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Abstract: The structure of 4-hydroxy-1-methylpiperidinium perchlorate has been characterized by X-ray diffraction, FTIR, Raman and NMR spectroscopies, and by DFT calculations. The crystals belong to orthorhombic Pbca group. The piperidine ring has a chair conformation with the hydroxyl and methyl groups in the equatorial positions. The hydroxyl group interacts by bifurcated O–H···O hydrogen bonds with the ClO4 − anion of 2.905(5) and 3.045(5)Å. Two optimized structures of the title compound have been calculated by the B3LYP/6–31G(d,p) approach. In one of them the anion is involved in the N+–H···O hydrogen bonds of 2.629Å, while in the other the anion interacts electrostatically with the N+ atom of the 4-hydroxy-1-methylpiperidinium cation. In aqueous solution two 4-hydroxy-1-methylpiperidinium perchlorates are in the conformational equilibrium. Their conformations are discussed on the basis of the NMR spectra. The solid state FTIR spectrum is consistent with the X-ray data. [Copyright &y& Elsevier]

• Structure of 8 - hydroxyquinoline betaine monohydrate was solved by X-ray. • The one proton of disordered water molecules is shared between two half-occupied sides. • Three broad bands classify the FTIR spectrum as the ABC type. • PED are used to assign the bands in the vibrational spectrum. • Hirshfeld surface, Mulliken atomic charges, MEP, HOMO-LUMO were computed. • The assignment of 1H and 13C resonance signals are based on the 2D measurements. Molecular structure and properties of 8-hydroxyquinoline betaine monohydrate (1-carboxymethyl-8-hydroxyquinolinium inert salt monohydrate) were studied by X-ray diffraction, DFT calculations, FTIR and NMR spectra. In the crystals, 8-hydroxyquinoline betaine and water are bonded by an intermolecular and asymmetric COO···H 2 O hydrogen bond of 2.782(3) Å. The water molecules are disordered so that one of the proton is shared between two half occupied sites. The hydroxyl group of quinoline is bonded to the neighboring molecule by the O−H···OOC hydrogen bond of 2.571(3) Å. The molecular geometry, Hirshfeld surface, Mulliken atomic charge distribution, molecular electrostatic potential, frontier molecular orbitals, vibrational wavenumbers, magnetic isotropic shielding constants were determined using the density functional theory (DFT/B3LYP) with 6–311++G(d,p) basis set. The FTIR spectrum shows a characteristic ABC structure, typical of medium-short hydrogen bonds. The potential energy distribution (PED) was used to assign the bands in the vibrational spectrum. 1H and 13C NMR spectra were analyzed. [Display omitted] [ABSTRACT FROM AUTHOR]

The complex of 2-(hydroxymethyl)-1-methyl-piperidine [2-(1-methyl-piperidine)-methanol] (MPMe) and p -hydroxybenzoic acid (HBA) crystallizes as a hydrate. HBA interacts through the OH···O and NH···O hydrogen bonds with MPMe. The water mediated hydrogen-bonded bridge molecules MPMe and HBA. The structure of 2-(hydroxymethyl)-1-methyl-piperidinium p -hydroxybenzoate hydrate has been characterized by X-ray diffraction, FTIR and NMR spectroscopy and optimized at the B3LYP/6-311++G(d,p) level of theory. The potential energy distributions, PED, have been used to assign the vibrational spectra. The GIAO/B3LYP/6-311++G(d,p) calculated magnetic isotropic shielding constants have been used to interpret the chemical shifts in the 1 H and 13 C NMR spectra. [ABSTRACT FROM AUTHOR]

• 5-(Quinolinium)-valeric acid bromide hydrates form centrosymmetric and asymmetric dimers. • Water is a bridge between 5-(quinolinium)-valeric acid cations and bromide anions. • The DFT calculations were used to optimize isolated structures of monomer and dimer. • PED are used to assign the bands in the vibrational spectrum. • The NBO, MEP and QTAIM methods were used to characterize the optimized structures. The molecular structure and properties of 5-(quinolinium)-valeric acid bromide monohydrate are characterized by X-ray diffraction, B3LYP/6–311++G(d,p) calculations, FTIR and NMR spectra. Two molecules of this compound are hydrogen bonded through two water molecules and two bromide anions into centrosymmetric dimers, which are arranged in a strongly anisotropic layered structure. The structures of monomer and dimer of the title complex are optimized at the B3LYP/6–311++G(d,p) level of theory. The conformations of the valeric acid unit in the crystalline monohydrate and in isolated molecules (monohydrates and anhydrous forms) are compared. The experimental and theoretical infrared spectra are discussed. The FTIR spectrum shows an absorption in the 3500–2700 cm−1 region attributed to the νCOOH···OH 2 and νBr−···H 2 O. The potential energy distributions (PED) are used to assign bands in the IR spectrum of the monomer. The 1H and 13C NMR chemical shifts are assigned by two-dimensional techniques, COSY, HSQC and HMBC. Charge delocalization is analyzed using the natural bond orbital (NBO) method and it is shown in molecular electrostatic potential (MEP) maps. The bent conformations of the computed structures are characterized by the QTAIM method. Image, graphical abstract [ABSTRACT FROM AUTHOR]

N- Methylpyrrolidine betaine (N- carboxymethyl- N- methyl-pyrrolidinium, inner salt, MPRB) cocrystallizes with p -hydroxybenzoic acid (HBA) at the 1:1 ratio. The complex is characterized by single-crystal X-ray diffraction, FTIR and NMR spectra. The pyrrolidinium ring adopts an envelope conformation with the methyl group in axial and the carboxymethyl substituent in the equatorial positions. In the cocrystal the COO⋯HO and COO⋯HOOC hydrogen bonds are of 2.574 (4) and 2.586 (4) Å, respectively. The molecular geometry, Hirshfeld surface, natural bond orbitals (NBO), molecular electrostatic potential (MEP), vibrational wavenumbers, magnetic isotropic shielding constants were performed using the density functional theory (DFT/B3LYP) with 6–311++G (d,p) basis set. The molecular structures of isolated 1:1 and 1:2 complexes were optimized. The potential energy distribution (PED) of the IR vibrational modes were used to assign the bands in the IR spectrum. Diagrams of the HOMO and LUMO of components and complex are presented. Theoretical and experimental results are in a good agreement. Image 1 • The 1:1 complex of N-methylpyrrolidine betaine with p -hydroxybenzoic acid was prepared. • Structure of complexes were characterized by X-ray diffraction, FTIR and NMR spectra. • The structures of 1:1 and 1:2 complexes were optimized by the B3LYP/6-311++G(d,p) approach. • The molecules are linked through the OH∙∙∙OOC and COOH∙∙∙OOC hydrogen-bonds. • The IR and NMR experimental and computed spectra were discussed. [ABSTRACT FROM AUTHOR]