Double-hydrogen rearrangement

A loss of 55 is possibly the loss of C4H7 from esters (double hydrogen rearrangement). The loss suggests a butyl or isobutyl group, especially when m/z 56 is also present. 

Benzoates (by double hydrogen rearrangement) (The ester must be ethyl or higher.)... 

The ion-trap multistage MS-MS mass spectra of protonated carbofuran (m/z 222) showed the loss of methyl isocyanate in the first stage to m/z 165, which in turn showed m/z 123 due to the loss of propylene, and a weak m/z 137, supposedly due to the loss of ethylene after double hydrogen rearrangement [25]. The m/z 123 could be further fragmented to protonated phenol dne to the loss of CO [25]. 

Postulate the product of the double-hydrogen rearrangement in octyl acetate. 

Similar to the mechanism shown in Eq. 6.36, mjz 61 [C(OH)2CH3]+ would be produced via the double-hydrogen rearrangement in ionized octyl acetate. 

As hydrogen rearrangements prior to dissociation are prevalent in alkenes, the radical site migrates along the chain, thereby obscuring the location of the double bond. [60]... 

McLafferty Rearrangement with Double Hydrogen Transfer... 

Alkene loss via McLafferty rearrangement at the alkoxy group of aliphatic and aromatic carboxylic acid esters competes with yet another reaction path, where two hydrogens instead of one as in the normal McLafferty product are transferred to the charge site. This second pathway leading to alkenyl loss has early been noticed [94] and became known as McLafferty rearrangement with double hydrogen transfer (r2H) ... 

Studying the competition of McLafferty rearrangement either with charge retention or charge migration and double hydrogen transfer has revealed that ion-neutral complex intermediates (Chap. 6.12) can also play a role for the latter two processes. [102]... 

Unimolecular dynamics of smaller clusters has also been studied. The HF dimer provides a particularly interesting system because it involves a highly quantal degenerate rearrangement consisting of a concerted double hydrogen-bond switch (Quack and Suhm 1991 Truhlar 1990). 

A C-11,12 double-bond rearranged product 24 was observed when 2, 7-deacetyl paclitaxel was treated with Yarovenko reagent (Et2NCF2CHFCl), which can be then transformed into 2 -Troc-10-deoxy paclitaxel (25) by catalytic hydrogenation, along with the formation of a small amount of 12-fluorinated 26. All taxoids, after deprotection, showed reduced cytotoxicity seven to eight times. 

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