Bimolecular Homolytic Substitutions at Nitrogen: An Experimental and Theoretical Study on the Gas-Phase Reactions of Alkyl Radicals with NF3

Abstract

The X-ray irradiation of binary mixtures of alkyl iodides R-I (R=CH3 , C2 H5 , or i-C3 H7 radicals) and NF3 produces R-NF2 and R-F. Based on calculations performed at the CCSD(T), MRCI(SD+Q), G3B3, and G3 levels of theory, the former product arises from a bimolecular homolytic substitution reaction (SH 2) by the alkyl radicals R, which attack the N atom of NF3 . This mechanism is consistent with the suppression of R-NF2 by addition of O2 (an efficient alkyl radical scavenger) to the reaction mixture. The R-F product arises from the attack of R to the F atom of NF3 , but additional contributing channels are conceivably involved. The F-atom abstraction is, indeed, considerably more exothermic than the SH 2 reaction, but the involved energy barriers are comparable, and the two processes are comparably fast.

Keywords: X-ray radiolysis; alkyl radicals; bimolecular reactions; density functional calculations; nitrogen trifluoride; substitution reactions.