Conjugating ability

Contrary to fraras-azoferrocene, the cis form exhibits one-step 2e oxidation waves, and its oxidation potential, E° = 0.03 V in Bu4NC104-benzonitrile, is more negative than that of the trans form (E() = 0.29 and 0.50 V vs. Ag/Ag ) by 0.3 V. These data imply that the 7r-conjugation ability and electron-withdrawing nature of the azo group is retarded in the cis form. 

While the jr-conjugation ability of phosphorus compounds does not seem to depend on the size of... 

C. The smaller retarding effect of the thioxo group when introduced into the more flexible system supports the applicability of the authors methodology to change the conjugative ability of bridgehead carbocations. 

In dianion-diradicals, two vacant orbitals are populated, that is, LUMO and the next (somewhat higher) nnoccupied one. This next orbital must, nevertheless, be situated low enough. Such an orbital can be detected in molecules of unsaturated hydrocarbons of a widespread contour. Within this expanded contour, extensible electron delocalization somewhat decreases the repulsion energy. Several electron-acceptor fragments (substituents with heteroatoms or with high conjugation ability) assist in the formation of poly(anion-radicals). 

With some of the phase 2 metabolizing enzymes, there may be strict ontogenetic patterns of expression. Sulfate conjugation ability occurs early in rats, whereas glucuronidation (of xenobiotics), and conjugation with glutathione and amino acids, only develop over about 30 days from birth. 

Apart from thioacetals, allyl sulfides are among the easiest sulfides to deprotonate and alkylate because of the conjugating ability of the allyl group. However, the very delocalization that assists anion formation means that the anions often react unregioselectively lithiated phenyl allyl sulfide, for instance, reacts with hexyl iodide to give a 3 1 ratio of regioisomers. 

In the base-catalysed equilibration of 191 and 192 (equation 19) one observes301 a contest between the conjugative ability of a phenyl ring and a N-methylanilino group. The equilibrium lies again on the side of the enamine 192 to the extent of AG = —2.3(3) kcal mol-1 determined for the dimethylamino group302. 

Electronic excitation of cyclopropyl derivatives is discussed in detail in other chapters of this volume but because of the importance of some of these studies for the elucidation of the conjugative abilities of this group some mention of this topic here is warranted. 

If our interpretation of the g data in Tables I and III is correct, this suggests a direction for future research. Thus, if one wants to gain insight into the conjugating ability of three-membered rings, a study of the first a resonance in substituted cyclopropanes may prove unrewarding, but a study of the corresponding reso-... 

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