1,721,327 research outputs found
2,6-Dibromo-3,5-dimethylpyridine and 2,6-diiodo-3,5-dimethylpyridine
No full textThe title compounds 2,6-dibromo-3,5-dimethyl-pyridine, C7H7Br2N, (I), and 2,6-diiodo-3,5-dimethyl-pyridine, C7H7I2N, (II), constitute the first structurally characterized examples of 2,6-dihalo-3,5-dimethyl-pyridines. Compound (I) crystallizes as a racemic twin with two symmetry-independent molecules in the asymmetric unit, while (II) is non-planar with the pyridine ring slightly deformed into a saddle shape, and exhibits crystallographically imposed twofold symmetry. Both (I) and (II) exhibit aromatic face-to-face pi-stacking in the solid state, although there are no other long-range inter-actions. In (I), alternate molecules are oriented at 90 degrees, resulting in X-shaped columns, while in (II), molecules pack in a parallel fashion, leading to a zigzag array
Metal complexes with 'pincer'-type ligands incorporating N-heterocyclic carbene functionalities
No full textThe coordination and organometallic chemistry of linear, rigid, tridentate ligands, which incorporate at least one N-heterocyclic carbene and other ‘classical’ donors, is reviewed across the periodic table with emphasis on unique features due to the presence of the N-heterocyclic carbene donor.<br/
A method for the synthesis of nickel(0) bis(carbene) complexes
No full textA new method leading to Ni(NHC)2 (NHC = IMes, IPri,
SIPri, SIBut) complexes in moderate to good yields, involves
the reaction of NHC (pre-formed or generated in situ) with
Ni(CH3)2(tmed), tmed = N,N-tetramethylethylenediamine;
in one case, the intermediate Ni[I(Me2)Pri]2(CH3)2, I(Me2)Pri =
N,N-diisopropyl-4,5-dimethylimidazol-2-ylidene, has been
isolated and structurally characterised
Trends in components of sea level around the English Channel
No full textThe longest available records of hourly sea level data have been analysed for six ports around
the English Channel. The quality of the data is extremely variable with the longest and most
reliable records belonging to Brest and Newlyn. A separate analysis of the components of sea
level: mean sea level, tides and meteorological residuals (surges), is used. Results show a
general increase in mean sea level throughout the period of observation. The various tidal
constituents show interesting local short-term variations in amplitude and phase but no longterm
trends. There is no evidence of an increase in weather effects on sea levels over the
period analysed. De-trended sea level and pressure values show annual sea level fall as annual
air pressures increase, as expected for the inverse barometer response. Meteorological
residuals were compared to North Atlantic Oscillation (NAO) index values. The correlations
are in general very small, especially for the annual mean NAO values. However correlations
are slightly more apparent for the annual winter mean NAO values
Sea level variability and its impacts in a NW European lagoon: Ria de Aveiro, Portugal
No full textSea level variation is a main contributor in controlling the evolution of coastal lagoons as well as determining risks of coastal flooding. This work investigates both long and short-term sea level variability in the Ria de Aveiro, a tide-dominated shallow coastal lagoon located on the western coast of Portugal. The 27 year series of available sea level observations from the permanent tide gauge, at the mouth of the Lagoon, has been analyzed for changes in the different sea level components: tides, surges and mean sea level. The various tidal constituents show interesting local short-term variations in amplitude and phase but no long-term trends. There is no evidence of an increase in weather effects on sea levels and of mean sea level over the period analyzed. Short (1-3 month) sea level data collected during two surveys (1987/8 and 2002/3) in the lagoon are compared. Results show that there has been a significant change in the tidal characteristics of the Lagoon with a general increase in amplitude and decrease in phase for most harmonic constituents
Alterações do nível do mar associadas à variabilidade climática na costa NE Atlântica
No full textTrends in long-term sea level records associated to climate variability, along the NW European coast, are analysed by looking separately at the three principal sea level components; mean sea level, tides and meteorological residuals. A rise in mean sea level is confirmed for all the ports analysed. The hydrodynamic consequences of future sea level variability in the Portuguese estuarine system of the Ria de Aveiro are assessed, illustrating the importance of sea level studies. Pressure data collected show that there has been an increase in amplitude and a decrease in phase for most tidal constituents over the last 16 years
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