The formation of highly excited H in the reaction H2+(v) + H2 → H + H

A quasiclassical trajectory surface hopping method has been used to study H(v) + H₂ → H + H for v = 0, 3, 7, 10, 13, and 17 with an emphasis on determining the H internal energy and angular momentum distributions for high v. For v = 13 and 17, significant cross sections are found for producing H at energies above its dissociation energy. An average metastable H lifetime of 11.5 ps for v = 13 and 4.7 ps for v = 17 is found, but there is also a much longer lived component to the lifetime distributions that is more important for v = 13 than for v = 17. Some of the longer lived metastables correspond to high angular momentum orbiting states of H, but other sources of metastability are also present.     

Syntheses of 1,3,6,8,10,11,14-heptaazapentaphene-2,4,7,9(14H,3H,8H, -11H)-tetrones (angular mixed flavins), 1,3,5,6,8,10,11,14-octaazapentaphene-2,4,7,9(14H,3H,8H,11H)-tetrones (angular doubled flavins), and their related compounds

Cyclization of N, N′-dialkyl-N-(3-methyluracil-6-yl)-N′-(5-nitro-3-methyluracil-6-yl)- p-phenylenediamines with the Vilsmeier reagent gives the corresponding 1,3,6,8,10,11,14-heptaazapentaphene-2,4,7,9-(14H,3H,8H,-11H) -tetrones (angular mixed flavins) 2. Cyclization of N, N′-di(5-nitro-3-methyluracil-6-yl)-p-phenylenedi-amines with the Vilsmeier reagent gives the corresponding 1,3,5,6,8,10,11,14-octaazapentaphene-2,4,7,9-(14H,3H,8H,11H)-tetrones (angular doubled flavins) 11 along with the angular mixed flavins 2.     

Syntheses of 1,3,8,10,12-pentazanaphthacene-2,4,7,9-(12H,3H,8H,10H)-tetraones (linear pyrimidine-fused 5-deazaflavins), 1,3,6,8,12-pentazabenz[a]anthracene-2,4,7,9(12H,3H,6H,8H)-tetraones(bent pyrimidine-fused 5-deazaflavins), and their flavin analogs

1,3,8,10,12-Pentazanaphthacene-2,4,7,9(12H,3H,8H,10H)-tetraones (linear pyrimidine-fused 5-deazaflavins) and 1,3,6,8,12-pentazabenz[a]anthracene-2,4,7,9(12H,3H,6H,8H)-tetraones (bent pyrimidine-fused 5-deazaflavins) were synthesized by condensation of 7-alkylaminoquinazoline with 6-chloro-5-formyl-3-methyluracil. Also, their flavin analogs, 1,3,5,8,10,12-hexazanaphthacene-2,4,7,9(12H,3H,8H,10H)-tetraones (linear pyrimidine-fused flavins) and l,3,5,6,8,12-hexazabenz[a]anthracene-2,4,7,9(12H,3H,6H,8H)-tetraones (bent pyrimidine-fused flavins) were synthesized by cyclization of 7-[N-alkyl-N-(5-nitrouracil-6-yl)]aminoquin-azolines with the Vilsmeier reagent.     

Long range H,H coupling constants in cycloheptatrienes

The ¹H NMR spectra of 1,6-dicarbomethoxycyclohepta-1,3,5-triene ( 2 ) and 3,4-benzocyclohepta-1,3,5-triene ( 3 ) have been analysed in terms of chemical shifts and coupling constants. A method for the assignment of δ(AA′) and δ(BB′) in AA′BB′ systems, based on the observation of ¹³C satellites in the ¹H NMR spectrum, is described. For J(1,5) in 3 , a negative sign was established. Spin tickling experiments were used to determine the positive sign for J(2,5) in 2 and the negative sign for J(2,7) in 3. The conformation of 3 is discussed.     

Synthesis of 1,3,7,9,11,12,14-heptazapentacene-2,4,8,10-(14H,3H,9H,12H)-tetraones (mixed flavins) with oxidizing ability

1,3,7,9,11,12,14-Heptazapentacene-2,4,8,10(14H,3H,9 H,12H)-tetraones (mixed flavins) were synthesized by the cyclization of 1,5-dihydro-8-[N-alkyl-N-(5-nitrouracil-6-yl)]-amino-5- deazaflavins with the Vilsmeier reagent. The mixed flavins oxidized alcohol under neutral conditions in sunlight.     

