Collision-induced dissociations of aryl-substituted alkoxide ions. Losses of dihydrogen and rearrangement processes

Abstract

The ion PhCH₂O^– undergoes competitive losses of H˙, H₂, CH₂O, and C₆H₆ upon collisional activation. The loss of H₂ occurs mainly to form (C₆H₄)^–CHO, and ab initio calculations suggest the reaction proceeds by the stepwise mechanism PhCH₂O^–→[H^–(PhCHO)]→(C₆H₄)^–CHO + H₂. The losses of CH₂O and C₆H₆ are accompanied (or preceded) by partial phenyl H–benzyl H interchange. The ion Ph(CH₂)₃O^– undergoes many fragmentations including the losses of H₂O and, CH₂O and loss of H₂. The loss of H₂ occurs by both 1,2- and 1,3-eliminations. A number of minor fragmentations occur after partial interchange of phenyl hydrogens and hydrogens at position 2. The first example of a specific double proton transfer is noted, viz. Ph(CH₂)₃O^–→ C₆H₇^–+ CH₂CH–CHO. Ions Ph(CH₂)_nO^–(n= 2–5) all decompose to produce PhCH₂^– ions: when n= 3–5 it is proposed that the reactions may involve Smiles intermediates, i.e. reaction (a). [graphic omitted]