School of Chemistry and Biosciences, 123019Faculty of Life Sciences, 1905University of Bradford, Bradford, UK.
Eur J Mass Spectrom (Chichester). 2023 Apr;29(2):75-87. doi: 10.1177/14690667231153777. Epub 2023 Feb 16.
The electron ionisation mass spectra of an extensive set of 53 ionised monosubstituted and disubstituted cinnamamides [XCHCH=CHCONH, X = H, F, Cl, Br, I, CH, CHO, CF, NO, CHCH, (CH)CH and (CH)C; and XYCHCH=CHCONH, X = Y = Cl; and X, Y = F, Cl or Br] are reported and discussed. Particular attention is paid to the significance of loss of the substituent, X, from the 2-position, via a rearrangement that is sometimes known as a proximity effect, which has been reported for a range of radical-cations, but is shown in this work to be especially important for ionised cinnamamides. When X is in the 2-position of the aromatic ring, [M - X] is formed to a far greater extent than [M - H]; in contrast, when X is in the 3-position or 4-position, [M - H] is generally much more important than [M - X]. Parallel trends are found in the spectra of XYCHCH=CHCONH: the signal for [M - X] dominates that for [M - Y] when X is in the 2-position and Y in the 4-position or 5-position, irrespective of the nature of X and Y. Further insight is obtained by studying the competition between expulsion of X and alternative fragmentations that may be described as simple cleavages. Loss of NH results in the formation of a substituted cinnamoyl cation, [XCHCH=CHCO] or [XYCHCH=CHCO]; this process competes far less effectively with the proximity effect when X is in the 2-position than when it is in the 3-position or 4-position. Additional information has been obtained by investigating the competition between formation of [M - H] by the proximity effect and loss of CH by cleavage of a 4-alkyl group to give a benzylic cation, [RRCCHCH=CHCONH] (R, R = H, CH).
报道并讨论了广泛的 53 种离子单取代和双取代肉桂酰胺[XCHCH=CHCONH，X = H、F、Cl、Br、I、CH、CHO、CF、NO、CHCH、（CH）CH 和（CH）C；和 XYCHCH=CHCONH，X = Y = Cl；和 X、Y = F、Cl 或 Br]的电子离子化质谱。特别关注了取代基 X 通过重排从 2 位失去的意义，这种重排有时被称为邻位效应，已报道了一系列自由基阳离子，但在这项工作中表明，对于离子化肉桂酰胺，这种效应尤其重要。当 X 在芳环的 2 位时，[M - X]的形成程度远远大于[M - H]；相反，当 X 在 3 位或 4 位时，[M - H]通常比[M - X]重要得多。在 XYCHCH=CHCONH 的光谱中也发现了类似的趋势：当 X 在 2 位而 Y 在 4 位或 5 位时，[M - X]的信号比[M - Y]的信号强得多，无论 X 和 Y 的性质如何。通过研究取代基 X 的排出和可能被描述为简单裂解的替代断裂之间的竞争，可以获得进一步的见解。失去 NH 导致形成取代的肉桂酰阳离子[XCHCH=CHCO]或[XYCHCH=CHCO]；当 X 在 2 位时，这个过程与邻位效应的竞争比 X 在 3 位或 4 位时要小得多。通过研究通过邻位效应形成[M - H]和通过裂解 4-烷基基团形成苄基阳离子[RRCCHCH=CHCONH]（R，R = H，CH）来竞争失去 CH 的过程，获得了更多的信息。
