Molecular Elimination Research Articles

Roaming mediated nonadiabatic dynamics in molecular hydrogen elimination from propane at 157 nm

The photofragmentation dynamics study using Tully’s fewest switches trajectory surface hopping calculations, based on MRCIS(6,6)/6-31++G∗∗ potential energy surfaces, energy gradients and nonadiabatic couplings, reveals the occurrence of roaming mediated nonadiabatic pathways for the elimination of molecular hydrogen from propane at 157nm. 1,2- and 1,3-molecular hydrogen eliminations, the minor dissociation channels, exclusively follow roaming (of partially dissociated H atom) mediated nonadiabatic pathway (S1→S0) to the ground electronic state followed by an atomic hydrogen abstraction from another carbon atom in the ground singlet (S0) state. 1,1- and 2,2-molecular hydrogen eliminations on the other hand, the major dissociation processes, proceed either adiabatically in the first excited singlet (S1) electronic state or through the internal conversion S1→S0 followed by direct two-body fragmentation in the ground singlet (S0) state, with equal probability.

Auger decay and subsequent fragmentation pathways of ethylene followingK-shell ionization

The fragmentation pathways and dynamics of ethylene molecules after core ionization are explored using coincident measurements of the Auger electron and fragment ions by employing the cold target recoil-ion momentum spectroscopy method. The influence of several factors on the dynamics and kinematics of the dissociation is studied. These include propensity rules, ionization mechanisms, symmetry of the orbitals from which the Auger electrons originate, multiple scattering, conical intersections, interference, and possible core-hole localization for the double ionization of this polyatomic molecule. Energy correlation maps allow probing the multidimensional potential energy surfaces and, in combination with our multiconfiguration self-consistent field calculations, identifying the populated electronic states of the dissociating dication. The measured angular distributions of the Auger electrons in the molecular frame further support and augment these assignments. The deprotonation and molecular hydrogen ion elimination channels show a nearly isotropic Auger electron angular distribution with a small elongation along the direction perpendicular to the molecular axis. For the symmetric breakup the angular distributions show a clear influence of multiple scattering on the outgoing electrons. The lowest kinetic energy release feature of the symmetric breakup channel displays a fingerprint of entangled Auger and photoelectron motion in the angular emission pattern identifying this transition as an excellent candidate to probe core-hole localization at a conical intersection of a polyatomic molecule.

Experimental and kinetic modeling study of the shock tube ignition of a large oxygenated fuel: Tri-propylene glycol mono-methyl ether

Tri-propylene glycol monomethyl ether (TPGME) is an important oxygenated fuel additive that can be used to reduce soot in diesel engines. However, a validated chemical kinetic model that incorporates the low- to high-temperature chemistry, needed to simulate ignition in a diesel engine is not available for TPGME. In addition, no fundamental experimental data are available that can be used to validate a TPGME mechanism. In this study, a surrogate chemical kinetic model for TPGME that includes low- and high-temperature chemistry has been developed, and shock tube ignition delay time data has been acquired for its validation at 0.25% TPGME for temperatures in the range of 980–1545K, at pressures of 10 and 20atm, and at equivalence ratios of φ=0.5, 1.0 and 2.0. The predictions from the model have been compared to the experimental measurements with good agreement. Under the experimental conditions investigated in the shock tube, TPGME was found to be consumed by molecular elimination reactions and also H-atom abstraction by Ḣ atoms and by ȮH and HȮ2 radicals. In performing sensitivity analyses it was found that the ignition of TPGME is most sensitive to reactions involving propene. Considering how the sensitivity analyses change with pressure, the most sensitive reactions involved Ḣ atoms at 10atm and HȮ2 radicals at 20atm. With respect to the effect of equivalence ratio, reactions involving Ḣ atoms are relatively more sensitive under fuel-rich conditions while those involving HȮ2 radicals are relatively more sensitive under fuel-lean conditions. Further experimental work is needed to enable validation of the model under low-temperature conditions. TPGME was compared to n-heptane which has similar ignition properties based on Cetane Number. Predictions showed that TPGME has a higher overall reactivity compared to n-heptane. In addition, TPGME is shown to produce significantly less soot precursor species when TPGME predictions are compared to n-heptane.

