Ortho effects in mass spectrometric fragmentation processes

The mass spectra of the phenylhydrazones and 2,4-dinitrophenylhydrazones of ortho substituted benzaldehydes and acetophenones (X = I, Br, Cl, OCH₃, OH) show characteristic [M ? X]⁺ ions which allow the ortho derivatives to be distinguished from their meta and para isomers.     

Electron Diffraction and Quantum Chemical Study of the Molecular Structure of para-Methylbenzenesulfonyl Fluoride and para-Methylbenzenesulfonyl Bromide

A combined electron diffraction and mass-spectrometric experiment has been performed at 350(2) and 340(2) K, respectively, to study the molecular structure of para-methylbenzenesulfonyl fluoride and para-methylbenzenesulfonyl bromide. The electron diffraction data are analyzed in terms of r structure. Several geometrical models with different orientations of the sulfonyl halide group relative to the plane of the benzene ring are considered. The angle between the plane of the benzene ring and the plane of the S–Hal bond equals 90°, indicating that the molecules have C _s symmetry. The structural parameters of the molecules and the internal rotation barriers of the sulfonyl halide and methyl groups have been calculated by the ab initio and semiempirical quantum chemical methods. The results of calculations are compared with electron diffraction data.     

Proton and boron-11 magnetic resonance studies of some potassium tetraarylborates

Proton and boron-11 magnetic resonance spectra for several potassium para-substituted tetraarylborate compounds [KB(C₆H₄-pX)₄, where X is H, OCH₃, CH₃, Br, Cl, F, CF₃] have been obtained. The chemical shift between the centers of the AA′ and XX′ multiplets for the ring proton multiplets, relative to a reference chemical shift of 0·39 ppm for potassium tetraphenylborate, correlated with the corresponding Hammett σ values for the para-substituent. Additionally, the boron-11 chemical shifts gave a good correlation with corresponding σ values for the substituents. Electronegativities of para-substituted phenyl rings were calculated and found to be approximately 2·70 for all compounds studied. It was shown that electronic substituent effects do not greatly influence the electron density surrounding the central boron atom in the tetraarylborate ions.     

The electronic effect in supramolecular self-assembly of <Emphasis Type="Italic">para-</Emphasis>substituted tetraphenylporphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) by coordinative bonding

The supramolecular self-assembly of para-substituted tetraphenylporphyrin complexes of zinc(II), Zn(p-X)TPP, with imidazolyl-linked porphyrinatomanganese(III), Mn(p-lmBPTPP)Cl, driven by coordinative bonding has been investigated by fluorescence spectra, electrospray mass spectrometry, ¹H-n.m.r. and u.v.–vis. spectra. The association constants of the supramolecular complexes, K_c, were calculated using fluorescence spectroscopic titration data at suitable dilute concentration ranges in which the fluorescent quenching of Zn(p-X)TPP by Mn(p-ImBPTPP)Cl is a static process. The electronic effect in the supramolecular self-assembly of para-substituted . porphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) is discussed. The non-linear dependence of log K_c on the Hammett constants was found, which suggested that the electronic effect in para-substituents of tetraphenylporphyrin complexes of zinc(II) is an important, but not a sole factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes. The results indicate that the closed conformation of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complex is another important factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes.     

Substituent effects on meta-proton chemical shifts in substituted benzenes

The chemical shifts at infinite dilution and coupling constants of some meta-substituted nitrobenzenes (C₆H₄NO₂X) were determined in CDCI₃ solutions (X = CHO, OCH₃, CI, Br, NH₂, NO₂) and in CCI₄ solutions (X = OCH₃, CI, Br). Substituent effects on the chemical shift of the meta-hydrogen are analysed in terms of existing theories.     

