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首页> 外文期刊>Journal of mass spectrometry: JMS >Change of the favored routes of EI MS fragmentation when proceeding from N~1, N~1-dimethyl-N~2-arylformamidines to 1,1,3,3-tetraalkyl-2-arylguanidines: Substituent effects
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Change of the favored routes of EI MS fragmentation when proceeding from N~1, N~1-dimethyl-N~2-arylformamidines to 1,1,3,3-tetraalkyl-2-arylguanidines: Substituent effects

机译：从N〜1，N〜1-二甲基-N〜2-芳基甲am转变为1,1,3,3-四烷基-2-芳基胍后EI MS裂解的有利途径的变化：取代作用

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摘要

Although series of N~1, N~1-dimethyl-N 2-arylformamidines and of 1,1,3,3-tetraalkyl-2-arylguanidines are structurally analogous and similar electron-ionization mass spectral fragmentationmay be expected, they display important differences in the favored routes of fragmentation andconsequently in substituent effectsonion abundances. In the caseof formamidines, the cyclizationelimination process (initiated by nucleophilic attack of the N-amino atom on the 2-position of the phenyl ring) and formation of the cyclic benzimidazolium [M-H]~+ ions dominates, whereas the loss of the NR2 group ismore favored for guanidines. In order to gain information on the most probable structures of the principal fragments, quantum-chemical calculations were performed on a selected set. A good linear relation between log{I[M-H]~+I [M]~(+?)} and σR~+ constants of substituent at para position in the phenyl ring occurs solely for formamidines (r = 0.989). In the case of guanidines, this relation is not significant (r = 0.659). A good linear relation is found between log{I[M-NMe_2]~+/I [M]~(+?)} and σp~+ constants (r = 0.993).
机译：尽管一系列N〜1，N〜1-二甲基-N 2-芳基甲am和1,1,3,3-四烷基-2-芳基胍在结构上相似并且可以预期相似的电子电离质谱碎裂，但它们显示出重要的差异在优选的断裂途径中，因此在取代基效应中离子丰度高。在甲am的情况下，环化消除过程（由苯环的2位上的N-氨基原子的亲核攻击引发）和环状苯并咪唑鎓[MH]〜+离子的形成占主导，而NR2基团的丢失胍更受青睐。为了获得有关主要片段的最可能结构的信息，对选定的一组进行了量子化学计算。仅对于甲am而言，log {I [M-H]〜+ I [M]〜（+？）}与苯环对位取代基的σR〜+常数之间具有良好的线性关系（r = 0.989）。在胍的情况下，这种关系不明显（r = 0.659）。在log {I [M-NMe_2]〜+ / I [M]〜（+？）}与σp〜+常数之间存在良好的线性关系（r = 0.993）。

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