电子等排体的噻吩多烯与苯多烯同系递变的比较I

为了进一步研究苯多烯化合物的电子等排体噻吩多烯化合物的结构与性能间的定量关系,确定噻吩基的端基当量,合成了三个末端带拉电子基团的噻吩多烯化合物,测定了它们在乙醇和环己烷中的电子光谱,结果表明,和相应苯多烯化合物的电子光谱相比 ,普通红移25-30nm,即相差一个插烯双键引起的红移.以2-噻吩基的端基当量为3,噻吩多烯化合物的电子光谱波数与同系因子(1/2)^2^/^N形成良好的直线,相关系数r>0.99;并与相应苯多烯化合物的同系直线相距很近.其差距可用苯多烯系列增加一个烯链的增量与改换一个电子等排体2-噻吩基的增量之比作定量描述.结果证明2-噻吩基的端基当量比苯基大.

A comparison of homologous gradation for isosteric thienyl-and phenylpolyene series I.

Three series of 2-thienylpolyenic compounds I (R = Ac, CO2Et, cyano; n = 0-4) have been synthesized. Their electronic absorption spectra are compared with those of the corresponding isosteric phenylpolyenic series. When compared with the Ph compounds, the electronic absorption peaks of I are all red-shifted by about 25-30 nm, being about the increase in wavelength caused by lengthening a phenyl-polyenic chain by one unit. If the equivalent of the 2-thienyl group is taken as 3 instead of 2, the electronic absorption peaks of I conform to the rule of homologous linearity with correlation coefficients >0.99. In addition, the homologous line for the 2-thienyl series lies very close to that of the Ph series. The difference between the two lines, represented quant. by the ratio DlTh/DlE, is quite close to unity, where DlTh is the increment of the wavelength caused by the replacement of a Ph group by an isosteric 2-thienyl ring, and DlE is the increment by lengthening the phenyl-polyenic chain by one ethylenic unit.