Haloaza‐closo‐dodecaboranes

The bromo‐ and iodoaza‐closo‐dodecaboranes HNB₁₁H₁₀Hal (Hal = Br, I), MeNB₁₁H₉Br₂, and MeNB₁₁H₈Br₃ are formed from [NB₁₁H₁₁]^– and MeNB₁₁H₁₁, respectively, by electrophilic halogenation with elementary halogen in the presence of acidic catalysts. Hydrogen in para‐ or in para‐ and meta‐position with respect to the cluster‐N atom is substituted by halogen. With iodine chloride as halogenation agent, all the 11 boron bound H atoms of MeNB₁₁H₁₁ are substituted to give HNB₁₁Cl₅I₆ with iodine in the para‐ and meta‐ and chlorine in the ortho‐positions, presumably via electrophilic (I) and nucleophilic substitution (Cl). The products are characterized by their NMR spectra, the product HNB₁₁Cl₅I₆ also by crystal structure analysis.     

The kinetics of radical polymerization—XXV: Study of the radical reactivity of substituted nitrobenzenes—I

A study was made on the effect of some para- and meta-substituted nitrobenzenes on the radical polymerization of vinyl acetate. It has been shown that −CH₂X and −SO₂X type substituents have merely an inductive effect on the reactivity of nitro groups. It has also been established that the inductive effect of substituents is more intensive when they are in the para position than when in the meta position, i.e.: λ = 1·15.     

Relative Stabilities and Molecular Structures of Isomeric Dihalobenzenes. A DFT Study

The molecular structures, total energies, and other computational data of benzene, and its monoand dihalogenated derivatives (halogen = F, Cl, Br) have been studied by DFT calculations. The main aim of the study was to estimate the relative stabilities (energies) of the ortho, meta, and para isomers of the six series of dihalobenzenes investigated. The computational data show that the ortho isomers always have the highest, and the meta isomers usually, but not always, the lowest total energies. Thus, 1,2-difluorobenzene is ca. 16.6 kJ mol^–1, and 1,4-difluorobenzene 2.5 kJ mol^–1 less stable than 1,3-difluorobenzene. Among the other isomeric dihalobenzenes, the differences in stability are less pronounced. For the dibromo-, dichloro-, and bromochlorobenzenes, the para compounds are calculated to be slightly (0.2–0.4 kJ mol^–1) more stable than their meta isomers. In addition to the thermochemical aspect of the study, the computational molecular structures of the halobenzenes are compared with available experimental data and discussed in terms of the substituent-induced deformation of the ideal geometry of the benzene ring. The computational electric dipole moments, especially for the fluorine-containing compounds, compare favorably with the respective experimental (gas-phase) values.     

Potential Functions for Internal Rotation about the Csp2-O Bond and Intramolecular Interactions in p-RC6H4OCH3 Compounds

Potential functions for internal rotation about the Csp²ÄO bond in p-RC₆H₄OCH₃ compounds (R = NH₂, OCH₃, CH₃, H, F, Cl, CN, NO₂) were determined by nonempirical quantum-chemical calculations in the HF/6-31G* and MP2/6-31G* approximations with account taken of correlation energy for all electrons. The molecular conformation is planar. The height of the rotation barrier changes, depending on the electronic effect of para-substituent. Electron-donor substituents reduce while electron-acceptor substituents enhance the stability of the planar conformation. Using the natural bond orbital (NBO) approach, the nature of lone electron pairs on the methoxy oxygen atom was analyzed, and the energies for their resonance interaction with the antibonding aromatic * orbitals were determined. The effect of para-substituent on the electron density distribution over the methoxy group and on the Koopmans first ionization potentials was estimated. Geometric parameters of the molecules under study are given.     

SN1‐SN2 and SN2‐SN3 mechanistic changes revealed by transition states of the hydrolyses of benzyl chlorides and benzenesulfonyl chlorides

Hydrolysis reactions of benzyl chlorides and benzenesulfonyl chlorides were theoretically investigated with the density functional theory method, where the water molecules are explicitly considered. For the hydrolysis of benzyl chlorides (para‐Z? C₆H₄? CH₂? Cl), the number of water molecules (n) slightly influences the transition‐state (TS) structure. However, the para‐substituent (Z) of the phenyl group significantly changes the reaction process from the stepwise (S_N1) to the concerted (S_N2) pathway when it changes from the typical electron‐donating group (EDG) to the typical electron‐withdrawing one (EWG). The EDG stabilizes the carbocation (MeO? C₆H₄? CH₂⁺), which in turn makes the S_N1 mechanism more favorable and vice versa. For the hydrolysis of benzenesulfonyl chlorides (para‐Z? C₆H₄? SO₂? Cl), both the Z group and n influence the TS structure. For the combination of the large n value (n > 9) and EDG, the S_N2 mechanism was preferred. Conversely, for the combination of the small n value and EWG, the S_N3 one was more favorable. © 2014 Wiley Periodicals, Inc.     

