Hydrogen-bonded conjugates

Associates (donor-acceptor complexes or salts, self-aggregates and hydrogen-bonded conjugates)... 

Returning to the hydrogen-bonded conjugates according to Kolthoff and Chantooni49, we can mention the following examples of homoconjugate ions. 

In view of the hydrogen bond conjugation effect reported by Lemieux and Pavia (17), the gradual addition of dimethyl sulfoxide to a solution of 4 in 1,2-dichloroethane should initially enrich the population... 

Both enols have their carbon-carbon double bonds conjugated to a carbonyl group and can form an intramolecular hydrogen bond They are of comparable stability... 

Conjugation is more important 1 3 Cyclohexanedione exists mainly in its enol form in spite of the fact that intramolecular hydrogen bonding is impossible due to the distance between the carbonyl group and the enohc —OH group... 

Peroxyesters, particularly those with a-hydrogens or conjugated double bonds, are susceptible to iaduced decomposition under certain conditions, but they are generally less susceptible than diacyl peroxides. Lower molecular weight peroxyesters that have some water solubiUty can be hydroly2ed. 

A significant modification in the stereochemistry is observed when the double bond is conjugated with a group that can stabilize a carbocation intermediate. Most of the specific cases involve an aryl substituent. Examples of alkenes that give primarily syn addition are Z- and -l-phenylpropene, Z- and - -<-butylstyrene, l-phenyl-4-/-butylcyclohex-ene, and indene. The mechanism proposed for these additions features an ion pair as the key intermediate. Because of the greater stability of the carbocations in these molecules, concerted attack by halide ion is not required for complete carbon-hydrogen bond formation. If the ion pair formed by alkene protonation collapses to product faster than reorientation takes place, the result will be syn addition, since the proton and halide ion are initially on the same side of the molecule. 

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