Freezing-point of mixtures of H 2 16 O and H 2 18 O

Freezing-point depression of mixtures of H ₂ ¹⁶ O and H ₂ ¹⁸ O were measured. The results showed that the freezing point of the mixture rose linearly with an increase in the molal concentration of H ₂ ¹⁸ O. The results suggested the formation of a solid solution of H ₂ ¹⁶ O and H ₂ ¹⁸ O by freezing, similar to that formed by H ₂ O–D ₂ O, and that H ₂ ¹⁸ O behaves as a different molecule than H ₂ ¹⁶ O.     

Reduction of 4-arylidene-1,3-(2H,4H)isoquinolinediones

Catalytic hydrogenation of some 4-arylidene-1,3-(2H,4H)isoquinolinediones (1) afforded the corresponding 4-arylmethyl-1,3-(2H,4H)isoquinolinediones (2) , but reduction of 1 by sodium borohydride gave 4-arylmethyl-1(2H)isoquinolones (isocarbostyrils, 3). Compounds of type 1 studied had aryl substituents phenyl, 3,4-dimethoxyphenyl, 3,4-methyleneoxyphenyl and 2-furyl. In one example of sodium borohydride reduction of an N-methylisoquinolinedione derivative (1) the heterocylic ring was opened, and 2-(1-hydroxymethyl-2-phenylethenyl)-N-methylbenzamide (4) was obtained from 4-benzylidene-2-methyl-1,3-(2H,4H)isoquinolinedione.     

Temperature dependence of the rate constant of ionic analogs of H + H2 → H2 + H reaction by quantum instanton method

Rate constant ratios k(T)/k(1,500K) for two symmetrical reactions H^? + H₂ → H₂ + H^? and H⁺ + H₂ → H₂ + H⁺ are reported. Direct method based on quantum instanton approximation for evaluation of the temperature dependence of the quantum‐mechanical reaction rate constant is used. Implementation of the theory involves thermodynamic integration and path integral Monte Carlo method. Results of anionic case shows resemblance to neutral case, whereas cationic case is significantly different and below 1,000K rate constant shows strong deviation form linearity of Arrhenius plot due to high activation barrier. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Quinoxaline-2,3(1H,4H)-dithione: Synthesis and reactions

Quinoxaline-2,3(1H,4H)-dithione can be synthesized efficiently through the thionation of quinoxaline-2,3(1H,4H)-dione with phosphorous pentasulfide. It can also be obtained by reaction of 2,3-dichloroquinoxaline with thiourea or sodium hydrogen sulfide. The most common reactions of quinoxaline-2,3(1H,4H)-dithione involve deprotonation and electrophilic attack at the sulfur atoms to give various substituted derivatives and poly-fused heterocyclic ring systems. The current review aims to provide a survey of the developments in quinoxaline-2,3(1H,4H)-dithione chemistry until 2016.     

Condensation of 2,4(3H,5H)-furandione with heteroaromatic aldehydes

2,4(3H,5H)-Furaridione, 1 , condenses with heteroaromatic aldehydes in the presence of concentrated hydrochloric acid to yield 3-(heteroarylmethylene)-2,4(3H,5H)-furandiones, 4 . The condensation of 1 with acid sensitive aldehydes, including 2-furanacroleine and N-methylpyrrole-2-carboxaldehyde proceeded well with 1 as the sole proton source. The E/Z ratio of type 4 compounds was determined by ¹H-nmr spectroscopy.     

Arrhenius parameters for the reactions CH3. + C4H10 → CH4 + C4H9. and C2H5. + C4H10 → C2H6 + C4H9.

Study of n-butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions and of the Arrhenius parameters of the reactions Established data for k₁/k₂ allow estimation of k₁ for 951°K and this, with recent thermochemical data, yields the result log k_?1 (l.mole s^?1) = 8.5, in remarkable agreement with a recent measurement [20] but over si×ty times smaller than conventional assumption. The product k₃k₄ (l.²mole^?2s^?2) is found to be associated with the Arrhenius parameters log (A₃A₄) = 21.90 ± 0.6 and (E₃ + E₄) = 38.3 ± 2.7 kcal/mole. These values are much higher than would be e×pected on the basis of low temperature estimates. Independent evaluation gives log A₄ = 10.5 ± 0.4 (l.mole^?1s^?1) and E₄ = 20.1 ± 1.7 kcal/mole, hence log A₃ = 11.4 ± 0.8 (l.mole^?1s^?1) and E₃ = 18.2 ± 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical–alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.     