The thermodynamic studies of the molecular interactions of methyltin(IV) tribromide with free base meso-tetraarylporphyrins

The thermodynamic parameters for the interactions of MeSnBr₃ with para- and meta-substituted meso-tetraphenylporphyrins (H₂T(4-X)PP; X=OCH₃, CH₃, H, Cl, NO₂ and H₂T(3-X)PP; X=CH₃, Cl) have been studied. The formation constants have been elucidated by using spectrophotometric titration and computer squad program data refinement. The adducts of composition 2:1 and 1:1 of MeSnBr₃ to H₂T(4-X)PP with stability constants K₁ and K₂ coexist in solution, but meta-substituted porphyrins form adducts of the composition 1:1 of MeSnBr₃ to H₂T(3-X)PP with stability constant K₁. Formation constants decrease with decreasing electron donation of para-substituted porphyrins as follow: H₂T(4-CH₃O)PP>H₂T(4-CH₃)PP>H₂TPP>H₂T(4-Cl)PP>H₂T(4-NO₂)PP. Despite the electron donation of the methyl group, H₂T(3-Cl)PP forms more stable adducts than H₂T(3-CH₃)PP with MeSnBr₃.     

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 RC₆H₄OH and RC₆H₄OCH₃ (R = n‐C₃H₇, n‐C₄H₉, n‐C₅H₁₁, n‐C₇H₁₅, n‐C₉H₁₉, n‐C₁₅H₃₁) 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 < (SBF/RER)_ortho < (SBF/RER)_para holds for the butyl phenols series. It is expected that the ‘meta effect’ described in this study enables unequivocal identification of meta isomers from ortho and para isomers not only of alkyl phenols and alkyl anisoles but also in other alkyl benzene series. Copyright © 2012 John Wiley & Sons, Ltd.     

meta-Nitration of Arenes Bearing ortho/para Directing Group(s) Using C−H Borylation

Herein, we report the meta-nitration of arenes bearing ortho/para directing group(s) using the iridium-catalyzed C−H borylation reaction followed by a newly developed copper(II)-catalyzed transformation of the crude aryl pinacol boronate esters into the corresponding nitroarenes in a one-pot fashion. This protocol allows the synthesis of meta-nitrated arenes that are tedious to prepare or require multistep synthesis using the existing methods. The reaction tolerates a wide array of ortho/para-directing groups, such as −F, −Cl, −Br, −CH₃, −Et, −iPr −OCH₃, and −OCF₃. It also provides regioselective access to the nitro derivatives of π-electron-deficient heterocycles, such as pyridine and quinoline derivatives. The application of this method is demonstrated in the late-stage modification of complex molecules and also in the gram-scale preparation of an intermediate en route to the FDA-approved drug Nilotinib. Finally, we have shown that the nitro product obtained by this strategy can also be directly converted to the aniline or hindered amine through Baran's amination protocol.     

Facile generation of platinum(IV) compounds with mixed labile moieties. Hydrogen peroxide oxidation of platinum(II) to platinum(IV) compounds

Hydrogen peroxide oxidation of platinum(II) compounds containing labile groups such as Cl, OH, and alkene moieties has been carried out and the products characterized. The reactions of [Pt^II (X)₂ (N–N)] (X = Cl, OH, X₂ = isopropylidenemalorate (ipm); N–N 2,2-dimethyl-1,3-propanediamine [(dmpda), N-isopropyl-1,3-propanediamine (ippda)] with hydrogen peroxide in an appropriate solvent at room temperature affords [Pt^IV (OH)(Y)(X)₂(N–N)] (Y = OH, OCH₃). The crystal structures of [Pt^IV(OH)(OCH₃)(Cl)₂(dmpda)]·2H₂O (P-1 bar, a = 6.339(2) Å , b = 9.861(1) Å, c = 11.561(1) Å, a = 92.078(9)°, β = 104.78(1)°, γ=100.54(1)°, V = 684.3(2) ų, Z = 2R = 0.0503) and [Pt^IV(OH)₂(ipm)(ippda)]·3H₂O (C 2/c, a = 27.275(6) Å, b=6.954(2) Å, c = 22.331(4) Å, β = 118.30(2)°, V = 3729(2) ų, Z = 8, R = 0.0345) have been solved and refined. The local geometry around the platinum(IV) atom approximates to a typical octahedral arrangement with two added groups (OH and OCH₃; OH and OH) in a transposition. The platinum(IV) compounds with potential labile moieties may be important intermediate species for further reactions.     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Small-angle neutron scattering from micelles of alkylpolyoxyethylene sulfate: Effect of chain length