Theoretical study of molecular hydrogen elimination from the undecahydrodecaborate monoanion [B10H11]−. Exopolyhedral substitution intermediates: [B10H9]− monoanion and neutral [B10H10] cluster

The elementary reaction of molecular hydrogen elimination from the [B10H11]− anion, which is presumably the rate-limiting stage of acid-catalyzed reactions of substitution of exopolyhedral H atoms in the [B10H10]2− decahydro-closo-decaborate anion, has been calculated by the density functional theory method (in the B3LYP/6-311++G** approximation). Specific transition states of H2 elimination in which vacancies form near the boron atoms have been localized. It has been demonstrated that regioselectivity of substitution reactions can be related to the significant difference between the activation barriers for the pathways of H2 elimination from boron atoms with different coordination numbers (CN 6 and 5). The electron density of the [B10H9]− anion that forms after hydrogen molecule elimination has a characteristic shape of the lowest unoccupied molecular orbital for the interaction with nucleophilic reagents; in acid-catalyzed reactions, different anions, for example, a carboxylic acid residue, can act as such. The direct reaction of the [B10H9]− intermediate with nucleophilic anions is hindered by the Coulomb charge repulsion. To overcome this hindrance, the possibility of [B10H9]− protonation to form the neutral [B10H10] system has been considered. It has been shown that the proton affinity of the [B10H9]− anion is ∼280–290 kcal/mol. For the [B10H10] cluster, the lowest-lying and low-lying isomers have been considered. For all the systems under consideration, the electronic chemical potential and Pearson hardness have been evaluated.

Thermochemistry, reaction paths, and kinetics on the tert-isooctane radical reaction with O2.

Thermochemical properties of tert-isooctane hydroperoxide and its radicals are determined by computational chemistry. Enthalpies are determined using isodesmic reactions with B3LYP density function and CBS QB3 methods. Application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations for the lowest energy conformer. Internal rotor potentials are determined for the tert-isooctane hydroperoxide and its radicals in order to identify isomer energies. Recommended values derived from the most stable conformers of tert-isooctane hydroperoxide of are -77.85 ± 0.44 kcal mol(-1). Isooctane is a highly branched molecule, and its structure has a significant effect on its thermochemistry and reaction barriers. Intramolecular interactions are shown to have a significant effect on the enthalpy of the isooctane parent and its radicals on peroxy/peroxide systems, the R• + O2 well depths and unimolecular reaction barriers. Bond dissociation energies and well depths, for tert-isooctane hydroperoxide → R• + O2 are 33.5 kcal mol(-1) compared to values of ∼38 to 40 kcal mol(-1) for the smaller tert-butyl-O2 → R• + O2. Transition states and kinetic parameters for intramolecular hydrogen atom transfer and molecular elimination channels are characterized to evaluate reaction paths and kinetics. Kinetic parameters are determined versus pressure and temperature for the chemically activated formation and unimolecular dissociation of the peroxide adducts. Multifrequency quantum RRK (QRRK) analysis is used for k(E) with master equation analysis for falloff. The major reaction paths at 1000 K are formation of isooctane plus HO2 followed by cyclic ether plus OH. Stabilization of the tert-isooctane hydroperoxy radical becomes important at lower temperatures.

Photodissociation dynamics of allyl chloride at 200 and 266 nm studied by time-resolved mass spectrometry and photoelectron imaging.

