Similarity laws in thermodynamics: Monomers and dimers and their relations to crises in society

In the present paper, we consider unexplained experiments known for centuries, which appear in reference books and were obtained both by physicists-experimenters and with the help of a mathematical experiment.     

Intermolecular Hydrogen Bonding and Proton Transfer in the Ground and Lowest Excited Singlet States of the Ethyl Esters of 1- and 2-naphthoic Acid

The absorption spectra of ethyl 1-naphthoate in hexane and in water demonstrate normal dependences upon solvent hydrogen bonding and polarity properties while the absorption spectra of 1-naphthoic acid do not. This is attributed to inhibition of conjugation by steric interference between the carbethoxy group of the ester or the hydrated carboxyl group of the acid and the peri-hydrogen atom of the naphthalene ring in the 5-position, in the ground electronic state. The anomalous fluorimetric titration characteristics of the 1- and 2- naphthoic esters and of 1-naphthoic acid are attributed to hydrogen bonded exciplex formation in the lowest excited singlet state.

In a recent study of the solvent and acidity dependences of the electronic absorption and fluorescence spectra of 1- and 2-naphthoic acid (1) several phenomena were observed which were rather unusual and whose explanations were beyond the scope of the previous study. Among these were 1) the red shift of the absorption spectra upon going from water to hexane media and 2) the destruction of the conjugate relationship between the excited acidium cations and neutral molecules of the 1-isomer as evidenced by the fluorimetric titrations of these species occurring in different pH regions In order to more closely examine these phenomena and perhaps to explain them in terms of the interactions of the protonated and neutral car box y groups with the solvent and the naphthalene ring, the present study of the lectronic absorption and fluorescence spectra of the ethyl esters of 1- and 2-naphthoic acid was undertaken.     

The energetics of naphthalene derivatives,III: phenylacetic acid and the isomeric 1- and 2-naphthylacetic acids

Phenylacetic acid and the isomeric 1- and 2-naphthylacetic acids are at the confluence of diverse concepts, techniques and classes of organic compounds. Summing the results of our new enthalpy of formation of the gaseous phenylacetic acid reported herein, and of literature enthalpy of formation of the isomeric solid naphthylacetic acids and of our new sublimation enthalpies reported herein, we derive gas phase enthalpies of formation of ?314.7±3.1, ?246.9±2.0 and ?247.4±2.1kJmol^?1 respectively. This corresponds to 1- and 2-naphthylacetic acid having indistinguishable enthalpies of formation. We also performed MP2(full)/6-31G(d) calculations on these species, resulting in enthalpies of formation of ?307.3±0.8, ?247.4±3.4 and ?247.5±3.4kJmol^?1 for phenylacetic acid and 1- and 2-naphthylacetic acid in satisfactory agreement with the above experimental results.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1/2-1/2-1-1 and 3/2-3/2 -1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of1/2-1/2-1-1and 3/2-3/2-1-1are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it has two phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain, the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameterα=J2/J1.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1／2-1／2-1-1 and 3／2-3／2-1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of 1/2-1/2-1-1 and 3/2-3/2-1-1 are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it hastwo phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain,the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameter α=J2/J1.     

Near-infrared spectra of hydrogen-bonded cyclic dimers of some carboxylic acids

Near-infrared spectra in the 3900–11000 cm⁻¹ region were measured for formic and acetic acids and also for their deutero analogs in the gaseous state at various temperatures. Observed monomer and dimer bands were assigned to overtone and summation bands of various vibrational modes. Special attention was paid to the first overtone bands of the OH and OD stretching modes of the hydrogen-bonded cyclic dimers, which were observed at ∼5930 cm⁻¹ and ∼5870 cm⁻¹ for formic-d acid and acetic-d₃ acid, respectively, and also at ∼4370 cm⁻¹ for acetic acid-d. On the basis of these data the anharmonicity constants were calculated for the OH and OD stretching modes and were found to increase by hydrogen-bond formation in the gaseous state. Hydrogen-bonded overtone bands are broad and have submaxima with intervals nearly half of those of the OH and OD fundamental bands. The results concerning the band breadths of the OH and OD stretching vibrations of the dimers were interpreted on the line of the idea that they strongly couple with the O?O stretching vibration.     

