On the rotational isomerism of one rotor molecules. A comparative study of the HSSH and HXNX (X = O,S) series of molecules

Cárdenas-Jirón, Gloria I.; Cárdenas-Lailhacar, Cristián; Toro–Labbé, Alejandro

doi:10.1016/0166-1280(90)80053-q

Cited by 20 publications

(8 citation statements)

References 13 publications

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“…The parameter β is known as the Brønsted coefficient, and physically it represents a measure of the degree of resemblance of the transition state with respect to the product. The Brønsted coefficient is often used to quantify the empirical concepts of reactant-like (0 ≤ β ≤ 1 / 2 ) and product-like ( 1 / 2 ≤ β ≤ 1) transition state. ,,− By evaluating eq 9 in ω = β we obtain an alternative expression for the activation energy, now in terms of the activation chemical potential (Δμ ⧧ ≡ μ(β)) and the activation hardness (Δη ⧧ ≡ η(β)): This equation connecting the three activation properties might provide new interpretations of the nature of activation energies, and certainly it may help to give new insights about reaction mechanisms. It has been found in different types of reactions that μ and η pass through an extrema at β or very near to it; − this ensures that eq 19 produces reliable values of potential barriers from the knowledge of activation electronic properties.…”

Section: Theorymentioning

confidence: 99%

“… , In the case of the inversion mechanism, calculations at ω = 0 and ω = 0.0105 (θ = 0° and 10°, respectively) led to k t , μ t , and η t , and calculations at ω = 0.9715 and ω = 1 (θ = 129.29° and 139.29°, respectively) led to k c , μ c and η c . For a more detailed discussion about the procedure we use to numerically obtain the input parameters needed to define V (ω), μ(ω) and η(ω), the reader is referred to our previous papers. − In Table are quoted the input parameters necessary to obtain the profiles of these properties along the reaction paths.…”

Section: Calculationsmentioning

confidence: 99%

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Relations between Potential Energy, Electronic Chemical Potential, and Hardness Profiles

et al. 1997

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In recent papers we defined a theoretical frame aimed at characterizing the hardness and potential energy profiles along a reduced reaction coordinate (ω) varying from 0 to 1. In this paper we generalize that model to propose a global procedure that allows one to consider simultaneously the evolution of the potential energy (V) in connection with that of the electronic chemical potential (μ) and the molecular hardness (η). Important results have been obtained: (a) the potential energy profile can be expressed in terms of the μ and η profiles through an equation which is analogous to that used by Parr and Pearson to demonstrate the HSAB principle; (b) the chemical potential along ω is in turn written in terms of the hardness profile, an equation which is analogous to that proposed by the same authors to quantify the electron tranfer induced by a chemical potential gradient; and (c) useful expressions for the activation properties have been derived. As an illustration we study the trans ⇌ cis isomerization of diimide, a reaction that may occur through either an internal rotation or an inversion mechanism. The most relevant result concerning the chemical system is that for both mechanisms the principle of maximum hardness holds even though the electronic chemical potential strongly varies along the reaction coordinates. Our analysis suggests that if a system is constrained to chose among different reaction paths connecting two stable states, it will prefer the one presenting a minimum chemical potential.

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Section: Theorymentioning

confidence: 99%

Section: Calculationsmentioning

confidence: 99%

Relations between Potential Energy, Electronic Chemical Potential, and Hardness Profiles

et al. 1997

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“…trans-isomer, although the former has less stability than the latter (Cárdenas-Jirón et al 1990). The lower stability of the cisisomer is a more prominent steric effect, because their hydrogens are partially eclipsed.…”

Section: Irradiation Of Pure H 2 S Ice Experimentsmentioning

confidence: 99%

Sulfur depletion in dense clouds and circumstellar regions

Jiménez-Escobar

Muñoz

2011

A&A

121

106

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Aims. This work aims to study the unexplained sulfur depletion observed toward dense clouds and protostars. Methods. We made simulation experiments of the UV-photoprocessing and sublimation of H 2 S and H 2 S:H 2 O ice in dense clouds and circumstellar regions, using the InterStellar Astrochemistry Chamber (ISAC), a state-of-the-art ultra-high-vacuum setup. The ice was monitored in situ by mid-infrared spectroscopy in transmittance. Temperature-programmed desorption (TPD) of the ice was performed using a quadrupole mass spectrometer (QMS) to detect the volatiles desorbing from the ice.Results. Comparing our laboratory data to infrared observations of protostars we obtained a more accurate upper limit of the abundance of H 2 S ice toward these objects. We determined the desorption temperature of H 2 S ice, which depends on the initial H 2 S:H 2 O ratio. UV-photoprocessing of H 2 S:H 2 O ice led to the formation of several species. Among them, H 2 S 2 was found to photodissociate forming S 2 and, by elongation, other species up to S 8 , which are refractory at room temperature. A large fraction of the missing sulfur in dense clouds and circumstellar regions could thus be polymeric sulfur residing in dust grains.

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“…At this point it should be emphasized that eq 11 may present numerical instabilities in cases where ß or ß' is very close to xh. However, eq 11 presents additional qualitative and methodological interests. It allows one to derive rules for hardness and energy that relate the maximum hardness principle with the Hammond postulate, as we shall see below.…”

Section: Theorymentioning

confidence: 99%

Hardness Profile and Activation Hardness for Rotational Isomerization Processes. 2. The Maximum Hardness Principle

Cárdenas-Jirón¹,

Toro–Labbé²

1995

J. Phys. Chem.

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In a recent paper [/. Phys. Chem. 1995, 99, 5325] we presented a model characterizing the activation hardness in terms of the activation energy of rotational isomerization reactions. We present in this paper an extension of that model for obtaining a direct relation between hardness and potential energy profiles. The hardness is related to the potential energy through a two-term equation in which the leading term is a linear dependence on the potential energy, and the second term can be seen as a correction occurring in cases where the critical points for hardness and energy profiles do not match. It is shown that the hardness and energy profiles behave in opposite ways that can be rationalized in terms of two parameters. A qualitative proof of the maximum hardness principle (PMH), within the frame of the model potential employed, is given, and its consistency with the Hammond postulate is discussed in the light of results for different molecules presenting rotational isomerization.

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On the rotational isomerism of one rotor molecules. A comparative study of the HSSH and HXNX (X = O,S) series of molecules

Cited by 20 publications

References 13 publications

Relations between Potential Energy, Electronic Chemical Potential, and Hardness Profiles

Relations between Potential Energy, Electronic Chemical Potential, and Hardness Profiles

Sulfur depletion in dense clouds and circumstellar regions

Hardness Profile and Activation Hardness for Rotational Isomerization Processes. 2. The Maximum Hardness Principle

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