The photodissociation dynamics of allyl chloride at 200 and 266 nm has been studied by femtosecond time-resolved mass spectrometry coupled with photoelectron imaging. The molecule was prepared to different excited states by selectively pumping with 400 or 266 nm pulse. The dissociated products were then probed by multiphoton ionization with 800 nm pulse. After absorbing two photons at 400 nm, several dissociation channels were directly observed from the mass spectrum. The two important channels, C-Cl fission and HCl elimination, were found to decay with multiexponential functions. For C-Cl fission, two time constants, 48 ± 1 fs and 85 ± 40 ps, were observed. The first one was due to the fast predissociation process on the repulsive nσ*/πσ* state. The second one could be ascribed to dissociation on the vibrationally excited ground state which is generated after internal conversion from the initially prepared ππ* state. HCl elimination, which is a typical example of a molecular elimination reaction, was found to proceed with two time constants, 600 ± 135 fs and 14 ± 2 ps. We assigned the first one to dissociation on the excited state and the second one to the internal conversion from the ππ* state to the ground state and then dissociation on the ground state. As we excited the molecule with 266 nm light, the transient signals decayed exponentially with a time constant of ∼48 fs, which is coincident with the time scale of C-halogen direct dissociation. Photoelectron images, which provided translational and angular distributions of the generated electron, were also recorded. Detailed analysis of the kinetic energy distribution strongly suggested that C3H4(+) and C3H5(+) were generated from ionization of the neutral radical. The present study reveals the dissociation dynamics of allyl chloride in a time-resolved way.

Theoretical Study on Dissociation Mechanisms of Di-ethyl Berylliums and Di-t-butyl Berylliums

The potential energy surfaces (PES) of unimolecular dissociation reactions for di-ethyl beryllium and di-t-butyl beryllium are investigated by B3LYP, CCSD(T), and G3B3 approaches. Possible reaction pathways through either the radical or transition state (TS) of the molecules are considered. The geometries, vibrational frequencies and relative energies for various stationary points are determined. From the study of energetics, the TS pathways arising from concerted molecular eliminations are indicated to be the main dissociation pathways for both molecules. The PES differences of the dissociation reactions are investigated. The activation energies and rate constants will be helpful for investigating the predictive ability of the reaction in further theoretical and experimental research.

Photodissociation of water and O(3PJ) formation on a lunar impact melt breccia

AbstractPhotodissociation of water deposited on an impact melt breccia collected during Apollo 16 was studied by measuring O(3PJ = 2,1,0) photoproducts detected with resonance‐enhanced multiphoton ionization. For each spin‐orbit state, the oxygen atom time‐of‐flight (TOF) spectrum was measured as a function of H2O exposure and 157 nm irradiation time. Four Maxwell‐Boltzmann distributions with translational temperatures of 10,000 K, 1800 K, 400 K, and 102 K were required to fit the data. The most likely formation mechanisms are molecular hydrogen elimination following ion‐electron recombination, secondary recombination of hydroxyl radicals, and photodissociation of adsorbed hydroxyls. The irradiation time required to reach maximum oxygen signal suggests that water clusters into islands when adsorbing on the lunar impact melt breccia. After enough irradiation for the oxygen atom yield to reach its maximum, the slowly decreasing signal was fit with an exponential curve to obtain a cross section that represents the rate of surface hydroxyl depletion. For 0.1, 1, and 5 Langmuir (1 L = 10−6 Torr s) H2O exposure, respectively, the measured O(3P) depletion cross sections were 4.9 × 10−20, 6.6 × 10−20, and 4.6 × 10−20 cm2. These results imply that photodissociation of water on the lunar surface cannot account for the large mass‐16 (±1 amu) signal observed in the lunar atmosphere. Unless another significant source of oxygen atoms is present, this unexpectedly large signal is likely due to CH4 or OH.

