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ABSTRACT:Hard and softwood and wood constituent polymers (cellulose and lignin) were studied using Fourier transform infrared (FTIR) spectroscopy. The hollocelluloseto-lignin ratio was estimated for some of the timber species. The structural difference between Klason lignin isolated from softwood (Pinus roxberghii and cupressus lusitanica) and hard wood (Acacia auriculaeformis and Eucalyptus tereticornis) species was studied.

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Recent theoretical studies are reviewed which show that the naked group 14 atoms E = C-Pb in the singlet (1)D state behave as bidentate Lewis acids that strongly bind two σ donor ligands L in the donor-acceptor complexes L→E←L. Tetrylones EL2 are divalent E(0) compounds which possess two lone pairs at E. The unique electronic structure of tetrylones (carbones, silylones, germylones, stannylones, plumbylones) clearly distinguishes them from tetrylenes ER2 (carbenes, silylenes, germylenes, stannylenes, plumbylenes) which have electron-sharing bonds R-E-R and only one lone pair at atom E. The different electronic structures of tetrylones and tetrylenes are revealed by charge- and energy decomposition analyses and they become obvious experimentally by a distinctively different chemical reactivity. The unusual structures and chemical behaviour of tetrylones EL2 can be understood in terms of the donor-acceptor interactions L→E←L. Tetrylones are potential donor ligands in main group compounds and transition metal complexes which are experimentally not yet known. The review also introduces theoretical studies of transition metal complexes [TM]-E which carry naked tetrele atoms E = C-Sn as ligands. The bonding analyses suggest that the group-14 atoms bind in the (3)P reference state to the transition metal in a combination of σ and π∥ electron-sharing bonds TM-E and π⊥ backdonation TM→E. The unique bonding situation of the tetrele complexes [TM]-E makes them suitable ligands in adducts with Lewis acids. Theoretical studies of [TM]-E→W(CO)5 predict that such species may becomes synthesized.

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The equilibrium geometries and bond dissociation energies of 16VE and 18VE complexes of ruthenium and iron with a naked carbon ligand are reported using density functional theory at the BP86/TZ2P level. Bond energies were also calculated at CCSD(T) using TZ2P quality basis sets. The calculations of [Cl2(PMe3)2Ru(C)] (1Ru), [Cl2(PMe3)2Fe(C)] (1Fe), [(CO)2(PMe3)2Ru(C)] (2Ru), [(CO)2(PMe3)2Fe(C)] (2Fe), [(CO)4Ru(C)] (3Ru), and [(CO)4Fe(C)] (3Fe) show that 1Ru has a very strong Ru-C bond which is stronger than the Fe-C bond in 1Fe. The metal-carbon bonds in the 18VE complexes 2Ru-3Fe are weaker than those in the 16VE species. Calculations of the related carbonyl complexes [(PMe3)2Cl2Ru(CO)] (4Ru), [(PMe3)2Cl2Fe(CO)] (4Fe), [(PMe3)2Ru(CO)3] (5Ru), [(PMe3)2Fe(CO)3] (5Fe), [Ru(CO)5] (6Ru), and [Fe(CO)5] (6Fe) show that the metal-CO bonds are much weaker than the metal-C bonds. The 18VE iron complexes have a larger BDE than the 18VE ruthenium complexes, while the opposite trend is calculated for the 16VE compounds. Charge and energy decomposition analyses (EDA) have been carried out for the calculated compounds. The Ru-C and Fe-C bonds in 1Ru and 1Fe are best described in terms of two electron-sharing bonds with sigma and pi symmetry and one donor-acceptor pi bond. The bonding situation in the 18 VE complexes 2Ru-3Fe is better described in terms of closed shell donor-acceptor interactions in accordance with the Dewar-Chatt-Duncanson model. The bonding analysis clearly shows that the 16VE carbon complexes 1Ru and 1Fe are much more strongly stabilized by metal-C sigma interactions than the 18VE complexes which is probably the reason why the substituted homologue of 1Ru could become isolated. The EDA calculations show that the nature of the TM-C and TM-CO binding interactions resembles each other. The absolute values for the energy terms which contribute to Delta(Eint) are much larger for the carbon complexes than for the carbonyl complexes, but the relative strengths of the energy terms are not very different from each other. The pi bonding contribution to the orbital interactions in the carbon complexes is always stronger than sigma bonding. There is no particular bonding component which is responsible for the reversal of the relative bond dissociation energies of the Ru and Fe complexes when one goes from the 16VE complexes to the 18VE species. That the 18 VE compounds have longer and weaker TM-C and TM-CO bonds than the respective 16 VE compounds holds for all complexes. This is because the LUMO in the 16 VE species is a sigma-antibonding orbital which becomes occupied in the 18 VE species.

The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform the Parties to the Montreal Protocol. The EEAP focuses on the effects of UV radiation on human health, terrestrial and aquatic ecosystems, air quality, and materials, as well as on the interactive effects of UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than previously held. Because of the Montreal Protocol, there are now indications of the beginnings of a recovery of stratospheric ozone, although the time required to reach levels like those before the 1960s is still uncertain, particularly as the effects of stratospheric ozone on climate change and vice versa, are not yet fully understood. Some regions will likely receive enhanced levels of UV radiation, while other areas will likely experience a reduction in UV radiation as ozone- and climate-driven changes affect the amounts of UV radiation reaching the Earth's surface. Like the other Panels, the EEAP produces detailed Quadrennial Reports every four years; the most recent was published as a series of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). In the years in between, the EEAP produces less detailed and shorter Update Reports of recent and relevant scientific findings. The most recent of these was for 2016 (Photochem. Photobiol. Sci., 2017, 16, 107-145). The present 2017 Update Report assesses some of the highlights and new insights about the interactive nature of the direct and indirect effects of UV radiation, atmospheric processes, and climate change. A full 2018 Quadrennial Assessment, will be made available in 2018/2019.

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