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The syntheses and characterization (NMR and XRD) of two substituted [2.2.2]bicyclooctene ring systems are described here. The cyclohexene rings of these systems adopt a nearly perfect boat conformation according to analysis using Cremer–Pople parameters. Both structures contain a nearly planar imide ring that is oriented endo relative to a bridgehead cyclopropyl ring. 4-(2-Phenylethyl)-4-azatetracyclo[5.3.2.02,6.08,10]dodec-11-ene-3,5-dione, C19H19NO2, is substituted with a phenylethyl group that hosts C—H...π interactions in the crystal. 4-[2-(4-Hydroxyphenyl)ethyl]-4-azatetracyclo[5.3.2.02,6.08,10]dodec-11-ene-3,5-dione, C19H19NO3, bears a 4-hydroxyphenylethyl group on the imide ring and contains O—H...O and C—H...O hydrogen bonds.

The present study evaluates the potential combination of charge‐transfer electron‐donor–acceptor π–π complexation and C—H hydrogen bonding to form colored cocrystals. The crystal structures of the red 1:1 cocrystals formed from the isomeric pyridines 4‐ and 3‐{2‐[4‐(dimethylamino)phenyl]ethynyl}pyridine with 1‐[2‐(3,5‐dinitrophenyl)ethynyl]‐2,3,5,6‐tetrafluorobenzene, both C14H4F4N2O4·C15H14N2, are reported. Intermolecular interaction energy calculations confirm that π‐stacking interactions dominate the intermolecular interactions within each crystal structure. The close contacts revealed by Hirshfeld surface calculations are predominantly C—H interactions with N, O, and F atoms. [ABSTRACT FROM AUTHOR]

This work explores the conformational preferences and the structure-property correlations of poly(butylene 2,5-furandicarboxylate) (PBF), a longer chain analogue of the most well-known biobased polyester from the furan family, poly(ethylene 2,5-furandicarboxylate) (PEF). A thorough computational spectroscopic study–including infrared, Raman and inelastic neutron scattering spectroscopy, combined with discrete and periodic density functional theory calculations–allowed the identification of dominant structural motifs in the amorphous and crystalline regions. Discrete calculations and vibrational spectroscopy of semi-crystalline and amorphous samples strongly support the predominance of gauche, trans, gauche conformations of the butylene glycol fragment in both the crystalline and amorphous domains. In what concerns the furandicarboxylate fragment, amorphous domains are dominated by syn,syn conformations, while in the crystalline domains the anti,anti forms prevail. A possible crystalline structure–built from these conformational preferences and including a network of C-H···O hydrogen bond contacts—was optimized using periodic density functional theory. This proposed crystal structure avoids the unrealistic structural features of the previously proposed X-ray structure, provides an excellent description of the inelastic neutron scattering spectrum of the semi-crystalline form, and allows the correlation between microscopic structure and macroscopic properties of the polymer.

The syntheses and crystal structures of the two title compounds, C11H10O3 (I) and C17H14BrNO2 (II), both containing the bicyclo[2.2.2]octene ring system, are reported here [the structure of I has been reported previously: White & Goh (2014). Private Communication (refcode HOKRIK). CCDC, Cambridge, England]. The bond lengths and angles of the bicyclo[2.2.2]octene ring system are similar for both structures. The imide functional group of II features carbonyl C=O bond lengths of 1.209 (2) and 1.210 (2) Å, with C—N bond lengths of 1.393 (2) and 1.397 (2) Å. The five-membered imide ring is nearly planar, and it is positioned exo relative to the alkene bridgehead carbon atoms of the bicyclo[2.2.2]octene ring system. Non-covalent interactions present in the crystal structure of II include a number of C—H...O interactions. The extended structure of II also features C—H...O hydrogen bonds as well as C—H...π and lone pair–π interactions, which combine together to create supramolecular sheets.

