Investigation on Intramolecular Hydrogen Bond and Some Thermodynamic Properties of Polyhydroxylated Anthraquinones

Anthraquinone and polyhydroxylated anthroquinones (PHOAQs) have been studied at the B3LYP/6-311G** level using the Gaussian 09 program. The isodesmic reactions were designed to calculate the standard enthalpy of formation (ΔfHθ) and standard Gibbs energy of formation (ΔfGθ) for PHOAQ congeners. Two kinds of intramolecular hydrogen bonds exist in PHOAQs, and the isodesmic reactions of isomerization were used to determine the intramolecular hydrogen bond energy. The Atoms in Molecules (AIM) 2000 program (version 1.0) was used to study the characteristics of the hydrogen bonds. Relations of Sθ, ΔfHθ, and ΔfGθ with the number and position of hydroxyl substitution (NPHOS) were also discussed. How the intramolecular hydrogen bond influences ionization was investigated, and the first-order ionization constant for the most likely ionization path of the most stable conformations in each group of isomers was obtained with the self-consistent reaction field (SCRF) method.