The crystal structures of eight mono-methyl alkanes have been determined from single-crystal or high-resolution powder X-ray diffraction using synchrotron radiation. Mono-methyl alkanes can be found on the cuticles of insects and are believed to act as recognition pheromones in some social species, e.g. ants, wasps etc. The molecules were synthesized as pure S enantiomers and are (S)-9-methylpentacosane, C 26 H 54 ; (S)-9-methylheptacosane and (S)-11-methylheptacosane, C 28 H 58 ; (S)-7-methylnonacosane, (S)-9-methylnonacosane, (S)-11-methylnonacosane and (S)-13-methylnonacosane, C 30 H 62 ; and (S)-9-methylhentriacontane, C 32 H 66. All crystallize in space group P2 1 . Depending on the position of the methyl group on the carbon chain, two packing schemes are observed, in which the molecules pack together hexagonally as linear rods with terminal and side methyl groups clustering to form distinct motifs. Carbon-chain torsion angles deviate by less than 10 from the fully extended conformation, but with one packing form showing greater curvature than the other near the position of the methyl side group. The crystal structures are optimized by dispersion-corrected DFT calculations, because of the difficulties in refining accurate structural parameters from powder diffraction data from relatively poorly crystalline materials.
Data of these crystal was collected by the use of. Stoe IPDS II diffractometer system. Crystal structure were solved by direct methods. Sır97 structure solution program was used. A refinement was carried out by full -matrix least -squares methods using Shelxl 97 refinement program. Fig 1:An ORTEP-III view of title compound [1] Ates¸, Ö ., Cesur, N., Güner, H., Uzun, M., Kiraz, M. & Kaya, D., Farmaco, 1995, 50, 361-364. [2] Günay, N. S., Çapan, G., Ulusoy, N., Ergenç, N., Öztürk, G. & Kaya, D., Farmaco, 1999, 54, 826-831 Complexes of para disubstituted and 4-monosubstituted biphenyl formed with 4,4'-dinitrobiphenyl (DNBP), demonstrate intense colours, from pale yellow to dark red, upon formation. These colours are dissimilar to the colour combination of the parent compounds. The focus of this study was to investigate the nature of these molecular donoracceptor interactions in the solid state, using spectroscopic techniques such as IR, Raman, UV-Vis, NMR and X-ray crystallography. Typical interactions observed in such molecular complexes include π-π interactions, hydrogen bonding, charge transfer and van der Waals interactions. There are no significant localized interactions between the guest molecule and the DNBP, except for the weak H-bond observed in the hydroxybiphenyl complex [1]. Complexes of DNBP, as acceptor, studied included a variety of mono-and disubstituted donors, such as dihalo, diamino, di-and monohydroxy groups. The crystal structures of these complexes showed retention of the non-planar conformation of DNBP with a dihedral angle of around 35 O . This conformation for DNBP has also been confirmed using density functional theory (Guassian) calculations that showed good agreement between the theoretically calculated and experimentally observed IR and Raman spectra in the solid state. In non-complexed DNBP, adjacent stacks of DNBP imolecules form a herring-bone pattern when viewed from above. On forming complexes with planar guest molecules, the stacks open out to form a checker-board pattern (as viewed from above) forming slots between the stacks which are occupied by the guest molecules. The packing is generally similar in all the complexes with planar guest molecules and is determined by the stacking of the DNBP molecules -with the substituted biphenyls, urea [2] or thiourea guest molecules slotting in between the stacks. It appears as if the packing of the complexes in the solid state is directed mainly by the similar packing of DNBP units in these complexes. Some of the molecular ratios for these complexes that vary, depending on the electronic properties of the donor molecules, were determined using NMR spectroscopy. The ratio of guest to DNBP depends on the size (length) of the guest molecule.[1]C.P.Brock, K.L.Haller Acta Crystallogr. Sect.C, C: Cryst. Struct Commun.,1984, 40, 1387 Pheromones are widely recognised as being extremely important among social insects as a means of communication [1]. They can be both volatile and non-volatile chemicals, which can act by simple detection in th...
Poster Sessions of organic azo pigments; it serves as a linker between two azo moieties [1]. Despite of its commercial importance, crystal structures of 1 are not known up to now. We were able to grow crystals from 1-butanole using re-crystallisation techniques. The X-ray structure analysis showed that the crystal was a monohydrate of 1. We dried the powder of 1 at 120 and measured its X-ray powder pattern. The powder was monophasic and we were able to determine the structure from the powder pattern using DASH [2] and TOPAS [3]. This polymorph turned out to be the anhydrous form. A third polymorphic form was obtained by drying the mono-hydrate at 70 C. The resulting powder pattern contained eight reflexions only, and the crystal structure could not been solved yet. [1] W.
Eight chiral monomethyl alkanes have been synthesized and their crystal structures solved from high resolution powder diffraction patterns collected using synchrotron radiation. Such compounds have been seen to act as recognition pheromones in social insects. Carbon chain lengths varied from C25to C31with the methyl group at various positions along the chain. One compound, (S)-7-methylnonacosane, also formed a low quality single crystal from which its structure was solved and refined. Although the powder diffraction patterns were good enough to solve the crystal structures, using the standard technique of real-space simulated annealing, with near-linear molecules, chemically unreasonable distortions occurred during Rietveld refinement unless many distance, angle and torsion restraints were imposed. From the results of the single-crystal structure it is evident that there is a gentle bend in the molecule close to the position of the methyl side chain. Thus imposing a near-linear molecule is incorrect, and giving sufficient freedom in the Rietveld refinement to allow the molecule to bend leads to an inaccurate structure. In short, the correct structure must be known to judge the strength of the restraints to apply, and this must vary at different parts of the chain. As an alternative to refining the structure from the powder diffraction data, the structures have been optimized via dispersion-corrected DFT calculations (Van der Streek and Neumann, 2010) starting from the powder structures. Agreement between the single-crystal and DFT-minimized structures is satisfactory, with an rms distance of 0.054 Å and a maximum distance of 0.132 Å when comparing carbon atoms positions. With this approach, a well defined structure optimization strategy is used for all the crystal structures. The molecules studied fall into two packing types, (both with monoclinic symmetry), depending on the position of the methyl group on the main carbon chain relative to the overall chain length.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.