Photoelectron spectroscopic studies of the monomers and dimers of acetic and trifluoracetic acids

Comparison of the He(I) and He(II) photoelectron spectra of acetic and trifluoracetic acids has clarified the assignments of their p-based ionization potentials. The He(I) spectra of the gas-phase homodimer of each molecule have been observed using a high-pressure nozzle inlet system operating at room temperature. Spectrum-stripping of the monomer—dimer mixed-spectra gives dimer spectra which are interpreted with the aid of molecular orbital calculations. Appropriate mixtures of the two acids have been analyzed to obtain the He(I) spectrum of the 1:1 heterodimer. Assignments of the three dimer spectra indicate that the inductive influences of the methyl and trifluoromethyl groups are transmitted across the hydrogen-bond bridges.     

Reactive scattering of alkali dimers: K2 + HgCl2, HgBr2, HgI2

Angular distribution measurements of KX reactive scattering of a potassium dimer K₂ beam by mercuric halide molecules HgX₂ are reported. All the reactions exhibit strong forward peaking in the centre of mass differential cross sections and large total reaction cross sections Q_r ～ 150 Ų. However, there is substantial backward peaking ( forward peak) for HgBr₂, HgI₂. Despite the direct stripping dynamics, both alkali atoms of the K₂ dimer become bound alkali halide molecules in most (perhaps all) reactive collisions. A major fraction of the reaction exoergicity is disposed into vibrational excitation of the product KX molecules. A mechanism involving a first electron jump in the entrance valley and a second electron jump in the exit valley of the potential surface is suggested to explain the rapid transfer of both K₂ valence electrons.     

Effect of phenols and carboxylic acids on photochromism of 1-alkyl-2-(arylazo)imidazoles

Light irradiated trans-to-cis isomerization of 1-alkyl-2-(arylazo)imidazole in the presence of phenol, catechol, benzoic acid and salicylic acid (called co-factors) has been studied in this work. The rate of trans→cis photoisomerization is decreased in the presence of co-factor in the medium and is dependent on the concentration of active quotient about photochrome. The decrease in rate follows catechol>benzoic acid>phenol>salicylic acid. This trend is due to the effects of dissociation ability of –O–H/–COOH, intermolecular association of the molecules etc. The reverse change, cis-to-trans, is very slow in light irradiation and has been carried out by a thermal process in the dark. The quantum yield of isomerization follows the same sequence of effects of co-factors.     

Reactive scattering of alkali dimers K2 + I2, CH2I2, CHI3, CBr4

Angular distribution measurements of KX reactive scattering of a potassium dimer K₂ beam by I₂ and by a series of halomethane molecules are reported. The K₂ + I₂ reactive scattering is similar to that previously observed for K₂ + Br₂. The predominant reaction path yields K + KI + I with the K and KI product recoiling in the forward direction. However, the forward peak of the KI differential cross section is lower than that for K from K₂ + I₂ and is broader than that observed for KBr from K₂ + Br₂. This is attributed to slow dissociation of the I ₂ ^- ion formed in the electron jump mechanism previously proposed for K₂ + Br₂. In the halomethane reactions, both alkali atoms of the K₂ dimer become bound alkali halide molecules in all reactive collisions, despite the direct dynamics of the corresponding supersonic K atom reactions. Thus, these reactions provide compelling evidence for a second electron jump mechanism, previously proposed for the reactions of K₂ dimers with polyhalide molecules. The differential cross sections for the K₂ dimer plus halomethane reactions indicate an osculating collision complex with a lifetime at least comparable to its rotational period, perhaps much longer. This reaction complex is identified with the doubly ionic state formed by the second electron jump transition.     

