The o-, m-, and p-benzyne radical cations: a theoretical study

On the basis of the CASPT2 (multiconfigurational second-order perturbation theory) geometry optimization calculations, the ground states of the o-C(6)H(4)(+) (C(2v)), m-C(6)H(4)(+) (C(2v)), and p-C(6)H(4)(+) (D(2h)) radical cations were determined to be 1 (2)B(1), 1 (2)A(2), and 1 (2)B(1u), respectively. For o-C(6)H(4)(+) and m-C(6)H(4)(+), the first excited states (1 (2)A(2) and 1 (2)A(1), respectively) lie very close to the respective ground states. The small distance value of 1.419 A between the two dehydrocarbons in the ground-state geometry of m-C(6)H(4)(+) indicates that there is a real chemical bond between the two dehydrocarbons (the distance in the 1 (2)A(1) geometry of m-C(6)H(4)(+) is very long as in the m-C(6)H(4) molecule). The (U)B3LYP isotropic proton hfcc (hyperfine coupling constant) calculation results imply that the ground and first excited states of o-C(6)H(4)(+) will have similar ESR spectrum patterns while the ground and first excited states of m-C(6)H(4)(+) will have completely different ESR spectrum patterns.     

Theoretical investigation on o-, m-, and p-chlorotoluene photodissociations at 193 and 266 nm

Photodissociations of the o-, m-, and p-chlorotoluene at 193 and 266 nm were investigated by ab initio calculations with and without spin-orbit interaction. The experimentally observed photodissociation channels were clearly assigned by multistate second order multiconfigurational perturbation theory (MS-CASPT2) calculated potential energy curves. The dissociation products with spin-orbit-coupled states of Cl*(2P1/2) and Cl(2P3/2) were identified by MS-CASPT2 in conjunction with spin-orbit interaction through complete active space state interaction (MS-CASPT2/CASSI-SO) calculations. The effects of methyl rotation and substituent on the photodissociation mechanism were discussed in detail.     

Collision induced dissociations of radical cations

The collision induced dissociation spectra of ions generated by ionization or fragmentation of various samples reveal at least five non-decomposing structures. In contrast, the kinetic energy release measurements for the loss of carbon monoxide from the metastable ions are in agreement with the occurrence of a common reactive species. Isomerization into an ‘α,β-unsaturated aldehyde-like’ structure prior to fragmentation is proposed to accommodate these collision induced dissociation and mass analysed ion kinetic energy data. Some resuts suggest also that carbon monoxide loss from the phenol molecular ion may not occur via the cyclohexadienone tautomer.     

Formation and decomposition of distonic o-, m-, and p-benzyne radical cations from photolysis of Mg(+)(o-, m-, p-C(6)H(4)F(2))

Distonic o-, m-, and p-benzyne radical cations (1-3) have been generated by a novel photolysis reaction of mass-selected Mg(+)-difluorobenzene complexes. The energy required for the formation of these radical cations is within 2.2 eV. The formation of o-benzyne cation is most facile. The benzyne radical cations dissociate further to yield ethyne and 1,3-butadiyne radical cation as major products given a sufficient amount of energy. The whole process involves only a single photon, and is very efficient. The calculated threshold for the formation of 1,3-butadiyne radical cation from Mg(+)(o-C(6)H(4)F(2)) is about 4.6 eV, quite comparable with the experimental estimate.     

Efficient unimolecular deprotonation of aniline radical cations

[reaction: see text] Deprotonation of the radical cations of aromatic amines, such as anilines, generally occurs much more slowly than other fragmentation reactions. Here we report a stereoelectronic effect involving twisting of the anilino group out of the plane of the benzene ring that results in a significantly increased rate of reactivity toward deprotonation. Quantitative studies of the rate constants for deprotonation as a function of aniline radical cation pKa (Br?nsted plots) demonstrate that the effect is not simply due to a change in the reaction thermodynamics. By combining this stereoelectronic effect with covalent attachment of carboxylate as a base, aniline radical cations that undergo unimolecular deprotonation with rate constants as high as 10(8) s(-1), even in unfavorable protic media, are described.     

Kinetics for tautomerizations and dissociations of triglycine radical cations

Fragmentations of tautomers of the α-centered radical triglycine radical cation, [GGG^•]⁺, [GG^•G]⁺, and [G^•GG]⁺, are charge-driven, giving b-type ions; these are processes that are facilitated by a mobile proton, as in the fragmentation of protonated triglycine (Rodriquez, C. F. et al. J. Am. Chem. Soc. 2001, 123, 3006–3012). By contrast, radical centers are less mobile. Two mechanisms have been examined theoretically utilizing density functional theory and Rice-Ramsperger-Kassel-Marcus modeling: (1) a direct hydrogen-atom migration between two α-carbons, and (2) a two-step proton migration involving canonical [GGG]^•+ as an intermediate. Predictions employing the latter mechanism are in good agreement with results of recent CID experiments (Chu, I. K. et al. J. Am. Chem. Soc. 2008, 130, 7862–7872).     