The rate constant for t-C4H9 → H + i-C4H8 and the thermodynamic parameters of t-C4H9

The rate of the reverse reaction of the system has been measured in the range of 584–604 K from a study of the azomethane sensitized pyrolysis of isobutane. Assuming the published value for the rate constant of recombination of t-butyl we obtain Combination with our published data for k₁ permits the evaluation We have modified a previously published structural model of t-butyl by the inclusion of a barrier to free rotation of the methyl groups in order to calculate values of the entropy and enthalpy of t-butyl as a function of temperature. Using standard data for H and for i-C₄H₈ we obtain We have obtained other, independent values of this quantity by a reworking of published data using our new calculations of the entropy and enthalpy of t-butyl. There is substantial agreement between the different values with one exception, namely, that derived from published data on the equilibrium which is significantly lower than the other values. We conclude that the value obtained from the present work and a reworking of published data which involves the use of experimental data on t-butyl recombination is incompatible with the result based on iodination data.     

A Shock Tube Study of H2 + OH → H2O + H Using OH Laser Absorption

The rate constant for the reaction of hydroxyl radicals (OH) with molecular hydrogen (H₂) was measured behind reflected shock waves using UV laser absorption of OH radicals near 306.69 nm. Test gas mixtures of H₂ and tert‐butyl hydroperoxide (TBHP) diluted in argon were shock‐heated to temperatures ranging from 902 to 1518 K at pressures of 1.15–1.52 atm. OH radicals were produced by rapid thermal decomposition of TBHP at high temperatures. The rate constant for the title reaction was inferred by best fitting the measured OH time histories with the simulated profiles from the comprehensive reaction mechanism of Wang et al. (USC‐Mech v2.0) (2007). The measured values can be expressed in the Arrhenius equation as k₁(T) = 4.38 × 10¹³ exp(–3518/T) cm³ mol^?1 s^?1 over the temperature range studied. A detailed error analysis was performed to estimate the overall uncertainty of the title reaction, and the estimated (2 – σ) uncertainties were found to be ±17% at 972 and 1228 K. The present measurements are in excellent agreement with the previous experimental studies from Frank and Just (Ber Bunsen‐Ges Phys Chem 1985, 89, 181–187), Michael and Sutherland (J Phys Chem 1988, 92, 3853–3857), Davidson et al. (Symp (Int) Combust 1988, 22, 1877–1885), Oldenborg et al. (J Phys Chem 1992, 96, 8426–8430), and Krasnoperov and Michael (J Phys Chem A 2004, 108, 5643–5648).In addition, the measured rate constant is in close accord with the non‐Arrhenius expression from GRI‐Mech 3.0 ( http://www.me.berkeley.edu/gri_mech/ ) and the theoretical calculation using semiclassical transition state theory from Nguyen et al. (Chem Phys Lett 2010, 499, 9–15).     

Electron-impact induced fragmentation of 3-hydroxy quinazoline-2,4(1H,3H) dione,pyridopyrimidine-2,4(1H,3H)diones,lumazine and alloxazine

Electron-bombardment of the N-3-hydroxy derivatives of the above-mentioned condensed uracils revealed that the major fragmentations involved the heterocyclic ring. The most intense ion proved to be the M-32 ion which was created by the loss of the NHOH radical from the molecular ion. Mechanisms for this transition are presented. Other fragmentations common to these systems are discussed and compared with those reported for the corresponding N-3 deoxy analogs of the title compounds. The mass spectral fragmentations of the O-methyl-, N-methyl- and O,N-dimethyl derivatives of 3-hydroxyquinazoline-2,4(1H,3H)dione were analyzed and were consistent with those expected from these structures. Electron bombardment of the 3-benzenesulfonyloxy derivatives of the title compounds resulted primarily in the scission of the sulfonate group in preference to that of the heterocyclic dione ring. These sulfonates also showed ions which indicated that a Lossen rearrangement had taken place in the mass spectrometer.     

Bruceines D,E and H

The absolute stereochemistry of bruceines D, E and H has been confirmed to be 1S, 5S, 7R, 8R, 9R, 10S, 11R, 12S, 13R, 14R, 15R and additionally 2S for bruceine E by a combination of 2D nmr [¹H-¹H and ¹H-¹³C (one-bond and long-range) COSY] nOe and cd spectroscopic analyses.     

Topological studies on IRC paths of X+H2→XH+H reactions

Topological properties of potential energy and electronic density distribution on five reaction paths X+H₂→XH+H (X=H, N, HN, H₂C, NC) are investigated at the level of UMP2/6–311G(d,p). It has been found that in the region of the reaction paths studied, where B(r_c)|_s>0 [B(r_c)|_s is the product of ρ(r_c) and ∇²ρ(r_c) at the point of reaction process, i.e., B(r_c)|_s=ρ(r_c)∇² ρ(r_c)] is basically the same as the region of V′(s)<0[V′(s) is the second derivative of potential energy with respect to the reaction coordinate, i.e., V′(s)=d²V/ds²], and the point with maximum B(r_c)|_s is almost coincident with the point of minimum V′(s). It can be concluded from the calculated results that there is a good correlation between the topological properties of potential energy and electronic density distribution along the reaction path. The structure transition state of such collinear reactions may be determined by topological analysis of electronic density. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1167–1174     

