Hydrogen abstraction, ketones proton transfer

Competing reactions may introduce mechanistic ambiguities Ketone or quinone triplet states abstract hydrogen atoms, forming neutral radicals. Also, many radical cations are proton donors and radical anions are comparably strong bases. Thus, geminate radical ion pairs may generate neutral radicals by proton transfer. 

As in hydrogen transfer between alcohols and saturated ketones, the rate-determining step in the reaction with a,p-unsaturated ketones is hydrogen abstraction from the a-carbon atom. It has been suggested that the hydrogen atom is transferred directly to the P-carbon of the enone, yielding an in -oxaallyl complex which following protonation yields the saturated ketone. ... 

Computer simulation of intramolecular hydrogen atom transfer to carbonyl oxygen has been achieved by a Monte Carlo method. In particular, the model has been found to give good agreement when applied to intramolecular P-, y-, 6-, -, and ( -hydrogen atom abstraction in ketones as well as q- and 0-proton transfer in oxoesters, and it has also been used to predict the reactivities of... 

Cationic photoinitiators are usually based on iodonium salts [e.g. Phal ) and sulfonium salts (e.g. PhsS" ") which liberate a proton upon exposure to UV light (after subsequent rearrangement of the primary pairs formed, cleavage of a C-I or C-S bond and/or hydrogen abstraction on a H-donating structure). Photoinitiators of radical polymerization were originally classified as Type I PI (cleavable systems e.g. aryl allq l ketones or phosphine oxides mostly through a Norrish I scission, Scheme 2a) and Type II PI (PI and a co-initiator such as an amine AH or electron/proton transfer process, Scheme 2b PI stands e.g. for benzophenones. 

Proton Abstraction Proton transfer in NCI can be understood as proton abstraction from the sample molecule. In this way, all substances with acidic hydrogens, for example, alcohols, phenols or ketones, can undergo soft ionization. 

A great variety of substituted enolates can be obtained by the addition of nucleophiles (XeMe) to enones (for X = trialkylsilyl, see Section D.4.3.). Reductive formation of these enolates (where X = hydrogen), however, can be achieved either by hydride transfer or by a two-electron reduction combined with proton abstraction from a suitable partner. Consecutive protonation produces the diastereomeric ketones. 

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