Role of weak C—H...O and strong N—H...O intermolecular interactions on the high-symmetry molecular packing of trans-cyclohexane-1,4-dicarboxamide

Abstract

An unpredicted fourfold screw N-HÁ Á ÁO hydrogen bond C(4) motif in a primary dicarboxamide (trans-cyclohexane-1,4-dicarboxamide, C 8 H 14 N 2 O 2 ) was investigated by single-crystal X-ray diffraction and IR and Raman spectroscopies. Electron-density topology and intermolecular energy analyses determined from ab initio calculations were employed to examine the influence of weak C-HÁ Á ÁO hydrogen-bond interactions on the peculiar arrangement of molecules in the tetragonal P4 3 2 1 2 space group. In addition, the way in which the co-operative effects of those weak bonds might modify their relative influence on molecular packing was estimated from cluster calculations. Based on the results, a structural model is proposed which helps to rationalize the unusual fourfold screw molecular arrangement.

Isosteric O/S exchange in carbonyl(thio)ureides: molecular interactions, structure, and bioactivity assays

“…7, right) and this interaction could be associated with a typical behavior of the carboxamide group (R-CO-NR′R′′). 67,68 The O3⋯H3 interaction (see Fig. S8, ESI†) also favors the formation of this centro-symmetric dimer with motif R 2 2 (14).…”

“…ρ ( r c ) and its Laplacian (∇ 2 ρ ( r c ) > 0 indicate that all BCPs of interest (Table 7) correspond to closed-shell interactions. 68,70,71 According to the analysis of the BCP distribution, S⋯S interactions are detected in the dimer A of I , which added to the C3–H⋯S and N–H1⋯S hydrogen contacts contribute to further stabilize the dimer. Disulfide bridges with comparable intermolecular contact geometry have been observed in other complexes, and they are also frequently found in protein stabilizing the 3D structure.…”

A dipole moment puzzle

“…In other solvents such as pyridine-d 5 and DMSO-d 6 , multiplets appeared, suggesting that, in solution at least, the structure was undergoing a dynamic conformational change; a fact that had been anticipated by Becker 12 and Vankorm. 5 On the other hand, crystallographic studies of all the members of this family showed that the individual molecules were centrosymmetric in the crystalline solid 10,[13][14][15][16][17][18] and would therefore have a zero dipole moment.…”

“…Preliminary semiempirical calculations 19 indicated that, although the dipole moments were essentially zero, the structure of these molecules showed a distinct deformation, especially in the cyclohexane ring, that appeared to give rise to chiral conformations. 18,[20][21][22] All this evidence is somewhat sketchy, and the dipole moment results give only a broad picture of the situation without much indication of its possible origin or the behavior of the molecules in solution. Indeed, it casts doubt on the assumption that the molecules are rigid species with well-defined structures that remain unchanged regardless of the medium they are in.…”