X-ray Structure of a Trimeric 5,5′-Biaryl/erythro--O-4-ether Lignin Model: Evidence for Through-Space Weak Interactions

Abstract

The crystal structure of a trimeric lignin model 1 presenting the characteristic pattern of biphenyl (5,5') and aryl-alkyl-ether (beta-O-4) linkages has been determined. The crystal system is triclinic and the crystallographic unit cell consists of two monomeric molecules. These results are compared with crystal data from the literature of simple models of the 5,5' and beta-O-4 structure type. The availability of a terminal aldehyde function on the model affords some interesting intermolecular interactions by weak hydrogen bonding which controls the conformation of the molecule and the aromatic ring orientation in particular; an unexpected cisoïd conformation of the biaryl unit is observed based on the 64.4 degrees value found for the torsion angle between the two 5,5' aromatic rings.

Miscible Blends of Kraft Lignin Derivatives with Low-TgPolymers

“…44 Such a situation has been encountered in the crystal structures of divanillyltetrahydrofuran 45 and a 5-5′,8-O-4′′ linked trilignol derivative. 46 On the other hand, when nonbonded orbital interactions fail to compensate for π-electron repulsion, face-to-face placement of two aromatic rings is unfavor- able; instead, there is a continuum of favorable geometries extending from a parallel offset arrangement to an edge-on relationship. 47 The former is essentially what prevails at ∼4.6 Å intermolecular separation distances in the crystal structure of a typical (phenolic) 8-5′ linked dilignol, 48 while the latter is a reasonable representation of what occurs at ∼5.3 Å intermolecular separations in the crystal structure of a standard (nonphenolic) 8-O-4′ linked dilignol.…”

“…On one hand, nonbonded orbital interactions will be significant between cofacial aromatic rings that descend to an energy minimum at small (≤3.4 Å) separation distances . Such a situation has been encountered in the crystal structures of divanillyltetrahydrofuran and a 5−5‘,8− O − 4‘ ‘ linked trilignol derivative . On the other hand, when nonbonded orbital interactions fail to compensate for π-electron repulsion, face-to-face placement of two aromatic rings is unfavorable; instead, there is a continuum of favorable geometries extending from a parallel offset arrangement to an edge-on relationship .…”

Dynamic Moisture Sorption Characteristics of Xerogels from Water-Swellable Oligo(oxyethylene) Lignin Derivatives

“…25,43 Sorption hysteresis in rigid sorbents such as lignin can be attributed to the irreversible deformation of the sorbent molecules during adsorption, 43 initially described by Tvardovski et al 47 for clay minerals and also discussed for aromatic compounds such as humic acids. 48 This swellingconnected with the cleavage of weaker interstructural bonds of lignin formed by hydrophobic interactions and hydrogen bonds 49  precedes diffusion, which continues into newly formed pores in the sorbent 43 and is additionally enforced because of the thermal motion of the sorbate. 50 Another explanation connects sorption hysteresis with the formation of metastable states of the adsorbate in pores, i.e., capillary condensation in mesopores 23 in the region of intermediate and high a w .…”

Styrene-Spaced Copolymers Including Anthraquinone and β-O-4 Lignin Model Units: Synthesis, Characterization and Reactivity Under Alkaline Pulping Conditions

“…The main barrier to research progress was that delignification mechanisms were difficult to be studied directly. The structural complexity of lignins associated with its structural heterogeneity make the mechanism investigations rather difficult. , Consequently, major advances on lignin reactivity have been performed on well-defined lignin models, − which are designed to mimic the chemical and physical properties of natural lignins. A large variety of lignin model compounds has been reported, particularly the so-called dimeric β-O-4 derivatives, which mimic the major subunits of the native lignin macromolecular structure. , Nevertheless, lignin model compounds may not completely accurately represent the interactions in native lignin because the inherent complexity of the biopolymer.…”