In the title compound, C20H18O4, the benzoate ring is oriented at an acute angle of 33.10 (12)° with respect to the planar (r.m.s deviation = 0.016 Å) coumarin ring system. An intramolecular C—H...O hydrogen bond closes an S(6) ring motif. In the crystal, C—H...O contacts generate infinite C(6) chains along the b-axis direction. Also present are π–π stacking interactions between neighbouring pyrone and benzene rings [centroid–centroid distance = 3.7034 (18) Å] and C=O...π interactions [O...centroid = 3.760 (3) Å]. The data obtained from quantum chemical calculations performed on the title compound are in good agreement with the observed structure, although the calculated C—O—C—C torsion angle between the coumarin ring system and the benzoate ring (129.1°) is somewhat lower than the observed value [141.3 (3)°]. Hirshfeld surface analysis has been used to confirm and quantify the supramolecular interactions.

The asymmetric unit of the title compound, C14H14O6, a monomeric compound of poly(butylene 2,5-furandicarboxylate), consists of one half-molecule, the whole all-trans molecule being generated by an inversion centre. In the crystal, the molecules are interconnected via C—H...O interactions, forming a molecular sheet parallel to (10\overline{2}). The molecular sheets are further linked by C—H...π interactions.

The molecule of the title Schiff base compound, C16H16N4O5S·C3H7NO, displays a trans conformation with respect to the C=N double bond. The C—N and N—N bonds are relatively short compared to their normal bond lengths, indicating some degree of delocalization in the molecule. The molecule is bent at the S atom, with an S—N—C—C torsion angle of 164.48 (11)°. The dihedral angle between the two aromatic rings is 84.594 (7)°. Intermolecular N—H...O and C —H...O hydrogen bonds connect centrosymmetrically related molecules into dimers forming rings of R33(11) and R22(10) graph-set motif stacked along the a axis into a columnar arrangement. The molecular columns are further linked into a three-dimensional network by C—H...π interactions.

In the title compounds, (2E,2′E)-3,3′-(1,4-phenylene)bis[1-(2-methoxyphenyl)prop-2-en-1-one], C26H22O4 (I), (2E,2′E)-3,3′-(1,4-phenylene)bis[1-(3-methoxyphenyl)prop-2-en-1-one], C26H22O4 (II) and (2E,2′E)-3,3′-(1,4-phenylene)bis[1-(3,4-dimethoxyphenyl)prop-2-en-1-one], C28H26O6 (III), the asymmetric unit consists of a half-molecule, completed by crystallographic inversion symmetry. The dihedral angles between the central and terminal benzene rings are 56.98 (8), 7.74 (7) and 7.73 (7)° for (I), (II) and (III), respectively. In the crystal of (I), molecules are linked by pairs of C—H...π interactions into chains running parallel to [101]. The packing for (II) and (III), features inversion dimers linked by pairs of C—H...O hydrogen bonds, forming R22(16) and R22(14) ring motifs, respectively, as parts of [201] and [101] chains, respectively.

The title compound, C22H28O3, was prepared by a direct acetylation reaction of naturally occurring totarolenone. The molecule contains three fused rings, which exhibit different conformations. The central ring has a half-chair conformation, while the non-aromatic oxo-substituted ring has a screw-boat conformation. In the crystal, molecules are linked by C—H...O hydrogen bonds and C—H...π interactions, forming sheets parallel to the bc plane. The carbonyl O atoms and the C atom at the 6-position of the cyclohexene ring are each disordered over two sets of sites with major occupancy components of 0.63 (7) and 0.793 (14), respectively.

In the title compound, C17H12O4, the benzoate ring is oriented at an acute angle of 60.14 (13)° relative to the coumarin plane (r.m.s. deviation = 0.006 Å). This conformation is stabilized by an intramolecular C—H...O weak hydrogen bond, which forms a five-membered ring. Also present are π–π stacking interactions between neighbouring pyrone and benzene rings [centroid-to-centroid distances in the range 3.6286 (1)–3.6459 (1) Å] and C=O...π interactions [O...centroid distances in the range 3.2938 (1)–3.6132 (1) Å]. Hirshfeld surface analysis has been used to confirm and quantify the supramolecular interactions.

In the title compound, C14H12ClNO2, the dihedral angle between the aromatic rings is 6.09 (17)° and the Car—C—C—Car torsion angle is −179.4 (3)°. The nitro group is close to coplanar with its attached ring [dihedral angle = 7.9 (2)°] and the Cl atom is disordered over two adjacent sites in a 0.54 (4):0.46 (4) ratio. In the crystal, C—H...O hydrogen bonds link the molecules into C(6) [001] chains.

