Normalized parameters are presented to assist the interpretation of crystal mechanisms of a series of triazene N1-oxides. The role of halogen⋯π interactions is discussed.

Rotaxanes are designated as molecular machines due their different movements. Systematic studies regarding the different conformations adopted by these systems and the factors that lead to the distribution of the conformations, in both solution and the solid state, have not been widely explored, especially for rotaxanes with nonsymmetric stoppers. Therefore, in this study we have investigated three novel [2]rotaxanes containing threads derived from nonsymmetric succinamides [R1R2NC(O)‐CH2CH2‐C(O)NR2R1, with R1/R2 = Bu/Bn, Bu/2‐furylmethyl, and 5‐methylisoxazol‐3‐yl/2‐furylmethyl]. The proportions of rotamers were investigated for threads and rotaxanes by solution and solid‐state NMR spectroscopy as well as by single‐crystal and powder X‐ray diffraction. In solution, the threads present different proportions of conformer, with the E,Z conformation prevailing, whereas only one conformer is observed in the solid state. For the rotaxanes, only one conformer prevails in the single crystal, whereas the solution and solid (bulk) states present more than one rotamer. These proportions are modified when the threads are incorporated into the macrocycle during rotaxane formation. The intramolecular interactions in each rotamer were investigated by QTAIM and variable‐temperature 1H NMR experiments. The changes in conformational population between the threads and respective rotaxanes can be explained by a set of different intramolecular interactions, with trifurcated hydrogen bonds responsible for most of the stabilization energy.

A series of seven N -phenylamides [R–C(O)NHPh, in which R: CH 3 , C(CH 3 ) 3 , Ph, CF 3 , CCl 3 , CBr 3 , and H] were used as models in this study. Molecular packing and intermolecular interactions were evaluated by theoretical calculations, solution NMR, and quantum theory of atoms in molecules analyses. Crystallization mechanisms were proposed based on the energetic and topological parameters using the supramolecular cluster as demarcation. Concentration-dependent 1 H NMR experiments corroborated the proposed interactions between molecules. For all compounds (except for R: H, which initially formed tetramers), layers (two-dimensional) or chains (one-dimensional) were formed in the first stage of the proposed crystallization mechanisms. The presence of strong intermolecular NH···O=C interactions promoted the first stages. The study in solution provided different values of association constant ( K ass ) governed by the hydrogen bond NH···O=C, showing that the stronger interactions are directly influenced by the substituent steric hindrance. A correlation between K ass(NH···O=C) from the solution and the NH···O=C interaction energy in the crystal showed a good trend.

Insights into the occurrence of packing and conformational polymorphs and anhydrous/hydrate forms of 1,2-bis­(aminocarbonyl­(1-tert-butyl-1H-pyrazol-[3]­5-yl))­ethanes with the substituents R = Me (a), F-4-Ph (b), Cl-4-Ph (c), and Br-4-Ph (d) in positions 5 (1) and 3 (2) of the pyrazole rings are presented. In this series, two molecular forms were observed, linear and folded. Compound 1a revealed an illuminating and rare example of a highly flexible molecule with packing polymorphism. The molecular stacking and absence of NH···OC interactions promoted polymorph growth. Structure 2a showed chains driven by NH···OC bonds in the anhydrous form and closed dimers by water binding the molecules (NHamide···OHwt···COamide) in the hydrate form. Two different forms were observed for conformational polymorph 2d (linear and folded). The folded form was about −10 kcal mol–1 more stable than the linear form, showing significant crystalline packing differences. This occurrence is attributed to the rotation of the amide groups through the NH···OC bonds. The linear shape showed a higher stabilization energy for NH···OC bonds and a cluster −6 kcal mol–1 more stable than polymorph 2dI. Compounds 1b–d and 2b-c also had their crystal growth proposed and features highlighted.

The conformation adopted by COOEt group in solid state were influenced by supramolecular environment and intramolecular interaction for 1,3- and 1,5-regioisomers, respectively.

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A series of N-arylbenzamides containing amide group and phenyl−perfluorinated rings were used as the smallest molecules to investigate the direct influence of hydrogen bond and aromatic donor-acceptor complementarity in the...

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