Sieric effects

In fact, chiral ligands are often used in synthesizing molecules of this type, both for observing sieric effects and for aid in solving the X-ray crystal structures. See the discussion of absolute configuration of the previous complex with C.N. = 5 and octahedral complexes with C.N. = 6 (page 495). 

Ethylenediamine and ammonia are almost identical in field strengths (their / factors differ by less than 3%, Chapter I IK and so the LFSE for complexes with the same metal ion will be almost identical. However, ethylenediamine is also a stronger base than ammonia from the inductive effect of the methylene groups. In addition there may be enthalpy differences in the form of ring strain or other sieric effects. See Table 12.6 and the following discussion. 

Other effects are likely to influence emulsion viscosity, particularly high-intemal-phase-ratio emulsions in which the drops sae separated by thin films. Both dynamic phenomena such as streaming potential or interfacial viscosity retardation could take place at the drainage rate of these films. Electrical and sieric repulsion, as well as surface hydration, are probably also important in these kind.s of emulsions. These phenomena, that are due to the pre.scnce of adsorbed. surfactant onto approaching interfaces, have been studied in relation to stability problems but not for their effect on viscosity. However, it can be said as a rule of thumb ihai any effect that would tend to reduce the flow of inlerdrop film would result in increased viscosity or, rather, in impaired flowing ability. 

FIGURE 5.28. (a) Steric hindrance to approach of a nucleophile in propene oxide (b) lack of sieric hindrance in analogous approach to a propene n complex (c) polarization of the n MO in propene by the inductive effect of methyl (d) a symmetric structure of a propene n complex. 

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