The title carbazole derivative, C13H9NO, crystallizes with two independent molecules (A and B) in the asymmetric unit. The dihedral angle between the planar carbazole ring system and the aldehyde group (HC=O) is 3.3 (2)° in A and 7.5 (2)° in B, indicating that the molecules are both nearly planar. In the crystal, the A and B molecules are linked by a C—H...O hydrogen bond and stack along the b-axis direction. The structure was refined as a two component twin with a refined BASF value of 0.102 (2).

In the title compound, C18H12O6, the alkyne bonds are distorted, featuring bond angles around the C—C[triple-bond]C—C group of 173.6 (1)/179.0 (1), 178.1 (1)/178.4 (1) and 174.9 (1)/175.9 (1)°, and the ester groups make angles of 3.5 (1), 13.8 (1) and 14.5 (1)° with the central benzene ring. In the crystal, molecules are connected in layers parallel to (131) by weak C—H...O hydrogen bonds, giving rise to a system of hydrogen-bonded ring motifs with graph sets R22(14) and R44(22). The layers are linked by C—H...O and C—H...π contacts.

The asymmetric unit of the title compound, C14H11N3O2, contains two independent molecules linked by a C—H...O hydrogen bond. Pairs of neighboring dimeric units associate via π–π stacking interactions.

In the title compound, C30H20O2S2, the dihedral angles between the central azulene ring system (r.m.s. deviation = 0.039 Å) and the pendant benzene rings are 28.96 (7) and 55.15 (7)°. The dihedral angles between the benzene rings and their attached acetylsulfanyl groups are 59.60 (10) and 84.79 (10)°. The expected π–π stacking interactions are not observed in the crystal structure; instead, the packing features C—H...O hydrogen bonds, which link the molecules into C(12) [010] chains, which are supported by weak C—H...π contacts.

This work explores the conformational preferences and the structure-property correlations of poly(butylene 2,5-furandicarboxylate) (PBF), a longer chain analogue of the most well-known biobased polyester from the furan family, poly(ethylene 2,5-furandicarboxylate) (PEF). A thorough computational spectroscopic study-including infrared, Raman and inelastic neutron scattering spectroscopy, combined with discrete and periodic density functional theory calculations-allowed the identification of dominant structural motifs in the amorphous and crystalline regions. Discrete calculations and vibrational spectroscopy of semi-crystalline and amorphous samples strongly support the predominance of gauche, trans, gauche conformations of the butylene glycol fragment in both the crystalline and amorphous domains. In what concerns the furandicarboxylate fragment, amorphous domains are dominated by syn,syn conformations, while in the crystalline domains the anti,anti forms prevail. A possible crystalline structure-built from these conformational preferences and including a network of C-H···O hydrogen bond contacts-was optimized using periodic density functional theory. This proposed crystal structure avoids the unrealistic structural features of the previously proposed X-ray structure, provides an excellent description of the inelastic neutron scattering spectrum of the semi-crystalline form, and allows the correlation between microscopic structure and macroscopic properties of the polymer., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Nolasco, Rodrigues, Araújo, Coimbra, Ribeiro-Claro, Vaz, Rudić, Silvestre, Bouyahya, Majdoub and Sousa.)

Abstract: A density functional theory (DFT) study was carried out to calculate 17O, 14N and 2H electric field gradient (EFG) tensors in accurate neutron diffraction structures of α-glycine at 288 and 427 K. B3LYP is the used method and 6-311+G⁎ and 6-311++G⁎⁎ are the basis sets in the calculations of EFG tensors at the sites of 17O, 14N and 2H nuclei in the monomer and the octameric cluster of α-glycine at two temperatures. Quadrupole coupling constants and asymmetry parameters are the converted parameters of calculated EFG tensors to experimentally measurable ones. The calculated results of monomer and the target molecule in octameric cluster reveal that hydrogen-bonding interactions play an important role in the crystalline structure of α-glycine where the results of the target molecule in octameric cluster are in good agreement with the experiments. [Copyright &y& Elsevier]

An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from the author's laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the use α-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments andPro-Xxx segments for nucleating of β-hairpin structures. β- and γ-amino acid residues have been used to expand the range of designed polypeptide structures. [ABSTRACT FROM AUTHOR]