Carbonyl group orienting effect

A profound effect on the electronic asymmetry of the dimer has been detected for site-directed mutants of R. sphaeroides in which hydrogen bonds to the carbonyl groups of the BChl are either broken or formed.69 71 The H-bond effect can be traced back to the electrostatic interaction between the oriented dipole of... 

Furthermore, the oxygen atom of the carbonyl group in the amide function has an electron pair oriented antiperiplanar to the polar C-N bond there is therefore an electronic delocalization caused by the overlap of that oxygen electron pair orbital with the antibonding orbital of the C-N sigma bond (o ) as shown in two dimensions by structure 5 and in three dimensions by structure . This additional n-o delocalization is referred to here as a secondary electronic delocalization. Thus, amides are similar to esters because they both have the primary electronic effect and one secondary electronic effect. This is in contrast with Z esters which have two secondary electronic effects besides the primary electronic effect. 

The presence of bulky alkyl groups results in a shift of half-wave potentials towards more negative values this effect is interpreted rather as a hindrance of the attainment of the optimum conformation in the transition state than as a direct hindrance of the approach of the electron. An example is provided by the w-alkyl-substituted acetophenones (72). When one of the substituents is a phenyl group (68), the steric effects are much less pronounced, probably because the phenyl groups are orientated plane-parallel to the electrode surface, which forces the remaining alkyl groups into an orientation away from the electrode, where they cannot interfere with the orientation of the carbonyl group. 

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