Crystallography and magnetism of radicals with hindered hydroxyl groups: 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl and 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl.
Radicals form networks of OH... ON and OH...Me(nitroxide) interactions. In 2, a frustrated network forms with insufficient N-O units to form extended chain interactions. The magnetism of 1 fits a 1-D Heisenberg model with J/k=-25 J mol(-1), while 2 shows more complex exchange behaviour consistent with its disordered crystal lattice.
Hindered Hydrogen Bonding in 2,6-Di- tert -butylphenols with Para Aza-Heterocyclic Rings
A crystallographic study of several 2,6-di-tert-butylated phenols having 4-azaheterocyclic substituents showed phenolic OH···N hydrogen bonding despite the steric hindrance of the tert-butyl groups, with O(H)···N donor-to-acceptor distances less than 3 A in several cases. The OH···N angles are substantially bent from ideal near-linearity. Infrared spectroscopy in KBr matrixes for some of the tert-butylated systems shows broadened OH stretching bands that are shifted to lower energy than is typical of 2,6-di-tert-butylated phenols. This is consistent with hydrogen bonding, whereas narrow OH stretching bands are more typical for systems such as 2,6-di-tert-butylated phenols that are too sterically hindered for effective phenolic hydrogen bonding. Head-to-tail 1-D chains of phenolic OH···N interactions are present in a number of the crystal lattices. Although the set of studied molecules has limited conformational flexibility to allow for optimizing hydrogen-bond geometry within the constraints of ortho-tert...
Identification of Dihydroxy Aromatic Compounds in a Low-Temperature Pyrolysis Coal Tar by Gas Chromatography−Mass Spectrometry (GC−MS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)
Dihydroxy aromatics in coal tar undergo rapid coupling reactions with each other and with some coal-derived species during coal pyrolysis and liquefaction. However, only limited information on the structure of dihydroxy aromatics is known. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography−mass spectrometry (GC−MS) were used to characterize the dihydroxy aromatics in a low-temperature pyrolyzed coal tar and its distillate and residue fractions. Negative-ion electrospray ionization (ESI) FT-ICR MS spectra of coal-tar-derived samples had low molecular masses and narrow mass ranges. Negative-ion ESI is extremely selective for the dihydroxy aromatics present in coal tar. The O2 class species had the highest ion intensity among the species in the negative-ion FT-ICR mass spectrum for each sample. Dihydroxy compounds with an aromatic core structure of benzene, indan, biphenyl (and/or acenaphthene), and naphthalene were identified in the distillate fract...