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1. Competition Between the Two σ‐Holes in the Formation of a Chalcogen Bond

   https://doi.org/10.1002/cphc.202200936  

   Scheiner, Steve (February 2023, ChemPhysChem)

   Abstract A chalcogen atom Y contains two separate σ‐holes when in a R₁YR₂molecular bonding pattern. Quantum chemical calculations consider competition between these two σ‐holes to engage in a chalcogen bond (ChB) with a NH₃base. R groups considered include F, Br, I, and tert‐butyl (tBu). Also examined is the situation where the Y lies within a chalcogenazole ring, where its neighbors are C and N. Both electron‐withdrawing substituents R₁and R₂act cooperatively to deepen the two σ‐holes, but the deeper of the two holes consistently lies opposite to the more electron‐withdrawing group, and is also favored to form a stronger ChB. The formation of two simultaneous ChBs in a triad requires the Y atom to act as double electron acceptor, and so anti‐cooperativity weakens each bond relative to the simple dyad. This effect is such that some of the shallower σ‐holes are unable to form a ChB at all when a base occupies the other site. 

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2. Participation of S and Se in hydrogen and chalcogen bonds

   https://doi.org/10.1039/D1CE01046H  

   Scheiner, Steve (October 2021, CrystEngComm)

   This article reviews the history and the current state of knowledge concerning the ability of the heavy chalcogen atoms S and Se, and to some extent Te, to participate in a H-bond as either proton donor or acceptor. These atoms are nearly as effective proton acceptors as O, and only slightly weaker as donor. They can also participate in chalcogen bonds where they act as electron acceptors from a nucleophile. These bonds rapidly strengthen as the chalcogen atom becomes larger: S < Se < Te, or if they are surrounded by electron-withdrawing substituents, and can exceed that of many types of H-bonds. Experimental and computational evidence indicates that both H-bonds and chalcogen bonds involving S and Se occur widely in chemical and biological systems, and play an active role in structure and function. 

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3. Cis/Trans Energetics in Epoxide, Thiirane, Aziridine and Phosphirane Containing Cyclopentanols: Effects of Intramolecular OH⋯O, S, N and P Contacts

   https://doi.org/10.3390/molecules24142523  

   Smith, Ben E.; Carr, Jeremy M.; Tschumper, Gregory S. (July 2019, Molecules)

   A recent computational analysis of the stabilizing intramolecular OH⋯O contact in 1,2-dialkyl-2,3-epoxycyclopentanol diastereomers has been extended to thiiriane, aziridine and phosphirane analogues. Density functional theory (DFT), second-order Møller-Plesset perturbation theory (MP2) and CCSD(T) coupled-cluster computations with simple methyl and ethyl substituents indicate that electronic energies of the c i s isomers are lowered by roughly 3 to 4 kcal mol−1 when the OH group of these cyclopentanol systems forms an intramolecular contact with the O, S, N or P atom on the adjacent carbon. The results also suggest that S and P can participate in these stabilizing intramolecular interactions as effectively as O and N in constrained molecular environments. The stabilizing intramolecular OH⋯O, OH⋯S, OH⋯N and OH⋯P contacts also increase the covalent OH bond length and significantly decrease the OH stretching vibrational frequency in every system with shifts typically on the order of −41 cm−1. 

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4. Crystal structure of N , N -diisopropyl-4-methylbenzenesulfonamide

   https://doi.org/10.1107/S2056989020007185  

   Stenfors, Brock A.; Staples, Richard J.; Biros, Shannon M.; Ngassa, Felix N. (July 2020, Acta Crystallographica Section E Crystallographic Communications)

   The synthesis of the title compound, C 13 H 21 NO 2 S, is reported here along with its crystal structure. This compound crystallizes with two molecules in the asymmetric unit. The sulfonamide functional group of this structure features S=O bond lengths ranging from 1.433 (3) to 1.439 (3) Å, S—C bond lengths of 1.777 (3) and 1.773 (4) Å, and S—N bond lengths of 1.622 (3) and 1.624 (3) Å. When viewing the molecules down the S—N bond, the isopropyl groups are gauche to the aromatic ring. On each molecule, two methyl hydrogen atoms of one isopropyl group are engaged in intramolecular C—H...O hydrogen bonds with a nearby sulfonamide oxygen atom. Intermolecular C—H...O hydrogen bonds and C—H...π interactions link molecules of the title compound in the solid state. 

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5. Assessing the Possibility and Properties of Types I and II Chalcogen Bonds

   https://doi.org/10.3390/cryst13050766  

   Scheiner, Steve (May 2023, Crystals)

   Type I and II halogen bonds are well-recognized motifs that commonly occur within crystals. Quantum calculations are applied to examine whether such geometries might occur in their closely related chalcogen bond cousins. Homodimers are constructed of the R1R2C=Y and R1R2Y monomers, wherein Y represents a chalcogen atom, S, Se, or Te; R1 and R2 refer to either H or F. A Type II (T2) geometry wherein the lone pair of one Y is closely aligned with a σ-hole of its partner represents a stable arrangement for all except YH2, although not all such structures are true minima. The symmetric T1 geometry in which each Y atom serves as both electron donor and acceptor in the chalcogen bond is slightly higher in energy for R1R2C=Y, but the reverse is true for R1R2Y. Due to their deeper σ-holes, the latter molecules engage in stronger chalcogen bonds than do the former, with the exception of H2Y, whose dimers are barely bound. The interaction energies rise as the Y atom grows larger: S < Se < Te. 

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