In the present paper we address the problem of optical isomerism embodied in the socalled “Hund’s paradox”, which points to the difficulty to account for chirality by means of quantum mechanics. In particular, we explain the answer to the problem proposed by the theory of decoherence. The purpose of this article is to challenge this answer on the basis of a conceptual analysis of the phenomenon of decoherence, that reveals the limitations of the theory of decoherence to solve the difficulties (...) posed by optical isomerism and, in general, by quantum measurement. (shrink)

Perhaps the hottest topic in the philosophy of chemistry is that of the relationship between chemistry and physics. The problem finds one of its main manifestations in the debate about the nature of molecular structure, given by the spatial arrangement of the nuclei in a molecule. The traditional strategy to address the problem is to consider chemical cases that challenge the definition of molecular structure in quantum–mechanical terms. Instead of taking that top-down strategy, in this paper we face the problem (...) of the reduction of molecular structure to quantum mechanics from a bottom-up perspective: our aim is to show how the theoretical peculiarities of quantum mechanics stand against the possibility of molecular structure, defined in terms of the spatial relations of the nuclei conceived as individual localized objects. We will argue that, according to the theory, quantum “particles” are not individuals that can be identified as different from others and that can be reidentified through time; therefore, they do not have the ontological stability necessary to maintain the relations that can lead to a spatially definite system with an identifiable shape. On the other hand, although quantum chemists use the resources supplied by quantum mechanics with successful results, this does no mean reduction: their “approximations” add certain assumptions that are not justified in the context of quantum mechanics or are even inconsistent with the very formal structure of the theory. (shrink)

According to classical molecular chemistry, molecules have a structure, that is, they are sets of atoms with a definite arrangements in space and held together by chemical bonds. The concept of molecular structure is central to modern chemical thought given its impressive predictive power. It is also a very useful concept in chemistry education, due to its role in the rationalization and visualization of microscopic phenomena. However, such a concept seems to find no place in the ontology described by quantum (...) mechanics, since it appeals to classical notions such as the position of the atomic nuclei or the individuality of electrons. Although this problem has attracted the attention of several authors, the discussion is far from settled. Some authors adopt an explicitly reductionist position and advocate to reconstruct the concept of molecular structure within the framework of the quantum theory. Others, although acknowledging the conceptual discontinuity between quantum mechanics and molecular chemistry, keep the hope of future reduction alive. From an explicitly non-reductionist position, on the contrary, others authors conceive molecular structure as an emergent phenomenon. The purpose of this article is to propose a different line of argumentation to address this problem. By contrast to reduction and emergence, the admission of a multiplicity of ontologies, not necessarily linked by hierarchical connections, cancels the need of finding a relation of dependence between the molecular level and the quantum level. This ontologically pluralist position can be applied to the issue of molecular structure, in order to argue that it is possible to admit the existence of structure in the ontology of molecular chemistry, in spite of the fact that it does not exist in the quantum world. (shrink)

In a recent article entitled “The problem of molecular structure just is the measurement problem”, Alexander Franklin and Vanessa Seifert argue that insofar as the quantum measurement problem is solved, the problems of molecular structure are resolved as well. The purpose of the present article is to show that such a claim is too optimistic. Although the solution of the quantum measurement problem is relevant to how the problem of molecular structure is faced, such a solution is not sufficient to (...) account for the structure of molecules as understood in the field of chemistry. (shrink)

In the present paper we address the problem of optical isomerism embodied in the socalled “Hund’s paradox”, which points to the difficulty to account for chirality by means of quantum mechanics. In particular, we explain the answer to the problem proposed by the theory of decoherence. The purpose of this article is to challenge this answer on the basis of a conceptual analysis of the phenomenon of decoherence, that reveals the limitations of the theory of decoherence to solve the difficulties (...) posed by optical isomerism and, in general, by quantum measurement. (shrink)

The modal-Hamiltonian interpretation belongs to the modal family of interpretations of quantum mechanics. By endowing the Hamiltonian with the role of selecting the subset of the definite-valued observables of the system, it accounts for ideal and non-ideal measurements, and also supplies a criterion to distinguish between reliable and non-reliable measurements in the non-ideal case. It can be reformulated in an explicitly invariant form, in terms of the Casimir operators of the Galilean group, and the compatibility of the MHI with the (...) theory of decoherence has been proved. Nevertheless, perhaps its main advantage in the eyes of a scientist is given by its several applications to well-known physical situations, leading to results compatible with experimental evidence. The purpose of this paper is to add a new application to the list: the case of optical isomerism, which is a central issue for the philosophy of physics and of chemistry since it points to the core of the problem of the relationship between physics and chemistry. Here it will be shown that the MHI supplies a direct and physically natural solution to the problem, a solution that does not require putting classical assumptions in “by hand.”. (shrink)

Intra-molecular connectivity (that is, chemical structure) does not emerge from computations based on fundamental quantum-mechanical principles. In order to compute molecular electronic energies (of C 3 H 4 hydrocarbons, for instance) quantum chemists must insert intra-molecular connectivity “by hand.” Some take this as an indication that chemistry cannot be reduced to physics: others consider it as evidence that quantum chemistry needs new logical foundations. Such discussions are generally synchronic rather than diachronic —that is, they neglect ‘historical’ aspects. However, systems of (...) interest to chemists generally are metastable . In many cases chemical systems of a given elemental composition may exist in any one of several different metastable states depending on the history of the system. Molecular structure generally depends on contingent historical circumstances of synthesis and separation, rather than solely or mainly on relative energies of alternative stable states, those energies in turn determined by relationships among components. Chemical structure is usually ‘kinetically-determined’ rather than ‘thermodynamically-determined.’ For instance, cyclical hydrocarbon ring-systems (as in cyclopropene) are produced only in special circumstances. Adequate theoretical treatments must take account of the persistent effects of such contingent historical events whenever they are relevant—as they generally are in chemistry. (shrink)