title: Hypervalency in Organic Crystals: A Case Study of the Oxicam Sulfonamide Group.
abstract: The theoretical charge density of the active pharmaceutical ingredient piroxicam (PXM) was evaluated through density functional theory with a localized basis set. To understand the electronic nature of the sulfur atom within the sulfonamide group, a highly ubiquitous functional group in pharmaceutical molecules, a theoretical charge density study was performed on PXM within the framework of Bader theory. Focus is on developing a topological description of the sulfur atom and its bonds within the sulfonamide group. It was found that sulfur d-orbitals do not participate in bonding. Instead, the existence of a strongly polarized ("ionic") bonding structure is found through a combined topological and natural bonding orbital analysis. This finding is in stark contrast to long-held theories of the bonding structure of organic sulfonamide and has important implications for the parametrization of calculations using classical approaches.
authors.affiliation: Novosibirsk State University , Pirogova 2, Novosibirsk 630090, Russian Federation.|Institute of Solid State Chemistry and Mechanochemistry SB RAS , Kutateladze 18, Novosibirsk 630128, Russian Federation.
authors.forename: Christian
authors.identifier: http://orcid.org/0000-0002-2412-9859
authors.initials: C
authors.lastname: Tantardini
authors.affiliation: Novosibirsk State University , Pirogova 2, Novosibirsk 630090, Russian Federation.|Institute of Solid State Chemistry and Mechanochemistry SB RAS , Kutateladze 18, Novosibirsk 630128, Russian Federation.
authors.forename: Elena V
authors.initials: EV
authors.lastname: Boldyreva
authors.affiliation: Novosibirsk State University , Pirogova 2, Novosibirsk 630090, Russian Federation.|Scuola Superiore Normale , Piazza dei Cavalieri 7, Pisa 56126, Italy.
authors.forename: Enrico
authors.identifier: http://orcid.org/0000-0002-4614-1568
authors.initials: E
authors.lastname: Benassi
mesh_terms: D008968:Molecular Conformation; D010894:Piroxicam / Q000737:chemistry*; D011789:Quantum Theory; D000077145:Sulfanilamide; D013424:Sulfanilamides / Q000737:chemistry*
chemical_list: D013424:Sulfanilamides; D010894:Piroxicam; D000077145:Sulfanilamide