Preparations, crystal structures and DFT calculations of novel diacetylenes incorporating ynamine moieties

Two diacetylene molecules incorporating an ynamine moiety, 5-(diphenylamino)-2,4-pentadiyne-1-ol (1) and 6-(diphenylamino)-2-methylhexa-3,5-diyn-2-ol (2), were prepared and characterized by single crystal X-ray diffraction, 1H and 13C NMR. The crystal structures of 1 and 2 were solved successfully and were interpreted to be controlled mainly by the intermolecular hydrogen-bondings. The difference in the crystal structures between 1 and 2 was well explained by consideration of the steric repulsion with the methyl groups connected to the carbon atom adjacent to the hydroxyl group in 2. The steric effects of the methyl groups on intra and intercolumnar interaction were found to be important for designing molecular and crystal structures of diacetylene molecules. Although the geometries obtained by DFT calculations showed a good agreement on 2 except for the butadiynyl part, a significant difference was recognized at the environment around the nitrogen of 1. The difference could be explained by the effect of the crystal packing.