II. Thermal nitration of olefins with tetranitromethane. Evidence for homolytic initiation of a chain mechanism

Abstract

AbstractTetranitromethane (TNM) reacts spontaneously with N‐vinylcarbazole to afford the product of 1,2‐addition. Under the same conditions, 9‐vinylanthracene and other olefins do not react with TNM until they are deliberately stimulated by a short pulse of visible light. Photo‐activation under these conditions is associated with the charge‐transfer excitation of the olefin‐TNM complex to produce NO2. The subsequent homolytic addition of NO2 to the olefinic donor, followed by electron transfer of the radical adduct, is responsible for the novel chain mechanism for TNM addition in Scheme 1. Homolytic initiation can also be achieved chemically with various additives such as the electron‐rich ferrocene, N,N,N′,N′‐tetramethyl‐1,4‐phenylenediamine, and 5H‐dibenz[b,f]azepine which generate NO2 by dissociative electron attachment to TNM. The limited quanta of light and traces of chemical initiators indicate that the chain mechanism for the addition of TNM occurs with relatively long kinetic chain lengths. The mechanistic implications of the chain mechanism for the formation of various types of products is discussed in the context of olefin structures.