O(3PJ) formation and desorption by 157-nm photoirradiation of amorphous solid water

Photodissociation of amorphous solid water (ASW) deposited on a thinly oxidized copper substrate at 82 K was studied by measuring O((3)PJ=2,1,0) photoproducts detected with resonance-enhanced multiphoton ionization. For each spin-orbit state, the oxygen atom time-of-flight spectrum was measured as a function of H2O exposure, which is related to ice thickness, and 157-nm irradiation time. Four Maxwell-Boltzmann distributions with translational temperatures of 10,000 K, 1800 K, 400 K, and 82 K were found to fit the data. The most likely formation mechanisms are molecular elimination following ionization of water and ion-electron recombination, secondary recombination of hydroxyl radicals, and photodissociation of adsorbed hydroxyl radicals. Evidence for O-atom diffusion through bulk ASW was found for H2O exposures of at least 5 Langmuir (1 L = 10(-6) Torr s). The cross sections for O((3)P2) depletion were 1.3 × 10(-19) and 6.5 × 10(-20) cm(2) for 1 and 5 L, respectively.

Molecular halogen elimination from halogen-containing compounds in the atmosphere

Atmospheric halogen chemistry has drawn much attention, because the halogen atom (X) playing a catalytic role may cause severe stratospheric ozone depletion. Atomic X elimination from X-containing hydrocarbons is recognized as the major primary dissociation process upon UV-light irradiation, whereas direct elimination of the X2 product has been seldom discussed or remained a controversial issue. This account is intended to review the detection of X2 primary products using cavity ring-down absorption spectroscopy in the photolysis at 248 nm of a variety of X-containing compounds, focusing on bromomethanes (CH2Br2, CF2Br2, CHBr2Cl, and CHBr3), dibromoethanes (1,1-C2H4Br2 and 1,2-C2H4Br2) and dibromoethylenes (1,1-C2H2Br2 and 1,2-C2H2Br2), diiodomethane (CH2I2), thionyl chloride (SOCl2), and sulfuryl chloride (SO2Cl2), along with a brief discussion on acyl bromides (BrCOCOBr and CH2BrCOBr). The optical spectra, quantum yields, and vibrational population distributions of the X2 fragments have been characterized, especially for Br2 and I2. With the aid of ab initio calculations of potential energies and rate constants, the detailed photodissociation mechanisms may be comprehended. Such studies are fundamentally important to gain insight into the dissociation dynamics and may also practically help to assess the halogen-related environmental variation.

Thermal decomposition products of butyraldehyde

The thermal decomposition of gas-phase butyraldehyde, CH3CH2CH2CHO, was studied in the 1300-1600 K range with a hyperthermal nozzle. Products were identified via matrix-isolation Fourier transform infrared spectroscopy and photoionization mass spectrometry in separate experiments. There are at least six major initial reactions contributing to the decomposition of butyraldehyde: a radical decomposition channel leading to propyl radical + CO + H; molecular elimination to form H2 + ethylketene; a keto-enol tautomerism followed by elimination of H2O producing 1-butyne; an intramolecular hydrogen shift and elimination producing vinyl alcohol and ethylene, a β-C-C bond scission yielding ethyl and vinoxy radicals; and a γ-C-C bond scission yielding methyl and CH2CH2CHO radicals. The first three reactions are analogous to those observed in the thermal decomposition of acetaldehyde, but the latter three reactions are made possible by the longer alkyl chain structure of butyraldehyde. The products identified following thermal decomposition of butyraldehyde are CO, HCO, CH3CH2CH2, CH3CH2CH=C=O, H2O, CH3CH2C≡CH, CH2CH2, CH2=CHOH, CH2CHO, CH3, HC≡CH, CH2CCH, CH3C≡CH, CH3CH=CH2, H2C=C=O, CH3CH2CH3, CH2=CHCHO, C4H2, C4H4, and C4H8. The first ten products listed are direct products of the six reactions listed above. The remaining products can be attributed to further decomposition reactions or bimolecular reactions in the nozzle.

