Ab Initio Quantum Chemical Studies of the pKa's of Hydroxybenzoic Acids in Aqueous Solution with Special Reference to the Hydrophobicity of Hydroxybenzoates and Their Binding to Surfactants

1998 ◽  
Vol 102 (11) ◽  
pp. 1938-1944 ◽  
Author(s):  
Warwick A. Shapley ◽  
George B. Bacskay ◽  
Gregory G. Warr
Keyword(s):  
Aqueous Solution ◽  
Ab Initio ◽  
Special Reference ◽  
Quantum Chemical ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Hydroxybenzoic Acids

scholarly journals Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution

Symmetry ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 497
Author(s):  
Ewa D. Raczyńska
Keyword(s):  
Aqueous Solution ◽  
Quantum Chemical ◽  
Biologically Active ◽  
Deprotonation Reaction ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Scanty Information ◽  
Derivatives Of ◽  
Common Anion ◽  
Tautomeric Mixture

Keto-enol prototropic conversions for carbonyl compounds and phenols have been extensively studied, and many interesting review articles and even books appeared in the last 50 years. Quite a different situation takes place for derivatives of biologically active azulene, for which only scanty information on this phenomenon can be found in the literature. In this work, quantum-chemical studies have been undertaken for symmetrically and unsymmetrically substituted azulenols (constitutional isomers of naphthols). Stabilities of two enol (OH) rotamers and all possible keto (CH) tautomers have been analyzed in the gas phase {DFT(B3LYP)/6-311+G(d,p)} and also in aqueous solution {PCM(water)//DFT(B3LYP)/6-311+G(d,p)}. Contrary to naphthols, for which the keto forms can be neglected, at least one keto isomer (C1H, C2H, and/or C3H) contributes significantly to the tautomeric mixture of each azulenol to a higher degree in vacuo (non-polar environment) than in water (polar amphoteric solvent). The highest amounts of the CH forms have been found for 2- and 5-hydroxyazulenes, and the smallest ones for 1- and 6-hydroxy derivatives. The keto tautomer(s), together with the enol rotamers, can also participate in deprotonation reaction leading to a common anion and influence its acid-base properties. The strongest acidity in vacuo exhibits 6-hydroxyazulene, and the weakest one displays 1-hydroxyazulene, but all azulenols are stronger acids than phenol and naphthols. Bond length alternation in all DFT-optimized structures has been measured using the harmonic oscillator model of electron delocalization (HOMED) index. Generally, the HOMED values decrease for the keto tautomers, particularly for the ring containing the labile proton. Even for the keto tautomers possessing energetic parameters close to those of the enol isomers, the HOMED indices are low. However, some kind of parallelism exists for the keto forms between their relative energies and HOMEDs estimated for the entire molecules.

Cluster Models for Calcite Surfaces:  Ab Initio Quantum Chemical Studies

1999 ◽  
Vol 103 (32) ◽  
pp. 6734-6740 ◽  
Author(s):  
Henna Ruuska ◽  
Pipsa Hirva ◽  
Tapani A. Pakkanen
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Cluster Models ◽  
Chemical Studies ◽  
Quantum Chemical Studies
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