Generation of neutral CCCCBO in the gas phase from [CCCCBO]⁻ and rearrangement of energized CCCCBO to OCCCCB: A joint experimental and theoretical investigation

Abstract

One-electron vertical Franck - Condon oxidation of [CCCCBO]- (using O2 as collision gas in the dual collision cell region of an HF-ZAB/AMD 604 four-sector mass spectrometer) forms doublet neutrals C 4BO in the first stage of a neutralization - reionization ( -NR+) experiment. Reionization of these neutrals to decomposing positive ions shows that the majority of neutrals (formed in the first collision cell) correspond to CCCCBO which are stable for the microsecond duration of the NR experiment. However, a minor fraction of neutrals CCCCBO is energized and rearranges to form an isomer which decomposes by loss of CO. A theoretical study of this system at the MP4SDTQ/aug-cc-pVDZ//MP2(full)/6-31G(d) level of theory suggests that the rearranged species corresponds to OCCCCB. The rearrangement occurs by six-center cyclization of CCCCBO, involving O - C(1) bond formation followed by B - O bond cleavage to form OCCCCB. The reaction is endothermic by only 4.5 kcal mol-1 but requires an excess energy of ≥ 53.5 kcal mol-1 in order for the system to surmount the first transition state. This energy requirement is 45.5 kcal mol-1 more than the Franck Condon excess energy of 8 kcal mol-1 of CCCCBO produced by the vertical oxidation process. The additional energy may be provided by keV collisions of CCCCBO with the collision gas O2 following Franck-Condon-controlled neutralization of [CCCCBO]-.