Novel Approaches of Genomic DNA Isolation for Identification of Cultivable Bacteria

Background: Identification of novel pathogenic bacteria always has a crucial role in clinical microbiology to defeat uncontrolled diseases. Objectives: Sample preparation platform has been developed for rapid and simple detection of infectious organisms from the point of care diagnostics and molecular manipulation by using three novel genomic DNA isolation protocols. Materials and Methods: Most of the genomic DNA isolation protocols are represented with SDS, alkaline lysis with extraction buffer and phenol, organic chloroform extractions and then enzymatic purifications, but in our reconnoiter, we only used three single chemicals including ethanol, phenol and hydrogen peroxide which are major disinfectants and sterilizers, acting on the cell wall and cell membrane proteins, followed by denaturation of the bacterial cell and simultaneous lysis. Results: This study used the mentioned three major chemicals in three different protocols to avoid unnecessary purification steps especially for gene amplification and diagnostics reports. Genomic DNA was recovered by adding 50µL double distilled water. Conceivably, we applied this principle for three novel DNA extraction methods and succeeded to achieve purified high-yield DNA. Conclusions: Purified high-yield DNA was obtained for molecular manipulations and elimination of diagnostic concerns.

Effect of trimethylsilane pressure on hot-wire chemical vapor deposition chemistry using vacuum ultraviolet laser ionization mass spectrometry

In this study, the authors investigated the effect of sample pressure on the reaction chemistry of trimethylsilane (TriMS) in the hot-wire chemical vapor deposition (CVD) process. The secondary gas-phase reaction products were examined in a reactor with varying TriMS pressures. The reaction products were analyzed using a laser ionization source with a vacuum ultraviolet wavelength of 118 nm, coupled with mass spectrometry. By increasing TriMS pressure, methane formation was observed. To our knowledge, this is the first successful use of either open-chain alkylsilanes or four-membered-ring (di)silacyclobutane molecules as an independent precursor gas in the hot-wire CVD reactor to achieve methane formation. Our results showed that methane was formed mainly from the radical chain reactions with minor contributions from molecular elimination. The increase in the sample pressure also led to the formation of other small hydrocarbon molecules including acetylene, ethene, propyne, and propene. The formation of hydrogen molecules was enhanced when the sample pressure was increased. In addition, the change in the sample pressure had a direct effect on the radical recombination and disproportionation reactions. This is reflected in the different behavior assumed by the main products from these two types of reactions, i.e., tetramethylsilane, hexamethyldisilane from the former, and three methyl-substituted disilacyclobutanes from the latter. The trapping of free radicals resulting from the in-situ produced ethene and propene molecules is responsible for the observed difference.

The Roles of Dihydrogen Bonds in Amine Borane Chemistry

A dihydrogen bond (DHB) is an electrostatic interaction between a protonic hydrogen and a hydridic hydrogen. Over the past two decades, researchers have made significant progress in the identification and characterization of DHBs and their properties. In comparison with conventional hydrogen bonds (HBs), which have been widely used in catalysis, molecular recognition, crystal engineering, and supramolecular synthesis, chemists have only applied DHBs in very limited ways. Considering that DHBs and conventional HBs have comparable strength, DHBs could be more widely applied in chemistry. Over the past several years, we have explored the impact of DHBs on amine borane chemistry and the syntheses and characterization of amine boranes and ammoniated metal borohydrides for hydrogen storage. Through systematic computational and experimental investigations, we found that DHBs play a dominant role in dictating the reaction pathways (and thus different products) of amine boranes where oppositely charged hydrogens coexist for DHB formation. Through careful experiments, we observed, for the first time, a long-postulated reaction intermediate, ammonia diborane (AaDB), whose behavior is essential to mechanistic understanding of the formation of the diammoniate of diborane (DADB) in the reaction of ammonia (NH3) with tetrahydrofuran borane (THF·BH3). The formation of DADB has puzzled the boron chemistry community for decades. Mechanistic insight enabled us to develop facile syntheses of aminodiborane (ADB), ammonia borane (AB), DADB, and an inorganic butane analog NH3BH2NH2BH3 (DDAB). Our examples, together with those in the literature, reinforce the fact that DHB formation and subsequent molecular hydrogen elimination are a viable approach for creating new covalent bonds and synthesizing new materials. We also review the strong effects of DHBs on the stability of conformers and the hydrogen desorption temperatures of boron-nitrogen compounds. We hope that this Account will encourage further applications of DHBs in molecular recognition, host-guest chemistry, crystal engineering, supramolecular chemistry, molecular self-assembly, chemical kinetics, and the syntheses of new advanced materials.

