How the Chalcogen Atom Size Dictates the Hydrogen‐Bond Donor Capability of Carboxamides, Thioamides, and Selenoamides

Abstract

The amino groups of thio-and selenoamides can act as stronger hydrogen-bond donors than of carboxamides, despite the lower electronegativity of S and Se. This phenomenon has been experimentally explored, particularly in organocatalysis, but a sound electronic explanation is lacking. Our quantum chemical investigations show that the NH 2 groups in thio-and selenoamides are more positively charged than in carboxamides. This originates from the larger electronic density flow from the nitrogen lone pair of the NH 2 group towards the lower-lying π* C=S and π* C=Se orbitals than to the high-lying π* C=O orbital. The relative energies of the π* orbitals result from the overlap between the chalcogen np and carbon 2p atomic orbitals, which is set by the carbonchalcogen equilibrium distance, a consequence of the Pauli repulsion between the two bonded atoms. Thus, neither the electronegativity nor the often-suggested polarizability but the steric size of the chalcogen atom determines the amide's hydrogen-bond donor capability.

Strengthened cooperativity of DNA-based cyclic hydrogen-bonded rosettes by subtle functionalization

“…24 Previous studies have proved the reliability of this level of theory for the evaluation of the hydrogen bonding interaction mechanism within weakly-bound complexes. [25][26][27] The bonding energies of the hexamers, as well as their subunits, i.e., dimers, trimers, tetramers and pentamers, were computed using eqn (1):…”

“…The electron charge distribution has been analyzed within the Voronoi Deformation Density (VDD) analysis. 4,30 Fig. 1 Structure of a G-C Janus-type monomer, referred to as AAD in the present study (left), and the schematic structure of the rosette derived from the AAD monomer (right).…”

“…An interesting functionalization at the supramolecular level is the capability of cooperativity between hydrogen-bonded structures. [1][2][3][4][5] Taking into consideration the spatial disposition of cooperative molecules, mainly there are two different kinds of studied hydrogen-bonded systems with specific capabilities or properties related to their arrangement, thus being either linearly [6][7][8][9][10] or cyclically cooperative. 1,[11][12][13] With respect to the latter, lately the so-called rosette structures or cyclic hexamers have gained interest.…”

Understanding the influence of alkali cations and halogen anions on the cooperativity of cyclic hydrogen‐bonded rosettes in supramolecular stacks

“…[21] based on dispersion‐corrected relativistic density functional theory at the ZORA‐BLYP‐D3/TZP level for geometry optimizations and ZORA‐BLYP‐D3/TZ2P for energies. Previous works[ 22 , 23 , 24 ] have shown that this level of theory gives excellent understanding of bonding mechanism in hydrogen bonding and also in long range interactions within weakly‐bound complexes. [11] Furthermore, the use of the TZP basis set for large supramolecular systems has shown to furnish accurate results.…”

Molecular Recognition Studies of Thioamide (−CSNH2) Functionality through Co-crystals of Some Thiobenzamides with N-Donor Ligands: Evaluation and Correlation of Structural Landscapes with Morphology and Lattice Energy

“…In all these complexes, nevertheless, hydrogen bond acceptor is an O atom, the prime member of the chalcogen group. , In recent times, attention was drawn to the other chalcogens also but mostly pertained to Se, Te, etc., especially to evaluate competitiveness with respect to halogen bonding. However, there has only been a little focus on S-based supramolecular assemblies despite the fact that such compounds are so much well known for their significance in various biological processes in the form of peptides and also as precursors for many chemical transformations in the domains of natural product synthesis, bioinorganic complexes, polymers, etc.…”