Radicals 2-cyano-2-propyl

Heberger K and Fischer H 1993 Rate constants for the addition of the 2-cyano-2-propyl radical to alkenes in solution Int. J. Chem. Kin. 25 249-63... 

First examine the geometry of methyl radical. Is it planar or puckered Examine the geometries of 2-methy 1-2-propyl radical, trifluoromethyl radical, trichloromethyl radical and tricyanomethyl radical. Classify each of the substituents (methyl, fluoro, chloro and cyano) as a n-electron donor or as a Tt-electron acceptor (relative to hydrogen). Does replacement of the hydrogens by 7t-donor groups make the radical center more or less puckered Does replacement by Jt-acceptor groups make the radical center more or less puckered Justify your observations. 

The homolysis of AIBN occurs in a concerted process with simultaneous breakage of the two C— N bonds to yield nitrogen and 2-cyano-2-propyl radicals. Reaction of the radicals with each other can occur in two ways to yield tetramethylsuccinodinitrile and dimethyl-A-(2-cyano-2-isopropyl)ketenimine ... 

A minor reaction of 2-cyano-2-propyl radicals is disproportionation to methacrylonitrile and isobutyronitrile [Moad et al., 1984 Starnes et al., 1984]. This presents a complication for polymerizations carried out to high conversions where the methacrylonitrile concentration is significant since methacrylonitrile undergoes copolymerization with many monomers. 

It is characteristic that the new entrant methyl group assumes the ortho position to the nitro group and thus a substitution occurs which is similar to nucleophilic attack. Recently it has been found by Jackson and Waters [72] that higher nitrated benzene derivatives such as m- dinitrobenzene, or 1,3,5-trinitrobenzene, become homolytic hydrogen acceptors at temperatures of 80-100°C especially in the presence of the 2-cyano-2-propyl radical, which is formed by thermal decomposition of a,a -azo-bis-isobutyronitrile... 

In the presence of 2-cyano-2-propyl, using 0.72 mole of trinitrobenzene, acti-dine can be obtained in 64% yield, whereas without the radical the yield is only 4%. 

This reaction suggests that free radicals may act as reducing agents (Haines and Waters [73]). Indeed, Inamoto and Simamura [74] have recently proved that the 2-cyano-2-propyl radical can react with nitrobenzene to give small quantities of 0,N-di(2-cyano-2-propyl)-N-phenylhydroxylamine (I). 

A study of chemically induced dynamic electron polarization, CIDEP (see Section 12.3.3) on F and G pairs of radicals formed under photolysis of a common termo- and photoinitiator 2,2 -azobis(2-methylpropionitrile) (AIBN) led to a tentative conclusion that initial spatial separation of 2-cyano-2-propyl radicals does not depend upon viscosity However, it is plausible that the diamagnetic dinitrogen molecule formed under photolysis of AIBN (and is invisible by ESR) separates further from a contact RP under photolysis in solvents of lower viscosity. The problem of initial spatial separation and mutual orientation ofradicals under photolysis still waits experimental elucidation. 

In 1997, Paul s group also found an usual net emissive CIDEP spectrum of 2-cyano-2-propyl radicals when generated from 2,2 -azobis[isobutyronitrile] (AIBN) by triplet sensitization with thermally equilibrated triplet acetone ( S ) [12]. Here, this reaction occurs as follows ... 

Radicals and Aromatics. I. Reaction of Anthracene and of Pyrene with 2-Cyano-2-propyl Radicals. 

The 1,3,5-triphenylverdazyl coupling product with the 2-cyano-2-propyl radical was examined as a unimolecular initiator of the living free radical polymerization of styrene <1998PB539>. 

Obviously, the use of nitroxides as agents to control polymerizations remains interesting, however, their limitations makes one wonder whether there are other stable radicals which may be superior. Unfortunately, there are a limited number of stable radicals available, and those that have been studied have not been particularly successful. Earlier studies with galvi-noxyl radicals have been followed recently with the use of triazolinyl radicals and verdazyl radicals 1. However, in the only reported use of verdazyl radicals to mediate styrene polymerizations no control was observed with 2, an adduct of the 1,3,5-triphenylverdazyl radical and the 2-(2-cyano-2-propyl) radical derived from 2,2 -azobisisobutyronitrile (AIBN), at reaction temperatures between 80 °C and 120 In the case of the triazolinyl radicals, a spirotriazolinyl radical controlled the polymerization of styrene reasonably weU, but was only moderately effective for methyl methacrylate ... 

Homolytic Bond Scission. - 2.3.1 Azo compounds. Azo compounds such as 2,2 -azobisisobutyronitrile (AIBN) are widely used as polymerization in-itiators. Upon UV excitation AIBN decomposes into a nitrogen molecule and a geminate pair of two 2-cyano-2-propyl radicals ... 

Laser flash experiments of trans-azocumene using TR EPR have been reported by Savitsky et and a reversed TM CIDEP was observed with AIBN. These time-resolved investigations were extended by triplet sensitization of symmetrical azoalkanes with acetone and benzophenone. The photosensitized dissociation of AIBN yields a pair of 2-cyano-2-propyl radicals [2 R-] in a triplet or singlet state according to the reaction scheme... 

The radical-pair polarization (RPM) of the 2-cyano-2-propyl radical generated by laser flash photolysis of AIBN has been studied in solvents of various viscosities. The ratio of F-pair and geminate-pair polarization determined increases with higher viscosity. These results are discussed in terms of a viscosity-dependent cage effect. 

Scheme 24 Synthesis of 2-cyano-2-propyl dithiobenzoate by radical induced ester exchange. Reproduced from Moad, G. Rizzardo, E. Thang, S. H., Living Radical Polymerization by the RAFT Process. Aust J. Chem. 2005, 58, 379-410. ...

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