Lignin is by far the most abundant substance based on aromatic moieties in nature, and the largest contributor to soil organic matter. Millions of tonnes of several lignin preparations are produced by the paper industry every year, and a minimal amount of lignin is isolated by direct extraction of lignin from plants. Lignin is used either directly or chemically modified, as a binder, dispersant agent for pesticides, emulsifier, heavy metal sequestrant, or component for composites and copolymers. For value-added applications of lignin to be improved, medium- and long-term conversion technologies must be developed, especially for the preparation of low-molecular-weight compounds as an alternative to the petrochemical industry.

Atoms in Molecules Theory has been applied to analyze bonding properties, in potentially hypervalent pnicogen (N, P or As)−chalcogen(O or S) bonds within the framework of three plausible models:  (i) one σ bond and two π back-bonds (negative hyperconjugation), (ii) one σ bond and three π back-bonds, and (iii) three Ω (banana) bonds. The topological analyses (based upon the electron charge density (ρ(r)), its Laplacian (∇2ρ(r)), bond ellipticity, etc.) and the charges were consistent with a highly polarized σ bond, with bond strength dependent on the electrostatic interactions. The equilibrium geometries were optimized by both density functional theory with a hybrid functional (B3LYP) and by ab initio methods at the MP2(full) level, using the 6-311G basis set augmented by polarization and/or diffuse functions.

Chemical reactions and many of the procedures of separation and purification employed in industry, research or chemistry teaching utilize solvents massively. In the last decades, with the birth of Green Chemistry, concerns about the employment of solvents and the effects on human health, as well as its environmental impacts and its dependence on non-renewable raw materials for manufacturing most of them, has drawn the attention of the scientific community. In this work, we review the concept of green solvent and the properties and characteristics to be considered green. Additionally, we discuss the different possible routes to prepare many solvents from biomass, as an alternative way to those methods currently applied in the petrochemical industry.

The electron pair density in conjunction with the AIM theory and calculated NMR chemical shifts were used to characterize the bonding properties for nine pnicogen and chalcogen ylide structures. The hybrid B3LYP and MP2 methods were employed with the 6-311+G* basis set. No evidence was found to support a banana (Ω) bonding scheme. Instead, different bonding schemes were found to be dependent on the electronegativity of the X atom in the C-X bond. When X is a highly electronegative atom (N,O), the C-X bond is weaker than a single bond, due to electrostatic repulsion. When the X atom has electronegativity similar to carbon, a covalent, yet significantly polar interaction results, and its strength is determined mainly by electrostatic interactions, with a small contribution of negative hyperconjugation.