On violations of Le Chatelier's principle for a temperature change in small systems observed for short times

Le Chatelier's principle states that when a system is disturbed, it will shift its equilibrium to counteract the disturbance. However for a chemical reaction in a small, confined system, the probability of observing it proceed in the opposite direction to that predicted by Le Chatelier's principle, can be significant. This work gives a molecular level proof of Le Chatelier's principle for the case of a temperature change. Moreover, a new, exact mathematical expression is derived that is valid for arbitrary system sizes and gives the relative probability that a single experiment will proceed in the endothermic or exothermic direction, in terms of a microscopic phase function. We show that the average of the time integral of this function is the maximum possible value of the purely irreversible entropy production for the thermal relaxation process. Our result is tested against computer simulations of the unfolding of a polypeptide. We prove that any equilibrium reaction mixture on average responds to a temperature increase by shifting its point of equilibrium in the endothermic direction

Molecular structure, spectroscopic investigations and computational study on the potential molecular switch of (<i>E</i>)-1-(4-(2-hydroxybenzylideneamino)phenyl)ethanone

<p>This paper presents a combined experimental and theoretical study on an ortho-hydroxy Schiff base compound, (<i>E</i>)-1-(4-(2-hydroxybenzylideneamino)phenyl)ethanone. The spectroscopic and electrochemical properties of the compound were determined using IR, UV–vis and ¹H, ¹³C NMR as well as cyclic voltammetry techniques. The hydrogen bond strength was studied using the spectroscopic results, geometry calculations, topological and NBO analysis. The results showed that the predicted nonlinear optical (NLO) properties of the title compound are much greater than those of urea. Thermodynamic properties in the range from 100 to 505 K were obtained. Furthermore, molecular electrostatic potential, Fukui functions, thermodynamic, frontier molecular orbital analysis, reactivity descriptors and NLO properties were found and discussed. Theoretical results show that the conductance of the two tautomers varies seriously, which offers that this molecule has potential usage as a molecular device.</p> <p></p