2053-29-4

The thermal decomposition of CH3NH2 was studied by IR laser kinetic absorption spectroscopy behind reflected shock waves with 1400 5 5 -3.The absorption profiles were satisfactorily modeled with a 28-reaction mechanism based on earlier investigations.The initial decomposition was found to be dominated by CH3NH2 + M -> CH3 + NH2 + M (ΔHo0 = 350 kJ) under these conditions, for which the rate constant expression ka = 5E17 exp(-260kJ/RT) cm3 mol-1 s-1 was derived.

Very low pressure vapor phase pyrolysis (flash thermolysis) of four-membered ring compounds was followed by microwave spectroscopic detection of the reaction products.The molecules studied included substituted cyclobutanes, thietanes, oxetane and azetidine.Microwave spectroscopy is well suited not only to observe stable reaction products but also to detect unstable species formed during pyrolysis.The investigation provided a wealth of information on typical decomposition patterns during pyrolysis of four-membered ring compounds.In addition, new methods were found for producing some unstable molecules with improved efficiency.

IR spectra of azidomethane, 3-azidopropyne and 3-azido-1-d-propyne in nitrogen matrices have been recorded during UV photolysis.In contrast to the simple photolytic reaction of matrix isolated azidomethane (azidomethane -> methyleneimine -> HCN + HNC), 3-azidopropyne apparently displays more complex reaction paths.

The competitive adsorption of catalyst poisons and adsorbed H is of interest in relation to their effects in promoting H absorption into transition metals. The capacity of three sulfur-containing compounds, thiourea, L-cysteine and 2,2′-diethanolsulfide (DES), to block H adsorption at Pt electrodes in both the underpotential deposition (UPD) and overpotential deposition (OPD) regions is studied. Differences in the rates of adsorption (cysteine and DES cysteine and DES) are shown to play important roles in the extent to which the poison, P, can block the UPD of H and modify the Tafel relationship for the hydrogen evolution reaction (HER). The relative H blocking, due to poison coverage, θP, is measured by means of cyclic voltammetry and potential-relaxation transient experiments. Measurements of rates of the HER as a function of overpotential are also made utilizing steady-state techniques. It is shown that, for θP of cysteine and DES 2 evolution takes place, θP varies with potential according to an isotherm determined by the kinetics of hydrogenation and/or desorption of the poison.

Although N-heterocyclic carbenes have been well-studied, the simplest aminocarbene, aminomethylene H?C??NH2, has not been spectroscopically identified to date. Herein we report the gas-phase preparation of aminomethylene by high-vacuum flash py

The influence of the position of the methyl substituent in 1- and 2-methyl-substituted 5-aminotetrazoles on the photochemistry of these molecules is evaluated. The two compounds were isolated in an argon matrix (15 K) and the matrix was subjected to in situ narrowband UV excitation at different wavelengths, which induce selectively photochemical transformations of different species (reactants and initially formed photoproducts). The progress of the reactions was followed by infrared spectroscopy, supported by quantum chemical calculations. It is shown that the photochemistries of the two isomers, 1-methyl-(1H)-tetrazole-5-amine (1a) and 2-methyl-(2H)-tetrazole-5-amine (1b), although resulting in a common intermediate diazirine 3, which undergoes subsequent photoconversion into 1-amino-3-methylcarbodiimide (H2N-N=C=N-CH3), show marked differences: formation of the amino cyanamide 4 (H2N-N(CH3)-C=N) is only observed from the photocleavage of the isomer 1a, whereas formation of the nitrile imine 2 (H2N-C-=N+=N-CH3) is only obtained from photolysis of 1b. The exclusive formation of nitrile imine from the isomer 1b points to the possibility that only the 2H-tetrazoles forms can give a direct access to nitrile imines, while observation of the amino cyanamide 4 represents a novel reaction pathway in the photochemistry of tetrazoles and seems to be characteristic of 1H-tetrazoles. The structural and vibrational characterization of both reactants and photoproducts has been undertaken.

