Cyclic Acetylenes. XIII. The Syntheses and Properties of p,p′-Bridged Cyclic Diphenyldiacetylenes

Concerning the studies on the effect of ring strain on the electronic spectra of cylcic acetylenes, a series of polymethylene ether derivatives of p,p′-dihydroxydiphenyldiacetylene (VIn, n=13, 14, 15, and 18) has been prepared by the oxidative coupling of p-hydroxyphenylacetylene polymethylene ethers (Vn, n=13, 14, 15, and 18) under a high dilution condition. A slight bathochromic shift accompanied by hypochromism was observed in the electronic spectra of VIn resulting from the increase of the ring strain. The same trend has been observed in the p,p′-bridged cyclic tolans. However, the bathochromic shift observed in the p,p′-series makes a contrast with the hypsochromic shift in the strained o,o′-bridged cyclic diphenyldiacetylene (I) and o,p′-bridged cyclic tolans (II). The NMR and IR spectra of VIn were discussed.