Polar reaction mechanisms

Using Curved Arrows in Polar Reaction Mechanisms 149... 

Rules for using curved arrows in polar reaction mechanisms (Section 5.6). 

Using Curved Arrows In Polar Reaction Mechanisms... 

The Diels-Alder reaction cannot be explained adequately by the familiar polar reaction mechanism involving electron pair interactions or by a free radical mechanism. In fact in older literature, it was sometimes described as a no-mechanism reaction. There are no intermediates, and kinetic studies show that the reaction is first order in both the diene... 

Curly arrows can be used to represent bond cleavage. A double-headed arrow represents the movement of two electrons (and is used in polar reaction mechanisms). A single-headed arrow (or fish-hook) is used to represent the movement of... 

USING CURVED ARROWS IN POLAR REACTION MECHANISMS... 

Upon oxidation, the subsequent radical cation can decompose in a number of different ways to generate reactive intermediates (Scheme 10.1). The first possibility involves direct H-atom abstraction of the a-C-H bond of the oxidized amine (I) to generate an iminium ion (II), which is susceptible to nucleophilic attack via polar reaction mechanisms (pathway a). Deprotonation of I may also form a carbon-centered radical species (III) that can react with typical radical traps, such as olefins or arenes (pathway b). Generation of the iminium ion may also occur indirectly through oxidation of III via SET to the photocatalyst or another oxidant (pathway c). Finally, radical cation I can undergo non-productive pathways such as back-electron transfer with the reduced photocatalyst (PC" ) to re-generate the neutral amine and PC" (pathway d). 

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