This paper presents the first experimental investigation under collisionless conditions of the competing photodisssociation channels of methylamine excited in the first ultraviolet absorption band.Measurement of the nascent photofragments' velocity distributions and preliminary measurements of some photofragments' angular distributions evidence four significant dissociation channels at 222 nm: N-H, C-N, and C-H bond fission and H2 elimination.The data, taken on photofragments from both methylamine and methylamine-d2, elucidate the mechanism for each competing reaction.Measurement of the emission spectrum of methylamine excited at 222 nm gives complementary information, evidencing a progression in the amino wag (or inversion) and combination bands with one quantum in the methyl(umbrella) deformation or with two quanta in the amino torsion vibration.The emission spectrum reflects the forces in the Franck-Condon region which move the molecule toward a ciscoid geometry.The photofragment kinetic energy distributions measured for CH3ND2 show that hydrogen elimination occurs via a four-center transition state to produce HD and partitions considerable energy to relative product translation.The reaction coordinates for N-H and C-N fission are analyzed in comparison to that for ammonia dissociation from the state and with reference to ab iniitio calculations of cuts along the excited state potential energy surface of methylamine which show these reactions traverse a small barrier in the excited state from a Rydberg/valence avoided crossing and then encounter a conical intersection in the exit channel.The measured kinetic energy distribution of the C-N bond fission photofragments indicates that the NH2 (ND2) product is formed in the 2A1 state; the C-N fission reactive trajectories thus remain on the upper adiabat as they traverse the conical intersection.The mechanism for C-H bond fission is less clear; most of the kinetic energy distribution indicates the reaction evolves on a potential energy surface with no barrier to the reverse reaction, consistent with dissociation along the excited state surface or upon internal conversion to the ground state, but some of the distribution reflects more substantial partitioning to relative translation, indicating that some molecules may dissociate via a repulsive triplet surface.In general, the photofragment angular distributions were anisotropic, but the measured β ca. -0.4 +/- 0.4 for C-N bond fission indicates dissociation is not instantaneous on the time scale of molecular rotation.We end with analyzing why in methylamine three other primary dissociation channels effectively compete with N-H fission while in CH3OH and CH3SH primarily O-H and S-H fission, respectively, dominate.

Methoxyisocyanate (1) can be prepared by photolysis of methyl azidoformate (3) or pyrolysis of N-methoxycarbonyl-O-methylhydroxylamine (4).Aminoisocyanate (2) is similarly formed on photolysis of carbamoyl azide (12) and pyrolysis of either methyl carbazate (13) or 3,4-diaminofurazan (14).The infrared spectra of 1 and 2 in an argon matrix at 10 K have been measured, and some of their properties are discussed. - Keywords: Flash pyrolysis/ Matrix IR spectroscopy/ Photolysis

We report here on the gas-phase chemistry of a number of bare transition metal-nitrene and -imido ion complexes, MNH+.Group 3, 4, and 5 atomic metal ions react with NH3 at thermal energies to generate MNH+ via dehydrogenation.A reaction mechanism is proposed involving initial oxidative addition to an N-H bond, in analogy to mechanisms proposed for reactions of gaseous atomic metal ions with hydrocarbons.Cr+ reacts with NH3 via slow condensation to form CrNH3+, as do all group 6-11 atomic metal ions investigated.However, excited-state Cr+ reacts with NH3 via bond-insertion reactions to form CrNH2+ and CrNH+.An unidentified metastable electronic state of Cr+, produced by direct laser desorption of chromium foil, reats with much higher efficiency than does kinetically excited Cr+.FeO+ reacts with NH3 to generate FeNH+ with loss of H2O.Thermochemical studies of VNH+ and FeNH+ involving ion-molecule reactions indicate values of D0(V+-NH) = 101 +/- 7 kcal/mol and D0(Fe+-NH) = 54 +/- 14 kcal/mol, the latter value in accord with D0(Fe+-NH) = 61 +/- 5 kcal/mol obtained from photodissociation.The high bond strength for VNH+ indicates multiple bonding, analogous to that in the isoelectronic VO+, while the weaker bond strength for FeNH+ indicates a single bond, analogous to that in the isoelectronic FeO+.Proton-transfer experiments indicate PA(VN) = 220 +/- 4 kcal/mol from which ΔHf(VN) = 111 +/- 9 kcal/mol and D0(V-N) = 125 +/- 9 kcal/mol are obtained.VNH+ is unreactive with ethene and benzene, but FeNH+ transfers NH to ethene and benzene through metathesis and homologation reactions.A cyclic metalloaminobutane intermediate is consistent with the products of the FeNH+/ethene reaction.

The electronic structures of 2-tetrazenes 1-4 have been studied by UV photoelectron spectroscopy and MNDO calculations.Gas-phase thermolyses of these compounds were investigated by variable temperature PES.We found that the relative stabilities of cyclic 2-tetrazenes strongly depend on ring-size.The total bond order of the N=N bonds can be correlated with the energy differences of the respective first and second ionization potential.

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Thermolyses of N,N,N',N'-tetramethylethylenediamine(1a),N,N,N',N'-tetraethylethylenediamine (1b) and sym-N,N'-dimethylethylenediamine (1c) at 760-825 deg C have been studied by ultraviolet photoelectron spectroscopy.Although the corresponding N -alkylated aminomethylene radicals were not observed, this study establishes that termolysis of 1a is an efficient route to N-methylenimine (3a); methane, ethane, and ethene are the other major products.Diamine 1b yields, besides ethane, ethene, and propane, heretofore unreported N-ethylmethylenimine (3b).Diamine 1c yields imine 3a and methylenimine (3c), as well as hydrogen, methane, ethane, ethene.Molecular orbital eigenvalues of the imines are calculated using HAM/3, MNDO, HF/STO-3G, HF/3-21* methods.