Mössbauer study of tin-doped 1-2-3 and 2-1-4 highT c superconductors

Samples of YBa₂(Cu_0.85Sn_0.15)₃O_7–y (1-2-3), La₂(Cu_0.95Sn_0.05)O4_4–x, and La_1.85Ba_0.15(Cu_0.95Sn_0.05)O_4–x (2-1-4), with different oxygen stoichiometry, have been studied by Mössbauer spectroscopy. These measurements reveal the existence of two inequivalent sites for Sn in the (1-2-3) compounds. The (1-2-3) spectra display two quadrupole doublets which we associate with Sn in Cu(1) and Cu(2) sites, respectively. La compounds show a single quadrupole doublet.     

Novel and convenient synthesis of 1-(pyridinylmethyl)-2-naphthols and 1-(pyridinylmethylene)-2-tetralones from 2-tetralones

The reaction of 2/4-pyridine carboxaldehyes with 2-tetralone analogs in the presence of catalytic amounts of Pd/C and trimethylsilyl chloride in DMF resulted in the formation of 1-(pyridin-2/4-ylmethyl)-2-naphthols in moderate to good yields as opposed to the expected 1-(pyridin-2/4-ylmethylene)-2-tetralones. 3-Pyridine carboxaldehyde, however, formed 1-(pyridin-3-ylmethylene)-2-tetralones with 2-tetralone analogs under similar conditions. When representative reactions were repeated in the presence of anhydrous HCl gas in acetic acid, including one with 3-pyridine carboxaldehyde, 1-(pyridinylmethyl)-2-naphthols were the only products obtained with significantly improved yields. A possible mechanism explaining these results is discussed.     

The magnetic phase in 2-2-1-2 superconducting materials

Three related aspects of the magnetic phase diagram are presented here: the first deals with the disruption of the antiferromagnetic order in the electron rich phase obtained by Ce doping, the second concern the role of Bi planes as a sink-buffer of carriers, the third focuses the magnetization vs. temperature curves in a variety of different bilayer materials as seen by the muons and discusses the “anomalous” behaviour in relation to theoretical predictions and neutron scattering data.     

Identification ofμ +-sites in the 1-2-3 compoundin the 1-2-3 compound

Possibleμ ⁺ sites have been identified by a comparison of measured spontaneous internal fields in YBa₂Cu₃O_6+δ and REBa₂Cu₃O_7−δ and of measured second moments and width of transverse field powder spectra with the corresponding calculated quantities. In the YBa₂Cu₃O₇ system only one possibleμ ⁺ site emerges at a distance of ∼1.05 A from a chain oxygen O(4) at the position (0.15(1), 0.44(1), 0.071(1)). In the system YBa₂Cu₃O₆ the only possibleμ ⁺ sites are near to an oxygen O(1) with z/c=0.133 and the same distance as above. The analysis leads also to improved valuesμ _Ho = 2.2(1)μ _B andμ _Cu = 0.67(4)μ _B and to a determination of the latters direction:μ _Cu ‖〈110〉.     

Features of dual fluorescence of 1, 2, 3, 4- tetrahydroisoquinoline

In polar and nonpolar solvents, tetrahydroisoquinoline emits S₂ (ππ¹) → S₀ and S₁ (ππ¹) → S₀ dual fluorescence and T₁ (ππ¹) → S₀ phosphorescence on S₂ (ππ¹) ← S₀ excitation. When excited by S₁ (ππ¹) ← S₀ the molecule yields S₁ (ππ¹) → S₀ fluorescence and T₁ (ππ¹) → S₀ phosphorescence in nonpolar solvent but only fluorescence in polar solvents. Probable participation of intermediate S₁ (nπ¹), T₁(nπ¹) states in intersystem crossing and internal conversion processes and its significance in interpreting the results are discussed.