title: Crystal structures of eight mono-methyl alkanes (C26-C32) via single-crystal and powder diffraction and DFT-D optimization.
abstract: 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, C26H54; (S)-9-methylheptacosane and (S)-11-methylheptacosane, C28H58; (S)-7-methylnonacosane, (S)-9-methylnonacosane, (S)-11-methylnonacosane and (S)-13-methylnonacosane, C30H62; and (S)-9-methylhentriacontane, C32H66. All crystallize in space group P21. 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.
authors: ESRF , CS 40220, 38043 Grenoble CEDEX 9, France ; School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University , Staffordshire ST5 5BG, UK.
authors: Lee
authors: L
authors: Brooks
authors: ILL , CS 20156, 38042 Grenoble CEDEX 9, France ; SNBL/ESRF , CS 40220, 38043 Grenoble CEDEX 9, France.
authors: Michela
authors: M
authors: Brunelli
authors: SNBL/ESRF , CS 40220, 38043 Grenoble CEDEX 9, France ; Crystallography Competence Centre, EPFL , 1015 Lausanne, Switzerland.
authors: Philip
authors: P
authors: Pattison
authors: School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University , Staffordshire ST5 5BG, UK.
authors: Graeme R
authors: GR
authors: Jones
authors: ESRF , CS 40220, 38043 Grenoble CEDEX 9, France.
authors: Andrew
authors: A
authors: Fitch
keywords: DFT-D; insect pheromones; mono-methyl alkanes; powder diffraction; single-crystal diffraction; synchrotron radiation