Crystal structures and solid-state reactivities of 1,4-and 1,2-bis(5-hydroxypenta-1,3-diynyl)benzenes and 1-(5-hydroxypenta-1,3-diynyl)-4-ethynylbenzene

Crystal structures and the solid-state polymerization of 1,4-bis(5-hydroxyp enta-1,3-diynyl)benzene (1), 1,2-bis(5-hydroxypenta-1,3-diynyl)benzene (2) and 1-(5-hydroxypenta-1,3-diynyl)-4-ethynylbenzene (3) were investigated. T he crystal structure of 1 depends on the recrystallization solvent. Crystal s obtained from acetone-benzene mixtures polymerize when irradiated with ga mma-rays or heated. The colourless crystals become black and are insoluble in common organic solvents. Only one of the butadiynyl groups participates in the radiation-induced polymerization, whereas both do, in the thermal po lymerization. Polymerization does not occur for crystals obtained from pure acetone. The polymerization reactivities are correlated to the crystal str uctures. Polymerizable crystals were not obtained from 2. The arrangement o f the butadiynyl groups in crystals of 2 is unfavorable for the polymerizat ion. Crystals of 3, obtained from hexane-acetone mixtures, polymerize upon gamma-irradiation but not upon heating. In the radiation-induced polymeriza tion of 3, the propagation by the ethynyl and butadiynyl groups is consider ed to proceed independently along different crystal axes. The ethynyl group s are more reactive than the butadiynyl groups because they have a shorter intermolecular carbon-carbon distance through which the polymerization occu rs. The difference in reactivity toward heating between 1 and 3 may also be interpreted in terms of intermolecular carbon-carbon distances of the buta diynyl groups.