Isothermal and isochoric crystallization of highly hygroscopic pyridine N-oxide of aqueous solution

Molecular structure and electron distribution of 4-nitropyridine N-oxide: Experimental and theoretical study of substituent effects

The molecular structure of 4-nitropyridine N-oxide, 4-NO2-PyO, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and by quantum chemical calculations (DFT and MP2). Comparison of these results with those for non-substituted pyridine N-oxide and 4-methylpyridine N-oxide CH3-PyO, demonstrate strong substitution effects on structural parameters and electron density distribution. The presence of the electron-withdrawing -NO2 group in para-position of 4-NO2-PyO results in an increase of the ipso-angle and a decrease of the semipolar bond length r(N→O) in comparison to the non-substituted PyO. The presence of the electron-donating -CH3 group in 4-CH3-PyO leads to opposite structural changes. Electron density distribution in pyridine-N-oxide and its two substituted compounds are discussed in terms of natural bond orbitals (NBO) and quantum theory atoms in molecule (QTAIM).

The molecular structure of 4-methylpyridine-N-oxide: Gas-phase electron diffraction and quantum chemical calculations

The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in C_S molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp² hybridization concept of the nitrogen and carbon atoms in the ring. The experimental geometric parameters are in a good agreement with the parameters for non-substituted N-oxide and reproduced very closely by DFT calculations. The presence of the electron-donating CH₃ substituent in 4-MePyO leads to a decrease of the ipso-angle and to an increase of r(N→O) in comparison with the non-substituted PyO. Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. The nature of the semipolar N→O bond is discussed.

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The molecular structure of 4-methylpiridine-N-oxide has been studied by GED and quantum chemical calculations.

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Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme.

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The molecule possesses C_S symmetry with the planar pyridine ring.

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Obtained molecular parameters confirm the hyperconjugation in the pyridine ring.

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The presence of the electron-donating CH₃ substituent in 4-MePyO results in an increase of r(N→O).

Crystal structure of 3,5-di-methyl-pyridine N-oxide dihydrate

In the title compound, also known as 3,5-lutidine N-oxide dihydrate, C7H9NO·2H2O, the N-O bond is weakened due to the involvement of the O atom as an acceptor of hydrogen bonds from the two water mol-ecules of crystallization present in the asymmetric unit. Fused R35(10) ring motifs based on O-H⋯O hydrogen bonds form chains in the [010] direction, which are further connected by weak C-H⋯O inter-molecular contacts. As a result, the lutidine mol-ecules are stacked in an efficient manner, with π-π contacts characterized by a short separation of 3.569 (1) Å between the benzene rings.

High pressure used for producing a new solvate of 1,4-diazabicyclo[2.2.2]octane hydroiodide

Above 3.1 GPa, the solvate with water and methanol is formed, which cannot be obtained at normal pressure.