π* →nFluorescence Transition in Formaldehyde in Aqueous Solution:  A Combined Quantum Chemical Statistical Mechanical Study

2006 ◽  
Vol 110 (5) ◽  
pp. 1934-1942 ◽  
Author(s):  
Anders Öhrn ◽  
Gunnar Karlström
Keyword(s):  
Aqueous Solution ◽  
Quantum Chemical ◽  
Mechanical Study ◽  
Statistical Mechanical

C60(g), C70(g), saturated carbon vapour and increase of cluster populations with temperature: A combined AM1 quantum-chemical and statistical-mechanical study

1987 ◽  
Vol 52 (12) ◽  
pp. 2831-2838 ◽  
Author(s):  
Zdeněk Slanina ◽  
Jerzy M. Rudziński ◽  
Eiji Ōsawa
Keyword(s):  
Quantum Chemical ◽  
Equilibrium Constants ◽  
The Other ◽  
Am1 Method ◽  
Partition Functions ◽  
Saturated Vapour ◽  
Mechanical Study ◽  
Statistical Mechanical ◽  
Small Clusters ◽  
Chemical Description

Saturated vapour above graphite and the content of Cn(g) aggregates therein have been studied at various temperatures. The equilibrium constants of C(g) into Cn(g) association have been obtained for: (i) n = 1-5 from the available tabulated thermodynamical data, (ii) C60 and C70 from a quantum-chemical description in terms of the AM1 method as a source of molecular parameters for the construction of partition functions, and (iii) the other aggregates by linear inter- or extrapolation of the data sub (i) and (ii). The content of clusters with n ≥ 2 in the saturated vapour has been shown to increase steeply with temperature. This increase is due to small clusters (n ~ 2-5), whereas the recently proved particular structures C60 and C70 are - according to these calculations – negligibly populated in the saturated vapour at all temperatures studied. At the conditions of saturated vapour the population of C60 always exceeds that of C70 by several orders of magnitude. The relations of these calculations to the recent observations of distinct populations of C60 and C70 are discussed.

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.

Intermolecular Interactions of Pyridine in Liquid Phase and Aqueous Solution Studied by Soft X-ray Absorption Spectroscopy

2018 ◽  
Vol 232 (5-6) ◽  
pp. 705-722 ◽  
Author(s):  
Masanari Nagasaka ◽  
Hayato Yuzawa ◽  
Nobuhiro Kosugi
Keyword(s):  
Aqueous Solution ◽  
Quantum Chemical Calculations ◽  
Intermolecular Interactions ◽  
Absorption Spectroscopy ◽  
Quantum Chemical ◽  
Bulk Water ◽  
Pure Liquid ◽  
Rich Region ◽  
X Ray ◽  
X Ray Absorption

Abstract Intermolecular interactions of pyridine in liquid and in aqueous solution are studied by using soft X-ray absorption spectroscopy (XAS) at the C, N, and O K-edges. XAS of liquid pyridine shows that the N 1s→π* peak is blue shifted and the C 1s→π* peak of the meta and para sites is red shifted, respectively, as compared with XAS of pyridine gas. These shifts in liquid are smaller than those in clusters, indicating that the intermolecular interaction of liquid pyridine is weaker than that of pyridine cluster, as supported by the combination of quantum chemical calculations of the core excitation and molecular dynamics simulations of the liquid structure. On the other hand, XAS spectra of aqueous pyridine solutions (C5H5N)x(H2O)1−x measured at different molar fractions show that in the pyridine rich region, x>0.7, the C and N 1s→π* peak energies are not so different from pure liquid pyridine (x=1.0). In this region, antiparallel displaced structures of pyridine molecules are dominant as in pure pyridine liquid. In the O K-edge XAS, the pre-edge peaks sensitive to the hydrogen bond (HB) network of water molecules show the red shift of −0.15 eV from that of bulk water, indicating that small water clusters with no large-scale HB network are formed in the gap space of structured pyridine molecules. In the water rich region, 0.7>x, the N 1s→π* peaks and the O 1s pre-edge peaks are blue shifted, and the C 1s→π* peaks of the meta and para sites are red-shifted by increasing molar fraction of water. The HB network of bulk water is dominant, but quantum chemical calculations indicate that small pyridine clusters with the HB interaction between the H atom in water and the N atom in pyridine are still existent even in very dilute pyridine solutions.

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