Magdalena Sałdyka

Cis–trans isomerism of the keto tautomer of formohydroxamic acid

Abstract The trans (1E) isomer of the formohydroxamic acid is identified for the first time and the population ratio of the trans (1E) and cis (1Z) isomers is estimated to be 0.035±0.009 in the gas phase at room temperature on the basis of the matrix infrared isolation spectroscopy.

Photodecomposition of formohydroxamic acid. Matrix isolation FTIR and DFT studies

Primary dissociation pathways of formohydroxamic acid have been investigated in argon and xenon matrices. The irradiation of the HCONHOH/Ar(Xe) matrices with full output of an Xe arc lamp leads to the formation of hydrogen bonded HNCO–H2O and NH2OH–CO complexes. Two structures were identified for the isocyanic acid–water complex, in the first one HNCO is hydrogen bonded to an oxygen atom of the water molecule and in the second, water serves as a proton donor toward the nitrogen atom of HNCO. For the hydroxylamine–carbon monoxide complex the spectra prove the existence of the structure with the OH group attached to the carbon atom and also suggest the existence of the structure with the NH2 group interacting with the carbon atom. The identification of the products is confirmed by 15N isotopic substitution and by DFT calculations (at the B3LYP level of the theory with 6-311++G(2d,2p) basis set) of the structure and vibrational frequencies of the identified complexes.

Isomerical and structural determination of N-hydroxyurea: a matrix isolation and theoretical study.

The structure, isomerization pathways and vibrational spectra of the important N-hydroxyurea (HU) molecule were studied by matrix isolation FT-IR spectroscopy and molecular orbital calculations undertaken at the MP2/6-311++G(2d,2p) level of theory. In agreement with theoretical predictions, 1Ea represents the most stable keto isomer in the gas-phase, being the dominant species trapped in argon matrices, while the 1Za isomer also contributes to the spectrum of isolated HU molecules. According to the calculated abundance values at the temperature of evaporation of the compound (393 K), the 1Ea and 1Za isomers together with a small contribution of 1Eb are expected to appear in the experimental spectra. Since the barrier for interconversion 1Ea↔ 1Eb is only ∼2 kJ mol(-1), these two isomers are in equilibrium in the matrices and, at low temperature, the population of the less stable 1Eb form is too small to be observed. Full assignment of the observed spectra of N-hydroxyurea and its deuterium analogue was undertaken on the basis of comparison with theoretical data.

Structural and spectroscopic characterization of DMF complexes with nitrogen, carbon dioxide, ammonia and water. Infrared matrix isolation and theoretical studies

An infrared spectroscopic and MP2/6-311++G(2d,2p) study of the complexes between N,N-dimethylformamide (DMF) and nitrogen, carbon monoxide, water, ammonia trapped in solid argon matrices is reported [corrected]. The 1:1 molecular complexes have been identified in the DMF/B/Ar matrices (B=N2, CO, H2O, NH3); their structures were determined by comparison of the spectra with the results of calculations. The analysis of the experimental and theoretical data indicate that the DMF-N2, CO complexes present in the matrices are stabilized by (C=)O⋯N and (C=)O⋯C van der Waals interactions. In turn, in the DMF-H2O, NH3 complexes the (C=)O⋯H(OH) and (C=)O⋯H(NH2) hydrogen bonding is present in which the carbonyl group of DMF acts as a proton acceptor. In all systems studied the C-H⋯X (X=N, C, O) bonding is a second intermolecular force stabilizing the planar complexes. Some spectral features indicate that for DMF-H2O, DMF-NH3 systems the nonplanar structures with the C=O⋯H interaction are also present. The study demonstrated the strong sensitivity of the CH stretching wavenumber to an involvement of the C-H and/or C=O groups of DMF in an intermolecular interaction.

Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride.

An infrared spectroscopic and MP2/6-311++G(2d,2p) study of hydrogen bonded complexes of formaldoxime with ammonia and hydrogen chloride trapped in solid argon matrices is reported. Both 1:1 and 1:2 complexes between formaldoxime and ammonia, hydrogen chloride have been identified in the CH2NOH/NH3/Ar, CH2NOH/HCl/Ar matrices, respectively, their structures were determined by comparison of the spectra with the results of calculations. In the 1:1 complexes present in the argon matrices the OH group of formaldoxime acts as a proton donor for ammonia and the nitrogen atom acts as a proton acceptor for hydrogen chloride. In the 1:2 complexes ammonia or hydrogen chloride dimers interact both with the OH group and the nitrogen atom of CH2NOH to form seven membered cyclic structures stabilized by three hydrogen bonds. The theoretical spectra generally agree well with the experimental ones, but they seriously underestimate the shift of the OH stretch for the 1:1 CH2NOH⋯NH3 complex.

Photodecomposition of N-hydroxyurea in argon matrices. FTIR and theoretical studies

The photochemistry of N-hydroxyurea in solid argon has been investigated by FTIR and ab initio calculations. The irradiation of the NH2CONHOH/Ar matrices with the full output of the Xe arc lamp leads to the formation of the HNCO–NH2OH and N2–H2O–CO complexes. For the isocyanic acid–hydroxylamine complex, the spectra prove the existence of the hydrogen bonded structure with the NH group of HNCO attached to the oxygen atom of the NH2OH molecule. Two structures were identified for the nitrogen–water–carbon monoxide complex. In the first one, water is hydrogen bonded to the carbon atom and interacts with the nitrogen atom through van der Waals forces. In the second structure, water serves as a proton donor toward the nitrogen and carbon atoms of N2 and CO molecules, respectively. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structure and vibrational spectra of the identified complexes.

Photochemistry of Acetohydroxamic Acid in Solid Argon. FTIR and Theoretical Studies

The products formed during exposure of the CH3CONHOH/Ar (AHA/Ar) matrices to the full output of the Xe lamp and to 225 nm OPO radiation are studied. The irradiation promotes the isomerization, 1Z → 1E, and AHA photodissociation reactions. Four pairs of coproducts are experimentally found to appear in the photolysis, they form the complexes: CH3OH···HNCO (1), H2O···CH3NCO (2), H2O···CH3CNO (3) and CO···CH3NHOH (4). The structures of the complexes were optimized at the MP2 computational level with the 6-311++G(2d,2p) and aug-cc-pVTZ basis sets. Three local minima were predicted for the complex (1), two for the complexes (2) and (3) and four local minima were found for the complex (4). The comparison of the theoretical spectra with the experimental ones allowed us to determine the structures of the complexes formed in the matrix. The mechanisms of the reaction channels leading to formation of the four coproducts are proposed. It is concluded that the first step in formation of the (1), (2) and (3) complexes is the scission of the N-O bond whereas the creation of the complex (4) is due to the cleavage of the C-N bond.