两类氟代对三联苯液晶化合物的质谱裂解规律分析

Fragmentation Rules for Two Kinds of Fluoro-p-terphenyl Liquid Crystalline Compounds

利用气相色谱-质谱联用法(GC/MS)对两类氟代对三联苯共12个液晶化合物进行电子轰击离子化(EI)质谱分析,并总结其裂解规律。氟代对三联苯液晶化合物的主要裂解过程是苄基裂解失去烷基,某些碎片离子会违背偶电子规则进一步生成m/z 274碎片离子。氟原子取代位置会对裂解产生一定的影响,由于氟原子的吸电子诱导效应,在某种程度上改变了对三联苯之间的共轭度,碎片离子的相对丰度会有明显差异。

The EI mass spectra of two kinds of fluoro-p-terphenyl liquid crystalline com- pounds （FTPLCCs） were analyzed by gas chromatogram-mass spectrometry （GC/MS）, and the fragmentation rules of FTPLCCs were summarized. The main fragmentation pathways of FTPLCCs are the loss of an alkyl from the molecular ions via benzyl cleav- age. The fragmental ion at m/z 274 can be produced from some other bigger fragmental ions, which is contrary to the even electron rule. The position of fluorine atom has some influence on the fragmentation pathways of FTPLCCs. The relative abundances of the fragmental ions have obvious differences caused by the electron-withdrawing inductive effect of fluorine atom and resulting alternation of the conjugation degree of the terphe- nyl moieties.