Acyl groups, electronic effects

A polarographic study of 4,4-diacyl triafulvenes290 showed that both oxidative and reductive processes may occur, reduction being somewhat favored over oxidation due to mesomeric effects of the acyl grouping [one-electron reduction —1.2 to —1.3 V (475) one-electron oxidation +1.6 to +1.75 V (476)]. 

The reaction may also be considered as acylation of the nucleophile, since an acyl group RCO- is effectively added to the nucleophile this description, however, conceals the fact that the electron-rich nucleophile is actually the attacking species in the reaction. 

It is not easy to determine the differences in structural selectivity among all possible derivatives. A rationalization based on an electronic effect [18] and the length of the acyl substituent on cellulose were attempted [42]. CTA-I (micro-crystalline cellulose triacetate) is very specific and can be used for resolution of racemic compounds both having aromatic rings and carbonyl groups. On the other hand, a CTA-II (cellulose triacetate) CSP has a different selectivity. Both... 

As discussed above, dialkylamino carbene complexes result in the formation of indenes due to the increased donor ability of the nitrogen compared to the oxygen heteroatom. The formation of benzannulation products is favored, however, if the electron density at nitrogen is lowered by substitution with electron-withdrawing acyl groups [33]. The example in Scheme 12 demonstrates the effect. 

Although some C3 -A-debenzoyl A-acyl paclitaxels were evaluated, the impact of C3 -A substituents on antimmor activity seems to be somewhat complicated— neither electronic effects nor steric effects alone can be applied to explain the contributions of the acyl groups. 

In the reaction of benzofuroxan with unsymmetrical 1,3-diketoncs, or of unsymmetrically substituted benzofuroxan,however, two different isomeric products can be formed. Stehc and electronic effects influence the regioselectivity of this reaction and determine which group forms the acyl and which the quinoxaline substituent in the product. ... 

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