Quantum scattering LCAC-SW theory studies on reaction probabilities of three-dimensional H + H2 (v, j) → H2 (v′, j′) + H reaction

Upon the Liu, Siegbahn, Truhlar, Horowitz (LSTH) potential energy surface, the reaction probabilities of the three-dimensional (3-D) state-to-state H + H₂ (v, j) →H ₂(v′, j′) + H reaction are calculated with the linear combination of arrangement channels-scattering wavefunction (LCAC-SW) method. In the calculation, the vibration function of H₂ and the radial propagating wave functions are expanded by the real Gauss functions. The calculated threshold energy and the resonating structure are consistent with the results of the accurate quantum scattering calculations, which shows the accuration, simplicity and practicability of the LCAC-SW method. Project supported by the National Natural Science Fondation of China and the Doctoral Foundation of the State Education Commission of China.     

SCF MO LCGO studies on the hydration of ions: The systems H+H2O,Li+H2O,and Na+H2O

The energy surfaces of the systems LiOH ₂ ⁺ and NaOH ₂ ⁺ are studied for a number of different geometries within the SCF MO LCAO framework, using a gaussian basis set to approximate the wavefunction. In the minimum energy geometry of both systems the positive ion is bound to the oxygen atom of the water molecule. The computed binding energies and bond distances are: B ^SCF(LiOH ₂ ⁺ ) = 36.0 kcal/mole, d(LiO) = 3.57 a.u., and B ^SCF(NaOH ₂ ⁺ ) = 25.2 kcal/mole, d(NaO) = 4.23 a.u., resp. The results are compared with those of H₃O⁺ and discussed in view of ion-solvent interaction in aquous solutions.It is a pleasure to thank our technical staff for the careful preparation of the input for the programs and for its enthusiastic and skilful assistance in running the computer.     

Monohalogenated ferrocenes C5H5FeC5H4X (X = Cl,Br and I) and a second polymorph of C5H5FeC5H4I

The structures of the three title monosubstituted ferrocenes, namely 1‐chloroferrocene, [Fe(C₅H₅)(C₅H₄Cl)], (I), 1‐bromoferrocene, [Fe(C₅H₅)(C₅H₄Br)], (II), and 1‐iodoferrocene, [Fe(C₅H₅)(C₅H₄I)], (III), were determined at 100 K. The chloro‐ and bromoferrocenes are isomorphous crystals. The new triclinic polymorph [space group P, Z = 4, T = 100 K, V = 943.8 (4) ų] of iodoferrocene, (III), and the previously reported monoclinic polymorph of (III) [Laus, Wurst & Schottenberger (2005). Z. Kristallogr. New Cryst. Struct. 220 , 229–230; space group Pc, Z = 4, T = 100 K, V = 924.9 ų] were obtained by crystallization from ethanolic solutions at 253 and 303 K, respectively. All four phases contain two independent molecules in the unit cell. The relative orientations of the cyclopentadienyl (Cp) rings are eclipsed and staggered in the independent molecules of (I) and (II), while (III) demonstrates only an eclipsed conformation. The triclinic and monoclinic polymorphs of (III) contain nonbonded intermolecular I...I contacts, causing different packing modes. In the triclinic form of (III), the molecules are arranged in zigzag tetramers, while in the monoclinic form the molecules are arranged in zigzag chains along the a axis. Crystallographic data for (III), along with the computed lattice energies of the two polymorphs, suggest that the monoclinic form is more stable.     

6(5H)-phenanthridinones. III. halo-6(5H)phenanthridinones

Halogenation of 6(5H)-phenanthridinone or its 3,8-dihalo derivatives with N-bromo or N-chlorosuccinimide in dimethylformamide gives the corresponding 2-halophenanthridinones (I,V,XI-XIV). Further halogenation of 2-halo-6(5H)-phenanthridinone with the appropriate N-halosuccinimide, in the same medium, gives the corresponding 2,4-dihalo derivatives (II,VI). NXS/DMF is found to be a very convenient halogenating system in these preparations. 1,3,8-Trihalo-6(5H)-phenanthridinones (XIX,XX) are prepared from the 1-nitro derivatives which are obtained by a Schmidt rearrangement of 2,7-dihalo-4-nitro-9-oxofluorenes. Similarly, rearrangement and further reaction of 2-nitro-5-chloro-9-oxofluorene (XXI) leads to 3,10-dichloro-6(5H)-phenanthridinone (XXIV). UV absorptions as well as selected IR absorptions of these 6(5H)-phenanthridinones are described.