Small-angle neutron scattering (SANS) data have been obtained for (i) a series of solutions of C _m H_2m+1(OCH₂–CH₂)₂SO₄Na, for m=18, 16, and 14; (ii) an approximately 0.07M solution of C₁₄H₂₉(OCH₂–CH₂)₂SO₄Na to which different amounts of NaCl were added; and (iii) a series of solutions of variable concentration of C₁₂H₂₅(OCH₂–CH₂)SO₄Na. The increase of the number of carbon atoms of the hydrocarbon chain produces a noticeable increase of the aggregation number of the micelles, while the salt tolerance decreases with increasing m. All the data can be described in terms of a monodispersed, charged, hard-spheres model interacting via a screened Coulombic potential, except the run at highest salt concentration, for which an ellipsoid model gives better results.     

New stable germylenes,stannylenes, and related compounds 7. Synthesis and structures of compounds Hal—Sn—OCH<Subscript>2</Subscript>CH<Subscript>2</Subscript>NMe<Subscript>2</Subscript> (Hal = Cl or F)

New stable divalent tin derivatives containing no bulky substituents at the metal atom, Hal—Sn— OCH₂CH₂NMe₂ (Hal = Cl or F), were synthesized, and their crystal structures were studied by X-ray diffraction. Unlike the analogous monomeric divalent germanium derivative Cl—Ge—OCH₂CH₂NMe₂, the new compounds are centrosymmetric dimers formed via two intermolecular Sn←CO coordination bonds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 259–262, February, 2007.     

C→N Migrations of the ethoxycarbonyl group in reactions of ortho-substituted aryl isocyanates with the 1,3-zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate

The reactions of meta—para-substituted aryl isocyanates with phosphorus-containing 1,3-zwitterions, which proceed with the CN migration of the CO₂Et group to form the corresponding carbamates, were extended to ortho-substituted aryl isocyanates. The influence of the steric and electronic effects of the ortho substituents in the aromatic rings of aryl isocyanates on the ease of this rearrangement is qualitatively considered.     

The role of water release from the cyclodextrin cavity in the complexation of benzoyl chlorides by dimethyl-β-cyclodextrin

The influence of temperature on the solvolysis of substituted benzoyl chlorides in the presence of dimethyl-β-cyclodextrin (DM-β-CD) was studied. Based on the influence of the DM-β-CD concentration on chemical reactivity in this process, the cyclodextrin has a catalytic effect on the solvolysis of 4-nitrobenzoyl chloride (4-NO₂) but an inhibitory effect on that of 4-methoxy-(4-MeO), 3-chloro-(3-Cl) and 3-trifluoromethyl-(3-CF₃) benzoyl chlorides. These disparate effects are related to a difference in reaction mechanism; thus, DM-β-CD catalyses associative solvolysis and inhibits dissociative solvolysis. Examining the influence of temperature on the solvolytic process allowed the stoichiometry of the host-guest complexes formed to be established. The formation constants for the complexes of meta-substituted benzoyl chlorides increased with increasing temperature. On the other hand, the equilibrium formation constants for the 1:1 host-guest complexes of para-substituted benzoyl chlorides exhibited the opposite trend. The equilibrium formation constant for 2:1 host-guest complexes for the para-substituted benzoyl chlorides increased with increasing temperature. These differences are ascribed to the release of water from the DM-β-CD cavity during the formation of the host-guest complex.