Conjugation energy

Conjugation Energies op Groups with the Cyanuric and Cyameluric Nuclei... 

In solution aliphatic and aromatic sulfines combine with aromatic and aliphatic thiones to yield 1,2,4-oxadithiolanes.169,170 Cycloadducts with only aromatic substituents could not be obtained, since the conjugation energy of aromatic sulfine drives the equilibrium to the reactant side.170 Thiobenzophe-none- and thiofluorenone-sulfines react with 3 to afford 1,2,4-trithiolanes.171 This is interpreted by assuming that 1,2,4-oxadithiolanes are formed in a first step, hence converted to 1,2,4-trithiolane. 

The description of conjugated dienes as shown by equation 17 and the associated comparison with butadiene in equation 18 corresponds most closely to the conventional definition. The results are plausible in that groups on one double bond that are c/5-situated relative to the other encourage nonplanarity, cause destabilization and result in lessened conjugation energy. Or so we say. The biggest debit of this approach is that the thermochemistry of the monoenes related by single addition of H2 is often absent. An example... 

Radialene 52 has been envisaged as a precursor to hexaethynyl[3]radialene, a potential building block for carbon networks. However, desilylation under very mild conditions led to an unstable product of so far unknown identity. In this context, it should be mentioned that according to thermochemical calculations, the still unknown hexaethynyl[3]radialene has an increased conjugation energy with respect to vinylacetylene, probably because of partial relief of strain in the radialene corc26b. A remarkable aspect of 52 is its color the crystals are deep-red and a hexane solution has a purple color. In this respect, 52 differs from the yellow radialenes 50 and 51 and resembles [3]radialenes such as 27 and 38, which have much more extended --systems. 

For all 3-substituted pyrroles the long-wavelength absorption is usually 15-20 nm lower than for the corresponding 2-derivatives, indicating that although the difference in conjugation energy in the... 

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