of a trialkylstannyl-moiety and iodine. Since Iodo-methoxytamoxifen was specially needed for further biological studies in the detection and characterisation of breast tumors, it was necessary to be certain of the position of substitution (i.e. ortho to the amino ether).     

Incorporation of 2,3-Disubstituted-1,4-Naphthoquinones into the A1 Binding Site of Photosystem I Studied by EPR and ENDOR Spectroscopy

Transient electron paramagnetic resonance and pulsed electron-nuclear double resonance (ENDOR) spectra of the state $ P_{700}^{ \cdot + } A_{1}^{ \cdot - } $ in photosystem I containing a series of non-native naphthoquinones (NQs) are presented. Previous studies have shown that quinones bind to the A₁ site with only one of their carbonyl groups H-bonded to the protein and that the asymmetric H-bond produces an odd alternant distribution of the spin density within the quinone. It is known that the native phylloquinone binds with its methyl group meta and its phytyl tail ortho to the H-bonded carbonyl. Monosubstituted NQs with short alkyl chains have been found to bind preferentially with their alkyl side groups meta to the H-bonded carbonyl. The selectivity of the binding site toward methyl and short chain substituents is studied by incorporating disubstituted NQs that have a methyl group at the 2-position and a short chain at the 3-position of the quinone ring. The hyperfine couplings (hfcs) of the methyl group protons are sensitive to the spin density distribution on the quinone and are used to deduce the position of the methyl group relative to the H-bonded carbonyl. The measured methyl proton hfcs indicate that the disubstituted quinones bind exclusively with their methyl group in the meta position relative to the H-bonded carbonyl and no evidence for binding with the methyl group in the ortho position is found. The disubstituted quinones have also been chosen to study the effect of electron withdrawing substituents on the spin density distribution. When the short chain contains electronegative atoms such as sulfur or chlorine, the methyl proton hfcs of the quinone in the A₁ binding site are found to be significantly larger than those of 2-methyl-1,4-naphthoquinone and phylloquinone in the same environment. Solution ENDOR measurements of the quinone radical anions in isopropanol and density functional theory (DFT) calculations in vacuo show that this increase in the hfcs is mostly intrinsic to the quinones due to the electron-withdrawing ability of the short chain and is not a result of differences in the binding to the protein. The DFT calculations suggest that the main reason for the increased methyl proton hfcs is delocalization of the singly occupied molecular orbital onto the side chain, which leads to an increase of the spin density on the neighboring carbon, which carries methyl group.     

Magnetic resonance studies of aniline oligomers formed in the reaction of aniline with 1,1-diphenyl-2-picrylhydrazyl

Aniline oligomers, which are formed in the reaction of aniline with 1,1-diphenyl-2-picrylhydrazyl (DPPH) in methanol and chloroform as solvents, are investigated by means of magnetic resonance techniques. The electron paramagnetic resonance (EPR) spectrum of the products of the reaction of aniline with DPPH (mole ratio, 2∶1) in chloroform solution, and of aniline with DPPH (mole ratio, 1∶2) in methanol solution, were recorded as the reaction progressed, and after the reaction was finished. The spectra of the products after reaction were resolved into the spectra of two species. For the acidified methanol solution the spectrum of one of the species shows hyperfine coupling to two nitrogen atoms with a coupling constanta(2·¹⁴N)=5.8 G, in good agreement with previously reported observations for the radical cation of model aniline trimers. A species is observed in the chloroform solution witha(1·¹⁴N)=11.4 G, which suggests the presence of aniline dimers. Both solutions also show a second signal which is attributed to higher oligomer radical cations with unresolved¹⁴N hyperfine structure.¹H nuclear magnetic resonance (NMR) spectra of aniline and aniline-DPPH solutions in CDCl₃ with the peaks due to DPPHH, the product of reduction of DPPH, were observed. The¹H NMR experiments show that only 15% of the available aniline was consumed, in agreement with the theoretical calculations for the formation of polyaniline-emeraldine base salt under these conditions rather than the sole formation of dimers, which would be expected to consume 33% of the available aniline. This is probably due to formation of partially oxidized long-chain aniline oligomers as the main reaction product.     

Structural investigation of viscoelastic micellar water/CTAB/NaNO<Subscript>3</Subscript> solutions

A highly viscoelastic worm-like micellar solution is formed in hexadecyltrimethylammonium bromide (CTAB) in the presence of sodium nitrate (NaNO₃). A gradual increase in micellar length with increasing NaNO₃ was assumed from the rheological measurements where the zero-shear viscosity (η ₀) versus NaNO₃ concentration curve exhibits a maximum. However, upon increase in temperature, the viscosity decreases. Changes in the structural parameters of the micelles with addition of NaNO₃ were inferred from small angle neutron scattering measurements (SANS). The intensity of scattered neutrons in the low q region was found to increase with increasing NaNO₃ concentration. This suggests an increase in the size of the micelles and/or decrease of intermicellar interaction with increasing salt concentration. Analysis of the SANS data using prolate ellipsoidal structure and Yukawa form of interaction potential between micelles indicate that addition of NaNO₃ leads to a decrease in the surface charge of the ellipsoidal micelles which induces micellar growth. Cryo-TEM measurements support the presence of thread-like micelles in CTAB and NaNO₃.      

X-ray diffraction studies of intercalation compounds prepared from aniline salts and montmorillonite by a mechanochemical processing

Inorganic-organic intercalation compounds comprised of montmorillonite (MMT) and aniline salts with different counter anions were prepared by a mechanochemical processing. The intercalation process and the formed structure of intercalation compounds were investigated via X-ray diffraction analysis. The amounts of intercalated species were very likely dependent on the types of counter anions and increased with decreasing the size of counter anions during the mechanochemical processing. Very interestingly, much larger interlayer expansions of 1.51 nm was observed for aniline hydrofluoride AnF- and aniline hydrochloride AnCl-MMT systems in higher intercalates loading levels, suggesting that neutral guest molecules also introduce within the interlayer regions together with anilinium cations by van der Waals interactions. Judging from the larger interlayer expansions and the size of guest molecules, intercalated species are expected to prefer a tri-molecular layer arrangement with their aromatic rings perpendicular to the silicate sheets. In contrast, for aniline hydrobromide AnBr-MMT, the interlayer expansion was ca. 0.52 nm, which reveals that only anilinium cations are introduced by ion exchange and they probably adopt a vertical orientation in the interlayers. It is inferred that aniline hydroiodide AnI-MMT compounds have a heterogeneous structure containing both anilinium and sodium cations in the interlayers. Different intercalation behaviors during the mechanochemical processing strongly suggest the smaller the size of counter anions, the more guest molecules can be intercalated into the confined clay interlayers in highly ordered arrangements.