Acta Crystallographica Section C

Crystal Structure Communications

Volume 64, Part 2 (February 2008)

organic compounds

Acta Cryst. (2008). C64, o33-o36 [ doi:10.1107/S0108270107065523 ]

Three 2,5-dialkoxy-1,4-diethynylbenzene derivatives

J. Figueira, J. Rodrigues, L. Russo and K. Rissanen

Abstract: 2,5-Diethoxy-1,4-bis[(trimethylsilyl)ethynyl]benzene, C₂₀H₃₀O₂Si₂, (I), constitutes one of the first structurally characterized examples of a family of compounds, viz. the 2,5-dialkoxy-1,4-bis[(trimethylsilyl)ethynyl]benzene derivatives, used in the preparation of oligo(phenyleneethynylene)s via Pd/Cu-catalysed cross-coupling. 2,5-Diethoxy-1,4-diethynylbenzene, C₁₄H₁₄O₂, (II), results from protodesilylation of (I). 1,4-Diethynyl-2,5-bis(heptyloxy)benzene, C₂₄H₃₄O₂, (III), is a long alkyloxy chain analogue of (II). The molecules of compounds (I)-(III) are located on sites with crystallographic inversion symmetry. The large substituents either in the alkynyl group or in the benzene ring have a marked effect on the packing and intermolecular interactions of adjacent molecules. All the compounds exhibit weak intermolecular interactions that are only slightly shorter than the sum of the van der Waals radii of the interacting atoms. Compound (I) displays C-H [pi] interactions between the methylene H atoms and the acetylenic C atom. Compound (II) shows [pi] - [pi] interactions between the acetylenic C atoms, complemented by C-H [pi] interactions between the methyl H atoms and the acetylenic C atoms. Unlike (I) or (II), compound (III) has weak nonclassical hydrogen-bond-type interactions between the acetylenic H atoms and the ether O atoms.

Formula: C₂₀H₃₀O₂Si₂, C₁₄H₁₄O₂ and C₂₄H₃₄O₂


	Structure factor file (CIF format) (97.9 kbytes) [ doi:10.1107/S0108270107065523/sk3181Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (50.7 kbytes) [ doi:10.1107/S0108270107065523/sk3181IIsup3.hkl ] Contains datablock II

	Structure factor file (CIF format) (92.6 kbytes) [ doi:10.1107/S0108270107065523/sk3181IIIsup4.hkl ] Contains datablock III

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