Papers by Carlos R Cardenas
Journal of Physical Chemistry A, 2009
The second-order response of the electron density with respect to changes in electron number, kno... more The second-order response of the electron density with respect to changes in electron number, known as the dual descriptor, has been established as a key reactivity indicator for reactions like pericyclic reactions, where reagents accept and donate electrons concurrently. Here we establish that the dual descriptor is also the key reactivity indicator for ambiphilic reagents: reagents that can act either as electrophiles or as nucleophiles, depending on the reaction partner. Specifically, we study dual atoms (which are proposed to act, simultaneously, as an electron acceptor and an electron donor), dual molecules (which react with both electrophiles and nucleophiles, generally at different sites), and dual ion-molecule complexes (which react with both cations and anions). On the basis of our analysis, the dual atom (an Al(I) that has been purported to be dual in the literature) is actually pseudodual in the sense that it does not truly accept electrons from a nucleophiles; rather, it serves as a conduit through which an electrophile can donate electrons to the attached aromatic ring. For understanding dual ion-molecule complexes, it helps to understand that the dual descriptor makes a key contribution to the long-range portion of the quadratic hyperpolarization. In all cases, a complete description of the reactivity of the ambiphilic reagent requires considering both an orbital-based descriptor of electron transfer (the dual descriptor or the local hypersoftness) and the electrostatic potential. The local hypersoftness strongly resembles the dual descriptor.
International Journal of Quantum Chemistry, 2007
The Fukui function, hardness, and other reactivity indices defined in the context of the Kohn–Sha... more The Fukui function, hardness, and other reactivity indices defined in the context of the Kohn–Sham scheme have been further examined following up previous developments. An equation analogue to the Berkowitz–Parr relationship among the noninteracting linear response function and a new Kohn–Sham softness hierarchy can be derived as defined in the present study. The thermodynamic-like structure of the mathematical equations is retained among the global, local, and nonlocal hierarchies of descriptors, yielding equations that present fewer approximations. In particular, it is stressed that the Kohn–Sham hardness is better approximated by the Kohn–Sham energy gap and, as previously emphasized, that the Kohn–Sham Fukui function is precisely equal to the square of the frontier orbital. The higher-order perturbational extensions have been outlined, and the analogue of a Fukui response function within the Kohn–Sham context has been derived. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Journal of Physical Chemistry A, 2009
The second-order response of the electron density with respect to changes in electron number, kno... more The second-order response of the electron density with respect to changes in electron number, known as the dual descriptor, has been established as a key reactivity indicator for reactions like pericyclic reactions, where reagents accept and donate electrons concurrently. Here we establish that the dual descriptor is also the key reactivity indicator for ambiphilic reagents: reagents that can act either as electrophiles or as nucleophiles, depending on the reaction partner. Specifically, we study dual atoms (which are proposed to act, simultaneously, as an electron acceptor and an electron donor), dual molecules (which react with both electrophiles and nucleophiles, generally at different sites), and dual ion-molecule complexes (which react with both cations and anions). On the basis of our analysis, the dual atom (an Al(I) that has been purported to be dual in the literature) is actually pseudodual in the sense that it does not truly accept electrons from a nucleophiles; rather, it serves as a conduit through which an electrophile can donate electrons to the attached aromatic ring. For understanding dual ion-molecule complexes, it helps to understand that the dual descriptor makes a key contribution to the long-range portion of the quadratic hyperpolarization. In all cases, a complete description of the reactivity of the ambiphilic reagent requires considering both an orbital-based descriptor of electron transfer (the dual descriptor or the local hypersoftness) and the electrostatic potential. The local hypersoftness strongly resembles the dual descriptor.
International Journal of Quantum Chemistry, 2007
The Fukui function, hardness, and other reactivity indices defined in the context of the Kohn–Sha... more The Fukui function, hardness, and other reactivity indices defined in the context of the Kohn–Sham scheme have been further examined following up previous developments. An equation analogue to the Berkowitz–Parr relationship among the noninteracting linear response function and a new Kohn–Sham softness hierarchy can be derived as defined in the present study. The thermodynamic-like structure of the mathematical equations is retained among the global, local, and nonlocal hierarchies of descriptors, yielding equations that present fewer approximations. In particular, it is stressed that the Kohn–Sham hardness is better approximated by the Kohn–Sham energy gap and, as previously emphasized, that the Kohn–Sham Fukui function is precisely equal to the square of the frontier orbital. The higher-order perturbational extensions have been outlined, and the analogue of a Fukui response function within the Kohn–Sham context has been derived. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Se intenta en éste escrito una interpretación que demuestre que la actividad de concebir y la act... more Se intenta en éste escrito una interpretación que demuestre que la actividad de concebir y la actividad de diseñar en el proceso de proyecto no solo tienen características contrapuestas sino que además produce un enfrentamiento de dos deseos, una lucha de prestigio entre el Arquitecto (el que concibe) y el Diseñador (el que diseña).
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Papers by Carlos R Cardenas