A combined DFT-predictive and experimental exploration of the sensitivity towards nucleofuge variation in zwitterionic intermediates relating to mechanistic models for unimolecular chemical generation and trapping of free C2 and alternative bimolecular pathways involving no free C2. Issue 42 (24th October 2022)

• Record Type: Journal Article
• Authors: Rzepa, Henry S.; Arita, Miki; Miyamoto, Kazunori; Uchiyama, Masanobu
• Is Part Of: Physical chemistry chemical physics. Volume 24:Issue 42(2022)
• Page Start: 25816
• Page End: 25821
• Publication Date: 2022-10-24
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d2cp01214f
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Unimolecular fragmentation (path 1) of species 2 forming C2 is inferred from a gaseous trapping experiment whereas DFT calculations indicate an alternative bimolecular route (path 2), an experimental/theoretical dichotomy that remains unexplained. Abstract : Following the recent report of the chemical generation and trapping at room temperatures of C2, generated from an alkynyl phenyl iodonium salt, a computational analysis had indicated that both unimolecular fragmentation and bimolecular substitution mechanisms for the process could be envisaged. Here a combined theoretical and experimental analysis explores how the energetics of these mechanisms and resulting experimental products respond to variation in the nucleofuge. When the phenyl iodonium nucleofuge is replaced by pyridinium, trapping products are again obtained, which we conclude favours a bimolecular mechanism involving no free C2 . Trapped products in greater yield were also observed using dibenzothiophenium as the nucleofuge in both condensed solution phase and most significantly in a two-flask room temperature experiment in which a volatile species, presumed to be C2, is transferred and trapped in a second flask. The energetics of the unimolecular fragmentation process producing C2 are predicted to be too high to correspond to a facile thermal reaction, which means that an experimental/theoretical dichotomy remains to be explained.