Next page second generation

A -Heterocyclic carbenes (24.64) have become important ligands in organometallic chemistry, notable examples being Grubbs second and third generation catalysts. Synthetic routes to A -heterocyclic carbene complexes (which are stable to air) typically involve salt metathesis or elimination reactions. Reaction 24.103 shows the use of a 1,3-dialkylimidazolium salt as a precursor, and scheme 24.104 illustrates conversions relevant to Grubbs catalysts (see next page). 

On pages 92 to 98 tliie distribution of velocity and its accompanying momentum flux in a flowing stream in turbulent flow through a pipe was described. Three rather ill-defined zones in the cross section of the pipe were identified. In the first, immediately next to the wall, eddies are rare, and momentum flow occurs almost entirely by viscosity in the second, a mixed regime of combined viscous and turbulent momentum transfer occurs in the main part of the stream, which occupies the bulk of the cross section of the stream, only the momentum flow generated by the Reynolds stresses of turbulent flow is important. The three zones are called the viscous sublayer, the buffer zone, and the turbulent core, respectively. 

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