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Unexpected beauty and diversity in the structures of three homologous 4,5‐dialkoxy‐1‐ethynyl‐2‐nitrobenzenes: the subtle interplay between intermolecular C—H…O hydrogen bonds and alkyl chain length
Author(s) -
Oburn Shalisa M.,
Bosch Eric
Publication year - 2017
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229617012761
Subject(s) - triclinic crystal system , monoclinic crystal system , crystallography , crystal structure , hydrogen bond , chemistry , stereochemistry , alkoxy group , molecule , nitro , intermolecular force , alkyl , organic chemistry
The synthesis, 1 H and 13 C NMR spectra, and X‐ray structures are described for three dialkoxy ethynylnitrobenzenes that differ only in the length of the alkoxy chain, namely 1‐ethynyl‐2‐nitro‐4,5‐dipropoxybenzene, C 14 H 17 NO 4 , 1,2‐dibutoxy‐4‐ethynyl‐5‐nitrobenzene, C 16 H 21 NO 4 , and 1‐ethynyl‐2‐nitro‐4,5‐dipentoxybenzene, C 18 H 25 NO 4 . Despite the subtle changes in molecular structure, the crystal structures of the three compounds display great diversity. Thus, 1‐ethynyl‐2‐nitro‐4,5‐dipropoxybenzene crystallizes in the trigonal crystal system in the space group , with Z = 18, 1,2‐dibutoxy‐4‐ethynyl‐5‐nitrobenzene crystallizes in the monoclinic crystal system in the space group P 2 1 / c , with Z = 4, and 1‐ethynyl‐2‐nitro‐4,5‐dipentoxybenzene crystallizes in the triclinic crystal system in the space group , with Z = 2. The crystal structure of 1‐ethynyl‐2‐nitro‐4,5‐dipropoxybenzene is dominated by planar hexamers formed by a bifurcated alkoxy sp ‐C—H…O,O′ interaction, while the structure of the dibutoxy analogue is dominated by planar ribbons of molecules linked by a similar bifurcated alkoxy sp ‐C—H…O,O′ interaction. In contrast, the dipentoxy analogue forms ribbons of molecules alternately connected by a self‐complementary sp ‐C—H…O 2 N interaction and a self‐complementary sp 2 ‐C—H…O 2 N interaction. Disordered solvent was included in the crystals of 1‐ethynyl‐2‐nitro‐4,5‐dipropoxybenzene and its contribution was removed during refinement.