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Analytical Chemistry
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Common Fragments; Characteristic Peaks Cleavage of all C-O, C-H, and C-C bonds around the original aldehydic carbon Loss of 18 (H2O -- usually by cyclic mechanism); loss of H2O and olefin simultaneously with four (or more) carbon-chain alcohols; prominent peak at m/z = 31(CH2ÖH)+ for 1° alcohols; prominent peak at m/z = (RCHÖH)+ for 2° alcohols; and m/z = (R2CÖH)+ for 3° alcohols Loss of aldehydic hydrogen (strong M-1 peak, especially with aromatic aldehydes); strong peak at m/z = 29(HCO+); loss of chain attached to alpha carbon (beta cleavage); McLafferty rearrangement via beta cleavage if gamma hydrogen is present Loss of 14 mass units (CH2) Cleavage at the point of branch; low intensity ions from random rearrangements Loss of 28 mass units (CH2=CH2) and side chains Loss of units of general formula CnH2n-1; formation of fragments of the composition CnH2n (via McLafferty rearrangement); retro Diels-Alder fragmentation
GC/MS and DFT studies of S,S-dialkyl methylphosphonothioloselenoates related to Schedule 2.B.04 of Chemical Weapons Convention
Published in Journal of Sulfur Chemistry, 2019
Hamid Saeidian, Ali Soleimani Karimabad, Mahmood Payeghadr, Mehran Babri
Expulsion of an alkyl group on the sulfur of M+• as a neutral alkene, via McLafferty-type rearrangement, led to the formation of fragment ion [A] in all EI-MS of chemicals 3 and 4. The McLafferty-type rearrangement was more prominent for large and branched alkyl substituents, especially where one of the alkyl groups was an ethyl group (Table 3). Stability of the eliminated alkene is important for McLafferty-rearrangement. According to Saytzeff’s rule, highly substituted alkenes are more stable. Fragment ion [B] was formed through loss of thioaldehyde/thioketone from M+•. It is worthy to note that elimination of sec-alkyl as thioketone from M+• is easier than n-alkyl as thioaldehyde (Tables 2 and 3). Formation of ion [B] can be explained by two mechanisms based on hydrogen migration involving selenium and phosphorus atoms which led to two possible structures (Scheme 5). The free energy of the [CH3-PSe(SPr)H]+•, as calculated by Gaussian 03 in the case of R = R′ = propyl, was found to be 37 kJ mol−1 lower than that of the [CH3-P(SPr)SeH]+•, indicating 1,4 C-Se hydrogen migration as the preferred mechanism rather than the 1,3 C–P H shift.