Article ID: 20130186
Anthracene–diacetylene cyclic dimers having two alkoxy groups (OMe, OEt, or OPr groups) at the intraannular positions were synthesized by dimerization of 1,8-diethynylanthracene precursors. For the OEt and OPr compounds, anti and syn stereoisomers that differed in the direction of the alkyl groups were separated by chromatography. Kinetic measurements showed that the barriers to isomerization from syn isomer to anti isomer were 124 and >146 kJ mol–1 for the OEt and OPr compounds, respectively. The molecular structures of these compounds were examined by X-ray analysis and DFT calculations. The preference for anti isomers is attributable to the intramolecular C–H⋯O hydrogen bonds. The effects of substituents on the molecular structures and the barriers to isomerization are discussed.
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