The formation of CCBO and [CCBO]⁺ from [CCBO]⁻ in the gas phase: A joint experimental and theoretical study

Abstract

The stable anion [CCBO]- may be formed in the chemical ionization source of a mass spectrometer by the process F- + (CH3)3Si-CC-B(O-iso-Pr)2 [CCBO]- + (CH3)3SiF + CH3-CH=CH2. Anion [CCBO]- may be converted to stable doublet CCBO by a collision-induced vertical Franck-Condon oxidation in the first of two collision cells. Calculations at the MP4SDTQ/aug-cc-pVTZ//MP2(full)/6-31G(d) level of theory indicate that [CCBO]- and CCBO are linear species, with structures approximated by valence bond forms [:C=C=B=O]- and ·CC-B=O, respectively. Neutral CCBO may be converted to [CCBO]+ in the second collision cell by vertical ionization. Some of the [CCBO]+ cations are stable, while others are energized and undergo rearrangement to [OCCB]+. This exothermic rearrangement may occur for both the singlet and triplet forms of [CCBO]+ (the triplet form is lower in energy by only 5.2 kcal mol-1) with both rearrangements proceeding through distorted rhombic forms of [cyclo-CCBO]+.