Crystal structure of Schiff base derivative of 2,2′-dihydroxybiphenyl-3-carbaldehyde with n-butylamine

Schiff Bases and Stereocontrolled Formation of Fused 1,3-Oxazolidines from 1-Amino-2-Indanol: A Systematic Study on Structure and Mechanism

This paper thoroughly explores the formation of Schiff bases derived from salicylaldehydes and a conformationally restricted amino alcohol (1-amino-2-indanol), as well as the generation of 1,3-oxazolidines, a key heterocyclic core present in numerous bioactive compounds. We provide enough evidences, both experimental-including crystallographic analyses and DFT-based calculations on imine/enamine tautomerism in the solid state and solution. In the course of imine formation, a pentacyclic oxazolidine-oxazine structure could be isolated with complete stereocontrol, whose configuration has been determined by merging theory and experiment. Mechanistic studies reveal that, although oxazolidines can be obtained under kinetic conditions, the prevalence of imines obeys to thermodynamic control as they are the most stable structures. The stereochemical outcome of imine cyclization under acylating conditions leads to formation of 2,4-trans-oxazolidines.

Molecular structure, quantum mechanical calculation and radical scavenging activities of (E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3-methoxyphenol and (E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)methyl]-3-methoxyphenol compounds

In this study, (E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3-methoxyphenol and (E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)methyl]-3-methoxyphenol compounds have been synthesized and characterized by using X-ray crystallographic method, FT-IR and Density functional method. The molecular geometry, vibrational frequencies of the title compounds in the ground state have been calculated by using B3LYP with the 6-31G(d,p) basis set. The tautomeric form of the compounds has been demonstrated by using single crystal X-ray method, FT-IR spectrometer and DFT method. In addition, HOMO-LUMO energy gap, molecular electrostatic potential map and NBO analysis of the compounds are performed at B3LYP/6-31G(d,p) level. It may be remarked that the free radical scavenging activities of the title compounds were assessed using DPPH, DMPD+, and ABTS+ assays. The obtained results show that especially compound 2 has effective DPPH (SC50 1.52±0.14 μg/mL), DMPD+ (SC50 1.22±0.21 μg/mL), and ABTS+ (SC50 3.32±0.17 μg/mL) scavenging activities compared with standards (BHA, rutin, and trolox).

Molecular structure, spectroscopic investigations, second-order nonlinear optical properties and intramolecular proton transfer of (E)-5-(diethylamino)-2-[(4-propylphenylimino)methyl]phenol: a combined experimental and theoretical study

This work presents a combined experimental and theoretical study on an ortho-hydroxy Schiff base compound, (E)-5-(diethylamino)-2-[(4-propylphenylimino)methyl]phenol. The crystal structure and spectroscopic properties of the compound have been determined by using X-ray diffraction, IR and UV-vis spectroscopy techniques. The electronic structure, vibrational frequencies and electronic absorption spectra have been investigated from the calculative point of view. A relaxed potential energy surface scan has been performed based on the optimized geometry of OH tautomeric form to describe the potential energy barrier belonging to intramolecular proton transfer and to observe the effects of transfer on the molecular geometry. The second-order nonlinear optical properties have been investigated based on the first static hyperpolarizability (β) by using the density functional theory.

N,N'-Bis[(2-hydroxy-phen-yl)(phen-yl)methyl-idene]propane-1,2-diamine

In the the title compound, C(29)H(26)N(2)O(2), two strong intra-molecular O-H⋯N hydrogen bonds involving the hydr-oxy and imine groups generate S(6) ring motifs. The dihedral angles between the pairs of terminal benzene rings are 89.8 (2) and 87.8 (2)°.

2,2'-[(Propane-1,3-diyldinitrilo)bis-(phenyl-methyl-idyne)]diphenol

In the title mol­ecule, C₂₉H₂₆N₂O₂, there are two strong intra­molecular O—H⋯N hydrogen bonds involving the hydr­oxy and imine groups, forming S(6) ring motifs. The dihedral angles between adjacent phenyl rings and phenol-containing planes are 85.27 (19) and 91.38 (18)°. In the crystal structure, weak inter­molecular C—H⋯O hydrogen bonds connect mol­ecules into a two-dimensional network.

Zwitterionic 6-methyl-2-oxo-3-[1-(ureido-iminio)eth-yl]-2H-pyran-4-olate monohydrate

The title compound, C(9)H(11)N(3)O(4)·H(2)O, was prepared by the reaction of dehydro-acetic acid and semicarbazide hydro-chloride. It crystallizes in a zwitterionic form with cationic iminium and anionic enolate groups. In the crystal structure, the almost planar mol-ecules are held together by N-H⋯O, O-H⋯O and C-H⋯O hydrogen bonds, some of them involving the water molecules.

The salt-cocrystal continuum: the influence of crystal structure on ionization state

Salts and cocrystals are multicomponent crystals that can be distinguished by the location of the proton between an acid and a base. At the salt end of the spectrum proton transfer is complete, and on the opposite end proton transfer is absent in cocrystals. However, for acid-base complexes with similar pK(a) values, the extent of proton transfer in the solid state is not predictable and a continuum exists between the two extremes. For these systems, both the DeltapK(a) value (pK(a) of base - pK(a) of acid) and the crystalline environment determine the extent of proton transfer. A total of 20 complexes containing theophylline and guest molecules with DeltapK(a) values less than 3 have been prepared, resulting in 13 cocrystals, five salts, and two complexes with mixed ionization states based on IR spectroscopy and single-crystal diffraction data. We propose modifications to the DeltapK(a) rule for selecting salt screen counterions that focus on the discovery of solid forms with useful physical properties rather than an arbitrary cutoff value for DeltapK(a).

Multinuclear magnetic resonance, electrospray ionization–mass spectroscopy, and parametric method 5 studies of a new derivative of gossypol with 2-thiophenecarbohydrazide as well as its complexes with LI+, Na+, K+, RB+, and Cs+ cations

A new derivative of racemic gossypol with 2-thiophenecarbohydrazide (GHHT) and its complexes with monovalent cations have been synthesized and studied by electrospray ionization-mass spectroscopy (ESI-MS), multinuclear nuclear magnetic resonance (NMR), as well as by the Parametric Method 5 (PM5) methods. It is demonstrated that GHHT forms stable complexes of 1:1 stoichiometry with monovalent metal cations. The structures of the complexes are stabilized by three types of intramolecular hydrogen bonds. The spectroscopic methods have provided clear evidence that GHHT and its complexes exist in the DMSO-d6 solution in the N-imine-N-imine tautomeric forms. The structures of the GHHT and its complexes with Li+, Na+, K+, Rb+, and Cs+ cations are visualized and discussed in detail.

The spectroscopic study of hydrogen bonding in some 3,3'-derivatives of 2,2'-bipyridyl

Four 3,3'-derivatives of 2,2'-bipyridyl have been investigated by multinuclear NMR, IR and X-ray methods. In all cases the weak intramolecular hydrogen bonds between exocyclic nitrogen-containing substituent and pyridine-type ring nitrogen atom were found. In contrast to the previous results the nitrogen chemical shifts of pyridine ring atom do not provide valuable information about hydrogen bond strength. The presence of intramolecular hydrogen bonds were confirmed by nitrogen chemical shifts of exocyclic amino and acetamide groups, deuterium isotope effects in the solid state and IR measurements in both chloroform solution and the solid state. The X-ray structures obtained for asymmetric 3-amino-3'-methylamino and 3,3'-diacetamide derivatives confirmed conclusions made on the base of spectral results.