Substituent Effects on the Rearrangement of Phenylnitrene

Abramovitch and Banks discovered that polyfluorinated phenylnitrene participates in intermolecnlar chemistry. Interestingly, perflnoro- and 

6-difluorophenylnitrene react with pyridine but 4-fluorophenylnitrene undergoes 

Sundberg has observed products of the rearrangement of 2-alkylsubstituted phenylnitrenes that indicated that the initial cyclization is toward the unsubstituted ortho carbon (the presumed intermediate 20 in Reaction 5.4). Matrix isolation studies of 2,4-dimethylphenylnitrene find very little rearrangement product.  

CASPT2 error in computing the barrier for 1 is the same as for 21b and 21c, then the agreement with experiment is quite good. 

On the other hand, fluorine substitution at both ortho positions (21a) raises the CASPT2/6-31G barrier from 8.6 to 13.0 kcal mol The increase in the barrier height inhibits the rearrangement reaction and allows 21a to participate in intermolecular chemistry. Subsequent experiments determined that its activation barrier is 7.3-8.0 kcal mol (depending on the solvent). Calculations predict a 

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