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Semiempirical study of isomerism and intramolecular hydrogen bonds in some substituted anthraquinones

Structural properties and intramolecular hydrogen bonding in several isomers of dihydroxyanthraquinone were investigated by the semiempirical AM1 method. It is shown that the molecule involving two O-H groups attached at sites 9 and 10 is the least stable. The reason behind this finding is the underlying naphthalene fragment. The remaining three isomers are more stable and possess comparable heats of formation. Their higher stability is a consequence of the two peripheral almost benzene-like six-membered rings. It is found that all intramolecular hydrogen bonds are asymmetric. Theoretical estimates of their strength is favourably compared with available empirical data.

semiempirical calculations ; AM1 ; intramolecular hydrogen bonding

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