Molecular elimination of Br2 in photodissociation of CH2BrC(O)Br at 248 nm using cavity ring-down absorption spectroscopy

The primary elimination channel of bromine molecule in one-photon dissociation of CH(2)BrC(O)Br at 248 nm is investigated using cavity ring-down absorption spectroscopy. By means of spectral simulation, the ratio of nascent vibrational population in v = 0, 1, and 2 levels is evaluated to be 1:(0.5 ± 0.1):(0.2 ± 0.1), corresponding to a Boltzmann vibrational temperature of 581 ± 45 K. The quantum yield of the ground state Br(2) elimination reaction is determined to be 0.24 ± 0.08. With the aid of ab initio potential energy calculations, the obtained Br(2) fragments are anticipated to dissociate on the electronic ground state, yielding vibrationally hot Br(2) products. The temperature-dependence measurements support the proposed pathway via internal conversion. For comparison, the Br(2) yields are obtained analogously from CH(3)CHBrC(O)Br and (CH(3))(2)CBrC(O)Br to be 0.03 and 0.06, respectively. The trend of Br(2) yields among the three compounds is consistent with the branching ratio evaluation by Rice-Ramsperger-Kassel-Marcus method. However, the latter result for each molecule is smaller by an order of magnitude than the yield findings. A non-statistical pathway so-called roaming process might be an alternative to the Br(2) production, and its contribution might account for the underestimate of the branching ratio calculations.

DFT and ab-initio study on the mechanism of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their isomerization

The mechanisms of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their interconversion have been examined at MP2 and DFT levels of theory. These halide substrates yield isoprene and hydrogen chloride. The results MPW1PW91 calculations agree with the experimental kinetic parameters showing the elimination reaction occurs at greater rate for 1-chloro-3-methylbut-2-ene than that for the 3-chloro-3-methylbut-1-ene isomer. The mechanism for the molecular elimination of 1-chloro-3-methylbut-2-ene suggests proceeding through an uncommon six-membered cyclic transition state for alkyl halides in the gas phase, while 3-chloro-3-methylbut-1-ene eliminates through the usual four-membered cyclic transition state. The elongation and subsequent polarization of the C-Cl bond, in the direction of C^{δ+}…Cl^{δ-}, is rate determining step of these reactions. The isomerization of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene was additionally studied. The 1-chloro-3-methylbut-2-ene converts to 3-chloro-3-methylbut-1-ene easier than the reverse reaction. This means that 1-chloro-3-methylbut-2-ene was found thermodynamically more stable than 3-chloro-3-methylbut-1-ene.

Interaction of vanadium oxide cluster anions with water: an experimental and theoretical study on reactivity and mechanism

Vanadium oxide cluster anions (V(x)O(y)(-), x = 2-3; y = 3-7) are produced by laser ablation and reacted with water in a fast flow reactor. A time-of-flight mass spectrometer is used to detect the cluster distribution before and after the reactions. Reaction channels of molecular hydrogen elimination (for V(2,3)O(3)(-)), water association (for V(2)O(5)(-) and V(3)O(6,7)(-)) and the coexistence of both channels (for V(2)O(4)(-) and V(3)O(4,5)(-)) are observed. V(2)O(6)(-) and V(3)O(8)(-) are nearly inert toward water. Density functional theory (DFT) calculations are performed to study the reaction mechanism of V(2)O(3)(-) in different spin states with water and the results support the experimental observation. The reaction mechanism of V(2)O(3)(+) with water is also studied, which is in agreement with the experimental report in previous literature [Eur. J. Inorg. Chem., 2008, 4961] that molecular hydrogen elimination is a minor reaction channel for V(2)O(3)(+) + H(2)O. The influence of cluster charge states and oxidation states of vanadium atoms on the cluster reactivity are presented based on the experimental and theoretical studies.

