A systematic survey of the Cambridge Structural Database (CSD) has identified all intramolecular hydrogen-bonded ring motifs comprising less than 20 atoms with N and O donors and acceptors. The probabilities of formation P(m) of the 50 most common motifs, which chiefly comprise five- and six-membered rings, have been derived by considering the number of intramolecular motifs which could possibly form. The most probable motifs (P(m) > 85%) are planar conjugated six-membered rings with a propensity for resonance-assisted hydrogen bonding and these form the shortest contacts, whilst saturated six-membered rings typically have P(m) < 10%. The influence of intramolecular-motif formation on intermolecular hydrogen-bond formation has been assessed for a planar conjugated model substructure, showing that a donor-H is considerably less likely to form an intermolecular bond if it forms an intramolecular one. On the other hand, the involvement of a carbonyl acceptor in an intramolecular bond does not significantly affect its ability to act as an intermolecular acceptor and thus carbonyl acceptors display a substantially higher inclination for bifurcation if one hydrogen bond is intramolecular.

Two polymorphs (A and B) of trans-1,4-diethynylcyclohex-ane-1,4-diol represent a unique example of the simultaneous occurrence of both conformational polymorphism and conformational isomorphism, while a pseudopolymorphic monohydrate is closely related.

Experimental and theoretical data indicate a preferred conformation for N--fluoroethylamides in which the C-F and C-N(CO) bonds are gauche rather than anti to each other. Theoretical calculations on a model system predict the gauche conformation to be 1.8 kcal mol ؊1 lower in energy than the anti conformation. This compares with a value of 0.7 kcal mol ؊1 for the gauche effect in 1,2difluoroethane.

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Molecules of the title compound, C(16)H(14)O, are chiral and crystallize in space group P-4 with Z' = 2, and with one R and one S molecule in the asymmetric unit. The conformations of the phenyl rings in the two independent molecules differ slightly. Supramolecular organization in the crystal is via tetrameric O-H. H(O) hydrogen-bonded synthons formed separately by each conformer. These tetrameric synthons stack along the c axis via C[triple-bond]C-H.O(H) hydrogen bonds. The only link between the conformer stacks is provided by weaker C(methylene)-H and C(phenyl)-H interactions with pi(arene) density.

The title saccharinate complexes, aqua[1,2‐benzisothiazol‐3(2H)‐onato 1,1‐dioxide‐N]bis(1,10‐phenanthroline‐N,N′)man­ganese(II) 1,2‐benz­isothia­zol‐3(2H)‐onate 1,1‐dioxide,[Mn(C7H4NO3S)(C12H8N2)2(H2O)](C7H4NO3S), and aqua[1,2‐benz­iso­thiazol‐3(2H)‐onato 1,1‐dioxide‐N]­bis­(2,2′‐bi­pyri­dine‐N,N′)­cobalt(II) 1,2‐benz­iso­thia­zol‐3(2H)‐onate 1,1‐di­oxide, [Co­(C7H4NO3S)­(C10H8N2)2­(H2O)]­(C7H4NO3S), have been prepared and their crystal structures determined at 150 K. The structure of the manganese complex consists of repeated alternating [Mn(phen)2(sac)(H2O)]+ cations and non‐coordinated saccharinate anions. The water molecule, bound to manganese as part of a slightly distorted octahedral arrangement, is hydrogen bonded to an O atom of the SO2 group in the saccharinate counter‐ion. In contrast, the cobalt complex has one pseudo‐octahedral [Co(bipy)2(sac)(H2O)]+ cation, with the cobalt‐bound water molecule hydrogen bonded to the N atom of the accompanying free saccharinate anion.

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The structures of four para-substituted derivatives of diphenylethynylmethanol have been determined [ditolylethynylmethanol, di(4-chlorophenyl)ethynylmethanol, di(4-bromophenyl)ethynylmethanol and bis(4,4′-biphenylyl)ethynylmethanol]. The dimethyl, dichloro, dibromo and diphenyl compounds have been analysed using X-ray diffraction at 150 K, and the dichloro compound has also been studied using neutron diffraction at 150 K. In common with the parent diphenylethynylmethanol [Garcia, Ramos, Rodriguez & Fronczek (1995). Acta Cryst. C51, 2674–2676], all four derivatives fail to form the expected strong O—H...O hydrogen bonds due to steric hindrance. Instead, the supramolecular structural organization in this family of gem-alkynols is mediated by a variety of weaker interactions. The two most acidic protons, O—H and C[triple-bond]C—H, participate in weak hydrogen bonds to π-acceptors, forming synthons that stabilize all five structures. These primary interactions are reinforced by a variety of other weak hydrogen bonds involving C—H donors and the hydroxy-O as an acceptor, and by halogen...halogen interactions in the dichloro and dibromo compounds.