Vibrational spectroscopic study of o-, m- and p-hydroxybenzylideneaminoantipyrines

Three structurally similar antipyrine derivatives of o-hydroxybenzylideneaminoantipyrine (o-HBAP), m-hydroxybenzylideneaminoantipyrine (m-HBAP) and p-hydroxybenzylideneaminoantipyrine (p-HBAP) were characterized by FT-IR, FT-Raman experimental techniques and density functional theoretical (DFT) calculations. The comparisons between the calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The optimized molecular geometries agree well with the corresponding experimental values by comparing with the XRD data. The comparisons and assignments of the vibrational frequencies indicate that the experimental spectra also coincide satisfactorily with those of theoretically simulated spectrograms except the hydrogen-bond coupling infrared vibrations, and compounds can be distinguished by the IR and Raman spectra due to the differences of the hydroxyl-substituted positions and molecular packing, and the strong Raman scattering activities of the compounds are tightly relative to the molecular conjugative moieties linked through the Schiff base imines. The thermodynamic functions and their correlations with temperatures were also obtained from the theoretical harmonic frequencies.     

Zur Unterscheidung von o-, m- und p-Phenylendiamin

Ohne Zusammenfassung     

Magnetic properties and aromaticity of o-, m-, and p-benzyne

The relative aromaticities of the three singlet benzyne isomers, 1,2-, 1,3-, and 1,4-didehydrobenzenes have been evaluated with a series of aromaticity indicators, including magnetic susceptibility anisotropies and exaltations, nucleus-independent chemical shifts (NICS), and aromatic stabilization energies (all evaluated at the DFT level), as well as valence-bond Pauling resonance energies. Most of the criteria point to the o-benzyne相似文献   

Reactions of radical cations of acetals: Evidence for unimolecular decomposition

The thermal and photochemical reactions of the methylal radical cation /I/ in freon matrices were studied using selective deuteration for elucidating the structure of the resulting species. /I/ has been shown to decay by unimolecular reaction upon heating to 140 K as well as upon photolysis in CFCl₃ matrix and the product of decay has been assumed to be the complex of formaldehyde radical cation with CFCl₃. Such decay reaction has been demonstrated for 1,3-dioxolan radical cation as well.     

Relativistic multireference calculation of photodissociation of o-, m-, and p-bromofluorobenzene

Quantum chemical calculations with relativistic effects were performed on the photodissociation of o-, m-, and p-bromofluorobenzene (o-, m-, and p-BrFPh) at 266 nm. The method of multistate second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space state interaction was employed to calculate the potential energy curves for the ground and low-lying excited states of o-, m-, and p-BrFPh along their photodissociation reaction coordinates. The dissociation mechanisms with products of Br((2)P(3∕2)) and Br(?)((2)P(1∕2)) states were clarified with the computed potential energy curves and the surface crossings. The current calculations augmented previous theoretical investigations by including relativistic effects and resolved some differences of experimental assignment regarding the dissociation channels of o-, m-, and p-BrFPh.     

Studies of adsorption equilibria and kinetics of o-, m-, p-nitro- and chlorophenols on microporous carbons from aqueous solutions

The studies of adsorption of o-, m-, and p-nitrophenols and chlorophenols from aqueous solutions on microporous activated carbon are presented. The adsorption isotherms were measured at different temperatures: 288, 298, 308 and 318 K. The thermal analysis was applied in order to find the differences in solute interactions with adsorbent surface. The kinetic dependences were measured and the relations between position of adsorbate functional groups and adsorption rate were discussed. The adsorption data are analyzed in terms of the theory of physical adsorption on energetically non-homogeneous solids. The relations between the adsorbate structure and adsorption effectiveness, and the influence of temperature are discussed.     

Zur gaschromatographischen Analyse von o-, m- und p-Chloronitrobenzol

Ohne Zusammenfassung     

Effect of hydrogen bonding on the polymerization of N-(o-,m-, and p-methoxyphenyl)- and N-(o-,m-, and p-ethoxyphenyl)-methacrylamides

Summary Study of the rates of polymerization of N-(o-, m-, and p-methoxyphenyl)- and N-(o-, m-, and p-ethoxy-phenyl)methacrylamides showed that the ortho isomers of these compounds, in which there is no association between the molecules, polymerize much more rapidly than their meta and para isomers, the molecules of which are associated through hydrogen bonds.     

离子色谱法分析邻,间,对硝基苯酚

建立了一种分析邻，间，对硝基苯酚的离子色谱分析体系，选用亚硝酸钠溶液作为淋洗液，紫外检测波长２５４ｎｍ能很好的分析硝基苯酚异构体，检测限低于１０＾－４ｇ／Ｌ。     

镁铝类水滑石对邻、间、对甲基苯酚的吸附

采用液相非稳态共沉淀法制备了镁铝类水滑石（Mg-Al HTlc）,并研究了邻、间和对甲基苯酚在Mg-Al HTlc上的吸附行为。 结果表明,邻、间和对甲基苯酚在Mg-Al HTlc上的吸附等温方程均符合Freundlich吸附等温式;吸附动力学均符合准二级动力学方程;在实验范围内,Mg-Al HTlc对三者的吸附量为：对甲基苯酚＞邻甲基苯酚＞间甲基苯酚;在pH值5.00~13.00范围内,三者的吸附量均随pH值的增加先增大后减小、随温度升高和电解质（NaCl）浓度的增大而增大。 探讨了吸附机理和苯环上甲基取代基位置对吸附的影响。