After-effects of lithium-mediated alumination of 3-iodoanisole: isolation of molecular salt elimination and trapped-benzyne products

Gaining a deeper understanding of the modus operandi of heterometallic lithium aluminate bases towards deprotonative metallation of substituted aromatic substrates, we have studied the reactions and their aftermath between our recently developed bis-amido base '(i)Bu(2)Al(μ-TMP)(2)Li'3 and 3-halogenated anisoles. Ortho-metallation of 3-iodoanisole with 3 results in a delicately poised heterometallic intermediate whose breakdown into homometallic species and benzyne cannot be suppressed, even at low temperature or in a non-polar solvent (hexane). Homometallic components [LiI·TMP(H)](4) (5) and (i)Bu(2)Al(TMP)·THF (6) have been isolated while the reactive benzyne intermediate has been trapped via Diels-Alder cyclization with 1,3-diphenylisobenzofuran yielding 1-methoxy-9-10-diphenyl-9-10-epoxyanthracene (7). In polar THF solution, nucleophilic addition of LiTMP across the benzyne functionality followed by electrophilic quenching with iodine yields the trisubstituted aromatic species 1-(2-iodo-3-methoxyphenyl)-2,2,6,6-tetramethylpiperidide (8). Compounds 5-8 have been characterized by single-crystal X-ray diffraction in the solid state and multinuclear NMR spectroscopy in solution. By considering these collated results, a plausible reaction mechanism has been proposed for the breakdown of the aforementioned intermediate bimetallic framework. Interestingly, the metallation reaction can be controlled by changing to 3-chloroanisole with an excess of base 3, as evidenced by electrophilically trapping the deprotonated aromatic with iodine to give 2-iodo-3-chloroanisole (9).

Br2 molecular elimination in photolysis of (COBr)2 at 248 nm by using cavity ring-down absorption spectroscopy: A photodissociation channel being ignored

A primary dissociation channel of Br(2) elimination is detected following a single-photon absorption of (COBr)(2) at 248 nm by using cavity ring-down absorption spectroscopy. The technique contains two laser beams propagating in a perpendicular configuration. The tunable laser beam along the axis of the ring-down cell probes the Br(2) fragment in the B(3)Π(ou)(+)-X(1)Σ(g)(+) transition. The measurements of laser energy- and pressure-dependence and addition of a Br scavenger are further carried out to rule out the probability of Br(2) contribution from a secondary reaction. By means of spectral simulation, the ratio of nascent vibrational population for v = 0, 1, and 2 levels is evaluated to be 1:(0.65 ± 0.09):(0.34 ± 0.07), corresponding to a Boltzmann vibrational temperature of 893 ± 31 K. The quantum yield of the ground state Br(2) elimination reaction is determined to be 0.11 ± 0.06. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state (COBr)(2) via internal conversion. A four-center dissociation mechanism is followed synchronously or sequentially yielding three fragments of Br(2) + 2CO. The resulting Br(2) is anticipated to be vibrationally hot. The measurement of a positive temperature effect supports the proposed mechanism.

The graphite oxide photoreduction mechanism

The mechanisms of dissociation of oxygen-containing moieties (-OH, -HCO, -COOH) upon the photoreduction of graphite oxide by UV light have been considered. It has been concluded that the photoreduction, which involves the detachment of the OH group and the molecular elimination of CO and CO2, occurs in singlet excited states. The energy threshold of the photoreduction processes is determined by the position of the repulsive terms of the system.