Chemistry and Chemical Technology, University of Bradford, BD7 1DP, Bradford, West Yorkshire, England.
J Am Soc Mass Spectrom. 1996 Feb;7(2):205-8. doi: 10.1016/1044-0305(95)00679-6.
The recent proposal that ionized phytyl methyl ether [C16H33(CH3)C=CHCH2OCH 3 (+·) ] undergoes an allylic rearrangement to ionized isophytyl methyl ether [CH2=CHC(C16H33)(CH3)OCH 3 (+·) ] before elimination of an alkyl radical is discussed. Both literature precedent and new results in which the structure of the M-C16H 33 (·) fragment ion is established by comparison of its collision-induced dissociation mass spectrum with the spectra of isomeric C5H9O(+) ions of known structure are inconsistent with this proposal. The forma Hon of CH3CH=CHCH=O(+)CH3 by loss of a γ-alkyl substituent without skeletal isomerization rather than CH2=CHC(CH3)=O(+)CH3 after allylic rearrangement is explained in terms of a mechanism that involves two 1,2-H shifts, followed by σ-cleavage of the resultant ionized enol ether, C16H33(CH3)CH-CH=CHOCH 3 (+·) .
最近有人提出，在消除烷基自由基之前，[C16H33(CH3)C=CHCH2OCH3 (+·)]发生烯丙基重排生成[CH2=CHC(C16H33)(CH3)OCH3 (+·)]。文献先例和新结果都表明，通过比较M-C16H33(·)片段离子的碰撞诱导解离质谱与已知结构的异构 C5H9O(+)离子的光谱，可以确定该片段离子的结构，这与上述提议不一致。没有骨架异构化，而是通过γ-烷基取代基的消除形成 CH3CH=CHCH=O(+)CH3，而不是经过烯丙基重排后形成 CH2=CHC(CH3)=O(+)CH3，可以用涉及两个 1,2-H 转移的机理来解释，随后是所得烯醇醚的σ断裂，C16H33(CH3)CH-CH=CHOCH3 (+·)。
